Self-assembly of highly charged polyelectrolyte complexes with superior proton conductivity and meth

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Activity and lifetime of urease immobilized using layer-by-layer nano self-assembly

Nanoscale Self-Assembly of Urease in a Si Microreactor 85Applied Biochemistry and Biotechnology Vol. 121–124, 2005Copyright © 2005 by Humana Press Inc.All rights of any nature whatsoever reserved.0273-2289/05/121–124/85–92/$30.0085*Author to whom all correspondence and reprint requests should be addressed.Activity and Lifetime of UreaseImmobilized Using Layer-by-Layer NanoSelf-Assembly on Silicon MicrochannelsS COTT R. F ORREST , B ILL B. E LMORE , AND J AMES D. P ALMER *Louisiana Tech University, Chemical Engineering Program,600 W. Arizona, P.O. Box 10348 TS, Ruston, LA 71272,E-mail: jpalmer@AbstractUrease has been immobilized and layered onto the walls of manufactured silicon microchannels. Enzyme immobilization was performed using layer-by-layer nano self-assembly. Alternating layers of oppositely charged poly-electrolytes, with enzyme layers “encased” between them, were deposited onto the walls of the silicon microchannels. The polycations used were polyethylenimine (PEI), polydiallyldimethylammonium (PDDA), and polyallylamine (PAH). The polyanions used were polystyrenesulfonate (PSS)and polyvinylsulfate (PVS). The activity of the immobilized enzyme was tested by pumping a 1 g/L urea solution through the microchannels at various flow rates. Effluent concentration was measured using an ultraviolet/visible spectrometer by monitoring the absorbance of a pH sensitive dye. The architecture of PEI/PSS/PEI/urease/PEI with single and multiple layers of enzyme demonstrated superior performance over the PDDA and PAH architectures. The precursor layer of PEI/PSS demonstrably improved the performance of the reactor. Conversion rates of 70% were achieved at a residence time of 26 s, on d 1 of operation, and >50% at 51 s, on d 15 with a six-layer PEI/urease architecture.Index Entries: Silicon microchannels; urease; architecture; polyelectro-lytes; first-order constant.IntroductionChemical microsystems provide a combination of advantages—highly defined flow, reduced diffusion distances, and small size and catalyst requirement—for a variety of applications in sensors, process develop-ment, and chemical synthesis. Silicon-based microreactors have the benefitof the mature and refined processes that allow microchannel dimensions of86Forrest et al.5 µm or less. Immobilization of enzymes on the surface of silicon (1) and silicon microchannels (2–4) has been demonstrated in the literature using covalent attachment with various silane linkers. In this work, immobiliza-tion of enzymes on silicon walls is performed using layer-by-layer self-assembly.Layer-by-layer self-assembly is a technique in which thin films are created by sequentially applying oppositely charged polyelectrolytes to a surface (5). In the 1990s, Decher (6) proposed this technique and has recently coauthored a book on this subject (7). In 2000, more than 200articles on polyelectrolyte multilayers were published (8). A screening study demonstrating the deposition of urease on a gold-coated quartz crystal resonator has recently been reported in the literature (9). Poly-styrenesulfonate (PSS) and polydiallyldimethylammonium (PDDA) were the polyelectrolytes employed in that study. The present study extends the prior work by applying the multilayers in silicon microchannels, and comparing the efficacy of various architectures through the measurement of first-order rate constants and deactivation rates.Materials and MethodsSilicon microchannels were produced in a clean-room facility at Loui-siana Tech. Photolithography was used to transfer the pattern from a chrome mask to a positive photoresist coated on a <1,0,0> silicon wafer. The channels and vias were etched using an Actel A601 Inductive Coupling Plasma (ICP) employing the Bosch process. The ICP allows high-aspect-ratio vertical sidewalls vs competing technologies such as wet etching. The microreactors consist of an inlet and a manifold, which feed 98 parallel microchannels, each 2.7 cm in length. Each channel is 60 µm wide and 100 µm deep. The channels then feed into a manifold and outlet. Figure 1is an image from an Amray 1830 Scanning Electron Microscope (SEM)showing the inlet region and microchannels of a microreactor.Fig. 1. Scanning electron microscope photograph of inlet and manifold of siliconmicroreactor.Nanoscale Self-Assembly of Urease in a Si Microreactor 87Urease Canavalia ensiformis with a specific activity of 54,300 U/g was obtained from Sigma (St. Louis, MO). The urea, trizma hydrochloride (Tris-H Cl), tris(hydroxy methyl)aminomethane (Tris base), and thymol blue were all ACS reagent-grade products obtained from Sigma-Aldrich. The polycations utilized were polyethylenimine (PEI), polyallylamine (PAH),and PDDA with mol wts of 25,000, 15,000, and 150,000, respectively. The polyanions utilized were PSS and polyvinylsulfate (PVS) with mol wts of 70,000 and 170,000, respectively. Type 1 reagent-grade water was obtained using a Barnstead Series 1090 E-Pure reverse osmosis purifier and utilized for all experiments.The aqueous feed solution to the microreactor contained 16.7 m M urea,7.6 m M Tris-HCl, 8.3 m M Tris base, and 42.9 m M thymol blue. Thymol blue was chosen owing to its operation in a region optimal for the activity of the urease. The Tris-HCl and Tris base concentrations were chosen to provide sensitivity of the pH indicator over all ranges of urease conversions. A standard curve of the thymol blue indicator was determined using known aliquots of ammonium hydroxide. The end point of 100% conversion was confirmed by testing the absorbance of the feed solution with the free enzyme. The absorbance at 600 nm was measured using an Ocean Optics SD-2000 ultrviolet/visible spectrometer and an AIS mini-DTA deuterium tungsten halogen light source. An extinction coefficient of 27.7 for the pro-duction of NH 3 as indicated by thymol blue was determined for this system.Polyelectrolyte solutions were prepared in aqueous solutions at pH8.5 and concentrations of 2 g/L for PSS, PEI, and PDDA solutions and 1 g/L for PVS and PAH solutions. Layering was performed by immersing the microreactor into the appropriate polyelectrolyte solution for a period of 10min followed by a 1-min rinse of Tris buffer. Urease deposition was per-formed by immersing the microreactor in a 1 g/L solution for 20 min fol-lowed by a 1-min Tris buffer wash.An experimental setup, depicted in Fig. 2, was constructed that allowed three reactors to be operated simultaneously. A syringe pump with threeFig. 2. Experimental setup with multiple reactors.88Forrest et al.syringes and feed lines pumped the feed solution into each individual reac-tor. Samples were collected and analyzed off-line using the Ocean Optics SD-2000 UV/V spectrometer. Different layer-by-layer architectures were applied to each of the reactors to compare the resultant catalytic activity. The experiments were continued over a period of days to assess the decay in activity.Results and DiscussionTable 1 depicts the architectures tested in our study. As already stated,the enzyme activity of all architectures was characterized by measuring the conversion of urea as a function of microreactor residence time. Figure 3depicts the activity observed by architecture 7, with each curve represent-ing the activity on a particular day. Figure 4 depicts the first-order rate constant regression using the integral method over the various days of operation. The regressed first-order rate constants were the basis of com-parison among enzyme architectures.Table 1Polyelectrolyte Architectures Tested aNumberArchitecture Day 1 rate constant (s –1)1PDDA/PSS/PDDA/urease/PDDA 0.00422PDDA/PSS/PDDA/(urease/PDDA)4 a 0.00713PAH/PVS/PAH/urease/PAH 0.00404PEI/PVS/PEI/urease/PEI 0.00535PEI/urease/PEI 0.02106PEI/PSS/PEI/urease/PEI 0.03217PEI/PSS/PEI/(urease/PEI)6 a 0.1588aMultiple layers of enzyme and polyelectrolytes.Fig. 3. Conversion rate for PEI/PSS/PEI/(urease/PEI)6.Nanoscale Self-Assembly of Urease in a Si Microreactor89Fig. 4. Rate constant curves for PEI/PSS/PEI/(urease/PEI)6.Architectures 1 and 2 were based on PDDA as the polycation and PSS as the polyanion. The activity observed for these architectures was very low, even with multiple layers of enzymes, and was abandoned for this reason.The PEI/PSS polyelectrolytes of architecture 5 were superior to the PAH/PVS and PEI/PVS polyelectrolytes of architectures 3 and 4, respec-tively, in terms of first-order rate activity. First-order rate activity for d 1 of the PEI/PSS architecture was more than four 4 times greater than that of the PEI/PVS architecture and more than five times greater than that of PAH/ PVS architecture (Table 1). Even on d 20 of operation, the first-order rate activity of the PEI/PSS reactor was higher than for the other two architec-tures on the first day of operation. The PEI/PSS reactor produced conver-sions of about 60% at 102 s of residence time on d 1, compared with 17 and 24% for the PAH/PVS and PEI/PVS reactors, respectively. By d 20, the PEI/PSS reactor produced a peak conversion of 18% at the highest resi-dence time tested. Peak conversion rates for the PAH/PVS and PEI/PVS reactors had dropped to 5 and 10%, respectively. For this reason, further efforts concentrated on PEI/PSS-based architectures.An experiment was performed making a PEI/urease architecture without the PEI/PSS precursor layer (architecture 5). The PEI/PSS precur-sor layer (architecture 6) was found to have a 50% higher d 1 first-order rate constant. A 26-s residence time resulted in 50% conversion with the precur-sor layer and only 25% conversion without the precursor layer.An enzyme architecture with the PEI/PSS precursor layer and six multiple layers of PEI/urease was compared with a similar architecturecontaining only one enzyme layer. As expected, the increase in enzymelayers dramatically increased the activity of the reactor. The six layers of enzyme had a first-order rate constant five times higher than the single-90Forrest et al.layer experiment (Table 1). The conversion of the single-layer and six-layer enzyme architecture was 50and 70%, respectively, on d 1 for a residence time of 26 s. Figure 5 depicts the decay rate of the first-order rate constants for the three PEI/urease architectures tested. The six-layer architecture exhibited an exponential decay in activity. The single-layer architectures had much lower initial activities but retained this activity at a relatively constant rate, especially after the initial decay observed in the first 5 d of operation. Reactor product samples once obtained were monitored succes-sively over time (i.e., a period of days) and no further reaction was noted.This evidence suggests that the decay in activity was not owing to losses of the enzyme into the product effluent but, rather, to denaturing of the enzyme. Protein assays of the reactor and effluent are under way and will be reported at a later date.ConclusionLayer-by-layer nano self-assembly is a convenient and inexpensive technique for immobilizing enzymes on the surface of silicon microreac-tors. Extremely high surface area to volume available in a microreactor provides a maximum opportunity for reactions at the channel walls. Of the architectures tested, PEI is the best choice for immobilizing urease. A pre-cursor layer of PEI/PSS was found to increase significantly the activity of the subsequent enzyme layers. Microreactors with layer-by-layer encased enzymes showed significant activity after more than 2 wk. The conversion rate for the best microreactor in our study exhibited 70% conversion on d 1 of testing and was still converting >50% of urea solution at residence times under 1 min after 15 d. Experiments using microreactors with chan-nel widths of 5 µm are ongoing. The reduced diffusion distances shouldFig. 5. Comparison of first-order rate decay.Nanoscale Self-Assembly of Urease in a Si Microreactor91 further demonstrate the advantage of the microreactor compared with other reactors with similar surface areas.AcknowledgmentThe authors wish to thank Dr. Yuri Lvov at Louisiana Tech’s Institute for Micromanufacturing for assistance in applying layer-by-layer self-assembly techniques.References1.Subramanian, A., Kennel, S. J., Oden, P. I., Oden, K. B., Jacobson, K. B., Woodward,J., and Doktyez, M. J. (1999), Enzyme Microb. Technol.24, 26–34.2.Pijanowska, D., Remiszewska, E., Lysko, J., Jazwinski, J., and Torbiez, W. (2003),Sensor Actuat. B91, 152–157.3.Yakovleva, J., Davidsson, R., Lobanova, A., Bengtsson, M., Eremin, S., Laurrell, T.,and Emneus, J. (2002), Anal. Chem.74, 2994–3004.4.Bengtsson, M., Ekstrom, S., Marko-Varga, G., and Laurell, T. (2002), Talanta56, 341–353.5.Lvov, Y. and Mohwald, H. (2000), Protein Architecture: Interfacing Molecular Assemblyand Immobolization Biotechnology, Marcel Dekker, New York, NY.6.Decher, G. (1997), Science227, 1232–1237.7.Decher, G. and Schlenoff, J. (2003), Multilayer Thin Films—Sequential Assembly ofNanocomposite Materials, Wiley-VCH , Weinheim, Germany.8.Freemantle, M. (2002), Chem. Eng. News80(8), 44–48.9.Disawal, S., Qiu, J., Elmore, B., and Lvov, Y. (2003), Colloids Surf. B Biointerfaces32,145–156.。

DPBF单重态氧

Dye -Polyelectrolyte Layer-by-Layer Self-Assembled Materials:MolecularAggregation,Structural Stability,and Singlet Oxygen PhotogenerationMartı´n Mirenda,†Cristian A.Strassert,‡Lelia E.Dicelio,†and Enrique San Roma ´n*,†INQUIMAE/DQIAyQF,Facultad de Ciencias Exactas y Naturales,University of Buenos Aires,Ciudad Universitaria,Pab.II,C1428EHA,Argentina,and CeNTech,Physikalisches Institut Westfa ¨lische Wilhelms-Universita ¨t Mu ¨nster,Heisenbergstrasse 11,D-48149,GermanyABSTRACT The interaction of rose Bengal (RB)and ﬂuorescein (FL)with poly[diallyldimethylammonium]chloride (PDDA)was studied in layer-by-layer self-assembled thin ﬁlms and in solution.The spectroscopic behavior is explained in terms of dye -dye,dye -polyelectrolyte,and in solution,dye -solvent interactions.A correlation among dye hydrophobicity,aggregation tendency,polymer folding in solution,and the stability of self-assembled ﬁlms is obtained.In spite of the very high dye concentration (∼1M),RB-PDDA multilayer thin ﬁlms are able to photogenerate singlet molecular oxygen,as demonstrated by chemical monitoring and IR phosphorescence detection.KEYWORDS:layer-by-layer self-assembly •rose bengal •ﬂuorescein •ﬂuorescence •singlet molecular oxygenINTRODUCTIONThe inclusion of organic dyes into polymeric ﬁlms and other structured media is of great interest in the development of new materials with potential applica-tions in many areas of technology as diverse as light harvest-ing (1),singlet molecular oxygen (1O 2)photosensitization (2),and even heterogeneous photocatalysis (3).In particular,immobilized singlet oxygen photosensitizers are found to be highly sought-after materials for practical applications,such as water decontamination,chemical reactions,and ﬁne-chemical synthesis,because of their convenient removal from the reaction medium (4).One of the main obstacles in the development of this class of materials is the formation of molecular aggregates or statistical energy traps at the required high local concentrations,particularly if dye mol-ecules are distributed at random (5).Nonradiative deactiva-tion pathways are favored in this case,with the concomitant lowering of relevant photoprocess quantum yields.A long time ago,Neckers and others showed that the 1O 2photoge-neration quantum yield,Φ∆,diminishes with concentration in polystyrene-based materials,when the dye molecules are randomly distributed (6).In coincidence with these observa-tions,San Roma ´n and co-workers reported recently that ﬂuorescence self-quenching of Rhodamine 6G randomly adsorbed on microcrystalline cellulose sets in at loadings as low as 0.005molecules/nm 2,with up to 50%quenching atsurface concentrations in the order of 0.05molecules/nm 2(7).It is clear that to limit statistical energy trapping,we need architectures with a high degree of structural control at the molecular level.An interesting strategy for the design of thin ﬁlms with high dye concentrations and restricted molecule proximity is the layer-by-layer,supramolecular electrostatic self-as-sembly.This technique was employed originally for the alternating adsorption of colloidal particles on solid sub-strates (8)and extended more than 20years later to the assembly of oppositely charged polyelectrolytes (9)and diverse soluble polyions such as nucleic acids (10)or en-zymes (11)and small molecules,including dyes (12-14).A rather limited number of authors have so far related the spectroscopic properties of dyes with their degree of ag-gregation within ﬁlms (15,16),and in general,no reference is made to the inﬂuence of interactions among dye mol-ecules on the stability and photoactivity of this kind of self-assembled materials.The quantitative investigation of dye aggregation is not straightforward in this case and cannot be carried out directly because the concentration of the dye,which is actually a structural part of the ﬁlm,cannot be varied at will as it will be discussed later.Therefore,it is necessary to make use of indirect methods.In this context,we have recently shown that the photophysical analysis of the interaction of dye and polyelectrolyte in solution pro-vides helpful information for the physicochemical charac-terization of self-assembled thin ﬁlms (17).We report now a comparative photophysical and photo-chemical investigation of layer-by-layer self-assembled ar-rays of poly[diallyldimethylammonium]chloride (PDDA)with two model xanthene dyes,rose Bengal (RB)and*Corresponding author.E-mail:esr@qi.fcen.uba.ar.Received for review March 8,2010and accepted May 19,2010†University of Buenos Aires.‡Physikalisches Institut Westfa ¨lische Wilhelms-Universita ¨t Mu ¨nster.DOI:10.1021/am100195v 2010American Chemical Society1556VOL.2•NO.6•1556–1560•2010Published on Web 05/24/2010ﬂuorescein(FL),as balancing counterions.The substitution pattern of the xanthene ring determines the contrasting behavior of both dyes in regard to their photophysics and aggregation tendency.On one hand,the highly hydrophilic FL evidences in solution a pH dependentﬂuorescence quantum yield,ΦF,near unity in alkaline solutions(18). Quite oppositely,the rather hydrophobic RB displays a low ΦF and a high triplet state quantum yield,ΦT,as well as a largeΦ∆(19).The main goal of this work is to correlate the stability and photophysical properties of the self-assembled thinﬁlms with the hydrophobicity and the aggregation tendency of the dyes.It is shown that solution experiments provide a rationale for the analysis of speciation of self-assembled materials.The photogeneration of1O2from RB thinﬁlms is reported and discussed in terms of theﬁlm structure.Self-Assembled Arrays of RB and PDDA.The layer-by-layer self-assembly ofﬁlms on glass substrates employing RB and PDDA has been recently reported.Such arrays constitute a novel class of nanostructured materials due to their singular architectures and photophysical proper-ties(17).The spectroscopic analysis revealed high local dye concentrations(∼1M)with a polyelectrolyte/dye ratio P/D ≈7,expressed in terms of dye and polyelectrolyte mono-meric units.The aggregation degree is only55%,an unusu-ally low value for such a high chromophore density com-pared with the same system in solution(see Experiments in Solution below).The availability of monomeric RB sug-gests that irradiation of theseﬁlms might lead to triplet state formation and,in the presence of dioxygen,to the photo-generation of1O2.Two independent techniques were used in order to verify this hypothesis:the bleaching of a chemical monitor that reacts with photoproduced1O2,and the sta-tionary detection of1O2phosphorescence at1270nm.Preliminary attempts to monitor1O2in water using N,N-dimethyl-p-nitrosoaniline and imidazole produced very fast desorption of RB.Therefore,1,3-diphenylisobenzofuran (DPBF)in dichloromethane solution was used as the chemi-cal monitor.The absorbance of the chemical monitor(λmax )415nm)decreases noticeably when the assembledﬁlm is immersed in the solution and irradiated at the RB absorp-tion band due to the peroxidation of DPBF by the photoge-nerated1O2.No decrease in the monitor absorbance is detected in the dark or under irradiation in the absence of theﬁlm.We quantitatively tested the photosensitization quantum yield of arrays consisting of12bilayers of RB/PDDA at each side of the glass substrate,using a methylene blue solution (MB)as a reference(Φ∆R)0.57in dichloromethane)(20). The time-dependent absorbance decrease of DPBF,obtained by irradiation of RB assemblies and MB in solution,is shown in Figure1a.Assuming that the product of the quenching rate constant of1O2by the concentration of DPBF is signiﬁ-cantly higher than the decay rate constant(see the Support-ing Information),it is possible to calculateΦ∆according to the following equation(21)where I A stands for the absorbed photonicﬂux(µEinstein dm-3s-1)and r for the reaction rate(µM s-1);superscript R identiﬁes the reference.Results lead toΦ∆)0.020(0.005. This value is much lower than the reported ones for the monomeric dye in various solvents(22),but remarkably large when taking into account the very high local concen-tration of the dye within theﬁlm.As the bilayer height can be estimated as1nm(17),photogenerated1O2will be able to diffuse freely and react with adsorbed substrates without substantial loss within the support.The photogeneration of1O2was further veriﬁed by steady state infrared emission spectroscopy.Figure1b depicts the stationary phosphorescence spectrum of a self-assembled array with9bilayers,measured in air upon excitation at45°. The emission band centered at1270nm can be unambigu-ously assigned to the phosphorescence of1O2(the growth of the baseline at the shorter wavelengths is mainly origi-nated by light scattering).Phosphorescence is not detected if the array is previously immersed into a DPBF solution and dried,pointing to monitor adsorption.However,adsorption takes place at the trace level because it remains undetectable by absorption spectroscopy(see the Supporting Informa-tion).FIGURE1.(a)DPBF absorbance decrease with increasing irradiation times employing self-assembled arrays with RB(triangles)and MB in solution(circles).(b)Steady-state phosphorescence spectrum of a self-assembled RB-PDDA array in air(λex)575nm).Φ∆)Φ∆RI A R rI A r R(1)LETTER VOL.2•NO.6•1556–1560•20101557Self-Assembled Arrays of FL and PDDA.Figure2a depicts the normalized absorption spectra of self-as-sembled arrays with 3,6,9,and 12bilayers of FL/PDDA at each side of the glass substrate.All spectra display the same shape,showing a maximum at 526nm,36nm red-shifted with respect to aqueous alkaline solutions.Spectra in water and in the ﬁlms can be decomposed as a linear combination of three Gaussians (see Figure 2b,c):each Gaussian belong-ing to the ﬁlm can be obtained from the corresponding one in water,37nm red-shifted and 35%widened.This analysis suggests the sole presence of the dianionic,monomeric dyewithin the ﬁlm.Furthermore,a markedly different ratio of bands would be observed if aggregated forms were present (23,24).The red shift can be attributed to the increase of polarity originated by the polycationic nature of the poly-meric matrix (13)and the spectral widening to heterogene-ities of the microenvironment within the assembly.These results allowed us to estimate the volumetric concentration of FL molecules in the self-assembled ﬁlms,assuming that the oscillator strength within the bilayers is similar to the one reported for the monomer in solution.Considering a molar absorption coefﬁcient of 74000M -1cm -1)7.4×107mol -1cm 2(18),and a bilayer absorbance of 0.0017at the maximum (Figure 2a),it is possible to estimate a numeric density in the order of 0.0017×6.02×1023/7.4×107cm -2)0.14molecules/nm 2.Considering a density of 3.7positive charges nm -2within the polyelectro-lyte bilayer (17),it can be deduced that FL is incorporated at a ratio of one molecule every 27PDDA monomeric units (P/D ≈27).Remaining polyelectrolyte charges are compen-sated by Cl -or OH -ions during assembly.Adding a new polyelectrolyte layer,dye molecules originally bound to the last one bind to the newly formed layer,shifting one coun-terion.Currently,the spectroscopic properties of the as-semblies depend on the nature of the last layer,either dye or polyelectrolyte,because the dye arrangement is quite different in both situations (16).Assuming a bilayer thickness of 0.53nm (16),a volumetric concentration of the dye in the order of 0.4M is obtained.The dianionic dye is the predominant species within the bilayers,without any spec-troscopically relevant degree of aggregation,despite its high local concentration.A signiﬁcant desorption of FL is observed in aqueous solution.Films formed with RB are comparatively more stable and allow the accumulation of subsequent bilayers without substantial loss of dye.Attempts to change the dye concentration in the ﬁlms by varying the composition of the dipping solutions were unsuccessful.More concentrated solutions do not yield higher incorporation.This is under-standable in RB ﬁlms because the polyelectrolyte is nearly saturated with dye molecules.Even though the P /D ratio is much higher in the FL ﬁlms,loading remains essentially unaffected on increasing the dye concentration.In the latterFIGURE 3.Speciation diagram of RB in PDDA solution as a function of the P/D ratio:monomer in solution (RB S 2-,circles),aggregates (RB n ,triangles),and polyelectrolyte-associated monomers (RB p 2-,rhomboids).FIGURE 2.(a)Normalized average absorption spectra of self-as-sembled arrays with 6,12,18,and 24FL/PDDA bilayers.Inset:Absorbance at the maximum as a function of the number of bilayers.The error bars represent the absorbances at different positions on the same sample,and the solid line corresponds to the linear regression through the origin of coordinates.(b)Normalized spec-trum of FL in aqueous alkaline solution (solid line)and ﬁtted (circles)by linear combination of Gaussian functions (dotted lines).(c)Normalized spectrum of a self-assembled array with FL (solid line)and ﬁtted (circles)by linear combination of the same Gaussian functions as in b,37nm red-shifted and 35%widened (dotted lines).1558VOL.2•NO.6•1556–1560•2010case,the dye is partially dissolved when theﬁlm is inmersed into the polyelectrolyte solution,especially at higher PDDA concentrations,pointing to an intrinsic instability of the assembly(13).Furthermore,at lower dye or polyelectrolyte concentrations,ﬁlms do not grow.Therefore,very narrow concentration ranges are compatible with stableﬁlm forma-tion.Although the charge of PDDA does not depend on the pH of the medium,the investigated xanthene dyes are protonated upon pH reduction,yielding monoanionic,neu-tral,and even monocationic species that are not suitable for self-assembly.On the other hand,hydroxyl ions inhibit FL incorporation,imposing an upper pH limit.Increasing the ionic strength with bases,acids,or salts induces coiling of the polyelectrolite in solution and in theﬁlm,renderingﬁlms with quite different properties(25).Experiments in Solution.To gain further under-standing on the self-assembly process,we carried out a systematic study in aqueous media by adding PDDA to a cell containing a solution of the dye,and measuring the absorp-tion andﬂuorescence spectra for different P/D ratios.Ex-periments carried out by reversing the addition sequence, i.e.,adding the dye to a solution of PDDA,reproduced the previously obtained results,thus revealing that the adsorp-tion equilibrium is readily achieved.In the case of RB,incorporation of the dye into the polyelectrolyte matrix occurs quantitatively at low PDDA concentrations building up aggregates up to P/D)2.In this point,the charges of the dye and the polymer are fully compensated.Further addition of polyelectrolyte causes deaggregation of the dye,which remains associated with PDDA in the dianionic form.The incorporation and further deaggregation remain unaffected in a wide pH range,from 8to11(17).Figure3summarizes the results of subsequent additions of PDDA to a7.6×10-7M aqueous RB solution. The molar fractions of each species were obtained by the analysis of the absorption andﬂuorescence spectra(for further details,see the Supporting Information).The experiments carried out with FL in aqueous alkaline solution reveal a contrasting behavior,as compared with RB. As can be noticed from the speciation diagrams shown in Figure4,at pH∼10and∼12an equilibrium between the dye in the aqueous phase and the PDDA matrix is estab-lished.The incorporation of FL sets in at higher P/D ratios than those found for RB and occurs in the monomeric dianionic form,without evidence of aggregation.The in-crease in pH has a negative effect upon incorporation,just as inﬁlm formation,revealing a competition between the anionic dye and the hydroxyl anions for the cationic adsorp-tion sites in the polyelectrolyte.The behavior of RB and FL is consistent with the differ-ence in aggregation tendencies in solution.For RB,aggrega-tion in water is mainly determined by hydrophobic interac-tions and the value of the dimerization constant is250M-1. On the other hand,FL shows a50times smaller tendency toward dimer formation,which is otherwise predominantly related to hydrogen bonding(26).Charge compensation and free rotation of the monomers within the polyelectrolyte are factors that enhance hydrophobic interactions of RB in water solution,inducing dye aggregation and folding of the poly-electrolyte chain(17).In the case of FL,its displacement by hydroxyl anions evidences a weaker interaction with PDDA, which results in a less extended incorporation into the polyelectrolyte chain and incomplete charge compensation, hampering polyelectrolyte folding. CONCLUSIONSThe unfolded conformation of PDDA within the bilayers (17)provides uniformly distributed charged sites for the adsorption of the dye.The resulting high degree of organiza-tion markedly reduces the formation of RB aggregates, which actually make up to55%of the dye at an effective concentration near1M.At the same P/D ratio,aggregation is massive in solution.These characteristics of the material allow the emission ofﬂuorescence(17)and1O2generation owing to the presence of monomeric dye but do not entirely avoid energy trapping.FL-basedﬁlms,on the other hand, Scheme1.Correlation among Structural and Physicochemical PropertiesFIGURE4.Speciation diagram of FL in PDDA solution as a function of the P/D ratio:monomer in solution(FL S2-,circles),and polyelectrolyte-associated monomers(FL p2-,triangles)at pH(a)∼10and(b)∼12.LETTER VOL.2•NO.6•1556–1560•20101559do not show aggregation at all but are rather prone to desorption of the dye,which is easily displaced by hydroxyl anions.The need to reach higher P/D ratios for the quantita-tive incorporation of the latter dye in solution is consistent with the higher lability of the corresponding arrays.Scheme 1summarizes the correlations existing between the hydro-phobicity of the dye,its aggregation tendency,and the properties associated with its incorporation into the poly-electrolyte in self-assembled arrays as well as in solution. The more hydrophobic RB displays an extended degree of aggregation if compared with FL,and consequently adds to the stabilization of theﬁlms.Therefore,a higher tendency toward dye aggregation results in greaterﬁlm stability toward dye leakage but increases the probability of energy trapping.Acknowledgment.Funding was obtained from CONICET (PIP0319),ANPCyT(PICT00938),and UBA(UBACyT X202).E.S.R.is a staff member of CONICET.M.M.acknowledges CONICET for a postgraduate fellowship.We are also grateful to Prof.L.De Cola,who kindly allowed the performance of IR phosphorescence measurements in her laboratory. Supporting Information Available:Experimental details (PDF).This material is available free of charge via the Internet at .REFERENCES AND NOTES(1)Dai,Z.;Da¨hne,L.;Donath,E.;Mo¨hwald,H.J.Phys.Chem.B2002,106,11501–11508.(2)van Laar,F.M.P.R.;Holsteyns,F.;Vankelecom,I.F.J.;Smeets,S.;Dehaen,W.;Jacobs,P.A.J.Photochem.Photobiol.A:Chem.2001,144,141–151.(3)Palmisano,G.;Gutie´rrez,M.C.;Ferrer,M.L.;Gil-Luna,M.D.;Augugliaro,V.;Yurdakal,S.;Pagliaro,M.J.Phys.Chem.C2008, 112,2667–2670.(4)DeRosa,M.C.;Crutchley,R.J.Coord.Chem.Rev.2002,233-234,351–371.(5)Lo´pez,S.G.;Worringer,G.;Rodrı´guez,H.B.;San Roma´n,E.Phys.Chem.Chem.Phys.2010,12,2246–2253.(6)Paczkowski,J.;Neckers,D.C.Macromolecules1985,18,1245–1253.(7)Rodrı´guez,H.B.;San Roma´n,E.Ann.N.Y.Acad.Sci.2008,1130,247–252.(8)Iler,R.K.J.Colloid Interface Sci.1966,21,569–594.(9)Decher,G.;Schlenoff,J.B.Multilayer Thin Films.SequentialAssembly of Nanocomposite Materials;Wiley-VCH:Weinheim, Germany,2003.(10)Lvov,Y.;Decher,G.;Sukhorunov,G.Macromolecules1993,26,5396–5399.(11)Calvo,E.J.;Etchenique,R.;Pietrasanta,L.;Wolosiuk,A.Anal.Chem.2001,73,1161–1168.(12)Ariga,K.;Lvov,Y.;Kunitake,T.J.Am.Chem.Soc.1997,119,2224–2231.(13)Linford,M.R.;Auch,M.;Mo¨hwald,H.J.Am.Chem.Soc.1998,120,178–182.(14)Lee,S.-H.;Kumar,J.;Tripathy,ngmuir2000,16,10482–10489.(15)Rousseau,E.;Koetse,M.M.;Van der Auweraer,M.;De Schryver,F.C.Photochem.Photobiol.Sci.2002,1,395–406.(16)Nicol,E.;Moussa,A.;Habib-Jiwan,J.-L.;Jonas,A.M.J.Photochem.Photobiol.A:Chem.2004,167,31–35.(17)Mirenda,M.;Dicelio,L.E.;San Roma´n,E.J.Phys.Chem.B2008,112,12201–12207.(18)Sjo¨back,R.;Nygren,J.;Cubista,M.Spectrochim.Acta,Part A1995,51,L7–L21.(19)Neckers,D.C.J.Photochem.Photobiol.A:Chem.1989,47,1–29.(20)Usui,Y.Chem.Lett.1973,2,743–744.(21)Braun,A.M.;Maurette,M.-T.;Oliveros,E.Technologie Photo-chimique;Presses Polytechniques Romandes:Lausanne,Switzer-land,1986.(22)Wilkinson,F.;Helman,W.P.;Ross,A.B.J.Phys.Chem.Ref.Data1993,22,113–262.(23)Rohatgi,K.K.;Mukhopadhyay,A.K.Photochem.Photobiol.1971,14,551–559.(24)Lopez Arbeloa,I.J.Chem.Soc.,Faraday Trans.1981,2,1725–1733.(25)McAloney,R.A.;Sinyor,M.;Dudnik,V.;Goh,ngmuir2001,17,6655–6663.(26)Valdes-Aguilera,O.;Neckers,D.C.Acc.Chem.Res.1989,22,171–177.AM100195V1560VOL.2•NO.6•1556–1560•。

镍柱纯化蛋白说明书

Instruction ManualProBond TM Purification SystemFor purification of polyhistidine-containing recombinant proteinsCatalog nos. K850-01, K851-01, K852-01, K853-01, K854-01,R801-01, R801-15Version K2 September200425-0006iiTable of ContentsKit Contents and Storage (iv)Accessory Products (vi)Introduction (1)Overview (1)Methods (2)Preparing Cell Lysates (2)Purification Procedure—Native Conditions (7)Purification Procedure—Denaturing Conditions (11)Purification Procedure—Hybrid Conditions (13)Troubleshooting (15)Appendix (17)Additional Protocols (17)Recipes (18)Frequently Asked Questions (21)References (22)Technical Service (23)iiiKit Contents and StorageTypes of Products This manual is supplied with the following products:Product CatalogNo.ProBond™ Purification System K850-01ProBond™ Purification System with Antibodywith Anti-Xpress™ Antibody K851-01with Anti-myc-HRP Antibody K852-01with Anti-His(C-term)-HRP Antibody K853-01with Anti-V5-HRP Antibody K854-01ProBond™ Nickel-Chelating Resin (50 ml) R801-01ProBond™ Nickel Chelating Resin (150 ml) R801-15ProBond™Purification System Components The ProBond™ Purification System includes enough resin, reagents, and columns for six purifications. The components are listed below. See next page for resin specifications.Component Composition Quantity ProBond™ Resin 50% slurry in 20% ethanol 12 ml5X NativePurification Buffer250 mM NaH2PO4, pH 8.02.5 M NaCl1 × 125 ml bottleGuanidinium LysisBuffer6 M Guanidine HCl20 mM sodium phosphate, pH 7.8500 mM NaCl1 × 60 ml bottleDenaturingBinding Buffer8 M Urea20 mM sodium phosphate, pH 7.8500 mM NaCl2 × 125 ml bottlesDenaturing WashBuffer8 M Urea20 mM sodium phosphate, pH 6.0500 mM NaCl2 × 125 ml bottlesDenaturing ElutionBuffer8 M Urea20 mM NaH2PO4, pH 4.0500 mM NaCl1 × 60 ml bottleImidazole 3 M Imidazole,20 mM sodium phosphate, pH 6.0500 mM NaCl1 × 8 ml bottlePurificationColumns10 ml columns 6Continued on next pageivKit Contents and Storage, ContinuedProBond™Purification System with Antibody The ProBond™ Purification System with Antibody includes resin, reagents, and columns as described for the ProBond™ Purification System (previous page) and 50 µl of the appropriate purified mouse monoclonal antibody. Sufficient reagents are included to perform six purifications and 25 Western blots with the antibody.For more details on the antibody specificity, subclass, and protocols for using the antibody, refer to the antibody manual supplied with the system.Storage Store ProBond™ resin at +4°C. Store buffer and columns at room temperature.Store the antibody at 4°C. Avoid repeated freezing and thawing of theantibody as it may result in loss of activity.The product is guaranteed for 6 months when stored properly.All native purification buffers are prepared from the 5X Native PurificationBuffer and the 3 M Imidazole, as described on page 7.The Denaturing Wash Buffer pH 5.3 is prepared from the Denaturing WashBuffer (pH 6.0), as described on page 11.Resin and ColumnSpecificationsProBond™ resin is precharged with Ni2+ ions and appears blue in color. It isprovided as a 50% slurry in 20% ethanol.ProBond™ resin and purification columns have the following specifications:• Binding capacity of ProBond™ resin: 1–5 mg of protein per ml of resin• Average bead size: 45–165 microns• Pore size of purification columns: 30–35 microns• Recommended flow rate: 0.5 ml/min• Maximum flow rate: 2 ml/min• Maximum linear flow rate: 700 cm/h• Column material: Polypropylene• pH stability (long term): pH 3–13• pH stability (short term): pH 2–14ProductQualificationThe ProBond™ Purification System is qualified by purifying 2 mg of myoglobinprotein on a column and performing a Bradford assay. Protein recovery mustbe 75% or higher.vAccessory ProductsAdditionalProductsThe following products are also available for order from Invitrogen:Product QuantityCatalogNo.ProBond™ Nickel-Chelating Resin 50 ml150 mlR801-01R801-15Polypropylene columns(empty)50 R640-50Ni-NTA Agarose 10 ml25 ml R901-01 R901-15Ni-NTA Purification System 6 purifications K950-01 Ni-NTA Purification Systemwith Antibodywith Anti-Xpress™ Antibody with Anti-myc-HRP Antibody with Anti-His(C-term)-HRP Antibodywith Anti-V5-HRP Antibody 1 kit1 kit1 kit1 kitK951-01K952-01K953-01K954-01Anti-myc Antibody 50 µl R950-25 Anti-V5 Antibody 50 µl R960-25 Anti-Xpress™ Antibody 50 µl R910-25 Anti-His(C-term) Antibody 50 µl R930-25 InVision™ His-tag In-gel Stain 500 ml LC6030 InVision™ His-tag In-gelStaining Kit1 kit LC6033Pre-Cast Gels and Pre-made Buffers A large variety of pre-cast gels for SDS-PAGE and pre-made buffers for your convenience are available from Invitrogen. For details, visit our web site at or contact Technical Service (page 23).viIntroductionOverviewIntroduction The ProBond™ Purification System is designed for purification of 6xHis-tagged recombinant proteins expressed in bacteria, insect, and mammalian cells. Thesystem is designed around the high affinity and selectivity of ProBond™Nickel-Chelating Resin for recombinant fusion proteins containing six tandemhistidine residues.The ProBond™ Purification System is a complete system that includespurification buffers and resin for purifying proteins under native, denaturing,or hybrid conditions. The resulting proteins are ready for use in many targetapplications.This manual is designed to provide generic protocols that can be adapted foryour particular proteins. The optimal purification parameters will vary witheach protein being purified.ProBond™ Nickel-Chelating Resin ProBond™ Nickel-Chelating Resin is used for purification of recombinant proteins expressed in bacteria, insect, and mammalian cells from any 6xHis-tagged vector. ProBond™ Nickel-Chelating Resin exhibits high affinity and selectivity for 6xHis-tagged recombinant fusion proteins.Proteins can be purified under native, denaturing, or hybrid conditions using the ProBond™ Nickel-Chelating Resin. Proteins bound to the resin are eluted with low pH buffer or by competition with imidazole or histidine. The resulting proteins are ready for use in target applications.Binding Characteristics ProBond™ Nickel-Chelating Resin uses the chelating ligand iminodiacetic acid (IDA) in a highly cross-linked agarose matrix. IDA binds Ni2+ ions by three coordination sites.The protocols provided in this manual are generic, and may not result in 100%pure protein. These protocols should be optimized based on the bindingcharacteristics of your particular proteins.Native VersusDenaturingConditionsThe decision to purify your 6xHis-tagged fusion proteins under native ordenaturing conditions depends on the solubility of the protein and the need toretain biological activity for downstream applications.• Use native conditions if your protein is soluble (in the supernatant afterlysis) and you want to preserve protein activity.• Use denaturing conditions if the protein is insoluble (in the pellet afterlysis) or if your downstream application does not depend on proteinactivity.• Use hybrid protocol if your protein is insoluble but you want to preserveprotein activity. Using this protocol, you prepare the lysate and columnsunder denaturing conditions and then use native buffers during the washand elution steps to refold the protein. Note that this protocol may notrestore activity for all proteins. See page 14.1MethodsPreparing Cell LysatesIntroduction Instructions for preparing lysates from bacteria, insect, and mammalian cellsusing native or denaturing conditions are described below.Materials Needed You will need the following items:• Native Binding Buffer (recipe is on page 8) for preparing lysates undernative conditions• Sonicator• 10 µg/ml RNase and 5 µg/ml DNase I (optional)• Guanidinium Lysis Buffer (supplied with the system) for preparing lysatesunder denaturing conditions• 18-gauge needle• Centrifuge• Sterile, distilled water• SDS-PAGE sample buffer• Lysozyme for preparing bacterial cell lysates• Bestatin or Leupeptin, for preparing mammalian cell lysatesProcessing Higher Amount of Starting Material Instructions for preparing lysates from specific amount of starting material (bacteria, insect, and mammalian cells) and purification with 2 ml resin under native or denaturing conditions are described in this manual.If you wish to purify your protein of interest from higher amounts of starting material, you may need to optimize the lysis protocol and purification conditions (amount of resin used for binding). The optimization depends on the expected yield of your protein and amount of resin to use for purification. Perform a pilot experiment to optimize the purification conditions and then based on the pilot experiment results, scale-up accordingly.Continued on next page2Preparing Bacterial Cell Lysate—Native Conditions Follow the procedure below to prepare bacterial cell lysate under native conditions. Scale up or down as necessary.1. Harvest cells from a 50 ml culture by centrifugation (e.g., 5000 rpm for5 minutes in a Sorvall SS-34 rotor). Resuspend the cells in 8 ml NativeBinding Buffer (recipe on page 8).2. Add 8 mg lysozyme and incubate on ice for 30 minutes.3. Using a sonicator equipped with a microtip, sonicate the solution on iceusing six 10-second bursts at high intensity with a 10-second coolingperiod between each burst.Alternatively, sonicate the solution on ice using two or three 10-secondbursts at medium intensity, then flash freeze the lysate in liquid nitrogen or a methanol dry ice slurry. Quickly thaw the lysate at 37°C andperform two more rapid sonicate-freeze-thaw cycles.4. Optional: If the lysate is very viscous, add RNase A (10 µg/ml) andDNase I (5 µg/ml) and incubate on ice for 10–15 minutes. Alternatively,draw the lysate through a 18-gauge syringe needle several times.5. Centrifuge the lysate at 3,000 ×g for 15 minutes to pellet the cellulardebris. Transfer the supernatant to a fresh tube.Note: Some 6xHis-tagged protein may remain insoluble in the pellet, and can be recovered by preparing a denatured lysate (page 4) followed bythe denaturing purification protocol (page 12). To recover this insolubleprotein while preserving its biological activity, you can prepare thedenatured lysate and then follow the hybrid protocol on page 14. Notethat the hybrid protocol may not restore activity in all cases, and should be tested with your particular protein.6. Remove 5 µl of the lysate for SDS-PAGE analysis. Store the remaininglysate on ice or freeze at -20°C. When ready to use, proceed to theprotocol on page 7.Continued on next page3Preparing Bacterial Cell Lysate—Denaturing Conditions Follow the procedure below to prepare bacterial cell lysate under denaturing conditions:1. Equilibrate the Guanidinium Lysis Buffer, pH 7.8 (supplied with thesystem or see page 19 for recipe) to 37°C.2. Harvest cells from a 50 ml culture by centrifugation (e.g., 5000 rpm for5 minutes in a Sorvall SS-34 rotor).3. Resuspend the cell pellet in 8 ml Guanidinium Lysis Buffer from Step 1.4. Slowly rock the cells for 5–10 minutes at room temperature to ensurethorough cell lysis.5. Sonicate the cell lysate on ice with three 5-second pulses at high intensity.6. Centrifuge the lysate at 3,000 ×g for 15 minutes to pellet the cellulardebris.Transfer the supernatant to a fresh tube.7. Remove 5 µl of the lysate for SDS-PAGE analysis. Store the remaininglysate on ice or at -20°C. When ready to use, proceed to the denaturingprotocol on page 11 or hybrid protocol on page 13.Note: To perform SDS-PAGE with samples in Guanidinium Lysis Buffer, you need to dilute the samples, dialyze the samples, or perform TCAprecipitation prior to SDS-PAGE to prevent the precipitation of SDS.Harvesting Insect Cells For detailed protocols dealing with insect cell expression, consult the manual for your particular system. The following lysate protocols are for baculovirus-infected cells and are intended to be highly generic. They should be optimized for your cell lines.For baculovirus-infected insect cells, when the time point of maximal expression has been determined, large scale protein expression can be carried out. Generally, the large-scale expression is performed in 1 liter flasks seeded with cells at a density of 2 × 106 cells/ml in a total volume of 500 ml and infected with high titer viral stock at an MOI of 10 pfu/cell. At the point of maximal expression, harvest cells in 50 ml aliquots. Pellet the cells by centrifugation and store at -70°C until needed. Proceed to preparing cell lysates using native or denaturing conditions as described on the next page.Continued on next page4Preparing Insect Cell Lysate—Native Condition 1. Prepare 8 ml Native Binding Buffer (recipe on page 8) containingLeupeptin (a protease inhibitor) at a concentration of 0.5 µg/ml.2. After harvesting the cells (previous page), resuspend the cell pellet in8 ml Native Binding Buffer containing 0.5 µg/ml Leupeptin.3. Lyse the cells by two freeze-thaw cycles using a liquid nitrogen or dryice/ethanol bath and a 42°C water bath.4. Shear DNA by passing the preparation through an 18-gauge needle fourtimes.5. Centrifuge the lysate at 3,000 ×g for 15 minutes to pellet the cellulardebris.Transfer the supernatant to a fresh tube.6. Remove 5 µl of the lysate for SDS-PAGE analysis. Store remaining lysateon ice or freeze at -20°C. When ready to use, proceed to the protocol on page 7.Preparing Insect Cell Lysate—Denaturing Condition 1. After harvesting insect cells (previous page), resuspend the cell pellet in8 ml Guanidinium Lysis Buffer (supplied with the system or see page 19for recipe).2. Pass the preparation through an 18-gauge needle four times.3. Centrifuge the lysate at 3,000 ×g for 15 minutes to pellet the cellulardebris. Transfer the supernatant to a fresh tube.4. Remove 5 µl of the lysate for SDS-PAGE analysis. Store remaining lysateon ice or freeze at -20° C. When ready to use, proceed to the denaturingprotocol on page 11 or hybrid protocol on page 13.Note: To perform SDS-PAGE with samples in Guanidinium Lysis Buffer, you need to dilute the samples, dialyze the samples, or perform TCAprecipitation prior to SDS-PAGE to prevent the precipitation of SDS.Continued on next pagePreparing Mammalian Cell Lysate—Native Conditions For detailed protocols dealing with mammalian expression, consult the manual for your particular system. The following protocols are intended to be highly generic, and should be optimized for your cell lines.To produce recombinant protein, you need between 5 x 106and 1 x 107 cells. Seed cells and grow in the appropriate medium until they are 80–90% confluent. Harvest cells by trypsinization. You can freeze the cell pellet in liquid nitrogen and store at -70°C until use.1. Resuspend the cell pellet in 8 ml of Native Binding Buffer (page 8). Theaddition of protease inhibitors such as bestatin and leupeptin may benecessary depending on the cell line and expressed protein.2. Lyse the cells by two freeze-thaw cycles using a liquid nitrogen or dryice/ethanol bath and a 42°C water bath.3. Shear the DNA by passing the preparation through an 18-gauge needlefour times.4. Centrifuge the lysate at 3,000 ×g for 15 minutes to pellet the cellulardebris. Transfer the supernatant to a fresh tube.5. Remove 5 µl of the lysate for SDS-PAGE analysis. Store the remaininglysate on ice or freeze at -20° C. When ready to use, proceed to theprotocol on page 7.Preparing Mammalian Cell Lysates—Denaturing Conditions For detailed protocols dealing with mammalian expression, consult the manual for your particular system. The following protocols are intended to be highly generic, and should be optimized for your cell lines.To produce recombinant protein, you need between 5 x 106and 1 x 107 cells. Seed cells and grow in the appropriate medium until they are 80–90% confluent. Harvest cells by trypsinization. You can freeze the cell pellet in liquid nitrogen and store at -70°C until use.1. Resuspend the cell pellet in 8 ml Guanidinium Lysis Buffer (suppliedwith the system or see page 19 for recipe).2. Shear the DNA by passing the preparation through an 18-gauge needlefour times.3. Centrifuge the lysate at 3,000 ×g for 15 minutes to pellet the cellulardebris. Transfer the supernatant to a fresh tube.4. Remove 5 µl of the lysate for SDS-PAGE analysis. Store the remaininglysate on ice or freeze at -20° C until use. When ready to use, proceed to the denaturing protocol on page 11 or hybrid protocol on page 13.Note: To perform SDS-PAGE with samples in Guanidinium Lysis Buffer, you need to dilute the samples, dialyze the samples, or perform TCAprecipitation prior to SDS-PAGE to prevent the precipitation of SDS.Purification Procedure—Native ConditionsIntroduction In the following procedure, use the prepared Native Binding Buffer, NativeWash Buffer, and Native Elution Buffer, columns, and cell lysate preparedunder native conditions. Be sure to check the pH of your buffers before starting.Buffers for Native Purification All buffers for purification under native conditions are prepared from the5X Native Purification Buffer supplied with the system. Dilute and adjust the pH of the 5X Native Purification Buffer to create 1X Native Purification Buffer (page 8). From this, you can create the following buffers:• Native Binding Buffer• Native Wash Buffer• Native Elution BufferThe recipes described in this section will create sufficient buffers to perform one native purification using one kit-supplied purification column. Scale up accordingly.If you are preparing your own buffers, see page 18 for recipe.Materials Needed You will need the following items:• 5X Native Purification Buffer (supplied with the system or see page 18 forrecipe)• 3 M Imidazole (supplied with the system or see page 18 for recipe)• NaOH• HCl• Sterile distilled water• Prepared ProBond™ columns with native buffers (next page)• Lysate prepared under native conditions (page 2)Imidazole Concentration in Native Buffers Imidazole is included in the Native Wash and Elution Buffers to minimize the binding of untagged, contaminating proteins and increase the purity of the target protein with fewer wash steps. Note that, if your level of contaminating proteins is high, you may add imidazole to the Native Binding Buffer.If your protein does not bind well under these conditions, you can experiment with lowering or eliminating the imidazole in the buffers and increasing the number of wash and elution steps.Continued on next page1X Native Purification Buffer To prepare 100 ml 1X Native Purification Buffer, combine:• 80 ml of sterile distilled water• 20 ml of 5X Native Purification Buffer (supplied with the system or see page 18 for recipe)Mix well and adjust pH to 8.0 with NaOH or HCl.Native Binding Buffer Without ImidazoleUse 30 ml of the 1X Native Purification Buffer (see above for recipe) for use as the Native Binding Buffer (used for column preparation, cell lysis, and binding).With Imidazole (Optional):You can prepare the Native Binding Buffer with imidazole to reduce the binding of contaminating proteins. (Note that some His-tagged proteins may not bind under these conditions.).To prepare 30 ml Native Binding Buffer with 10 mM imidazole, combine: • 30 ml of 1X Native Purification Buffer• 100 µl of 3 M Imidazole, pH 6.0Mix well and adjust pH to 8.0 with NaOH or HCl.Native Wash Buffer To prepare 50 ml Native Wash Buffer with 20 mM imidazole, combine:• 50 ml of 1X Native Purification Buffer• 335 µl of 3 M Imidazole, pH 6.0Mix well and adjust pH to 8.0 with NaOH or HCl.Native Elution Buffer To prepare 15 ml Native Elution Buffer with 250 mM imidazole, combine:• 13.75 ml of 1X Native Purification Buffer• 1.25 ml of 3 M Imidazole, pH 6.0Mix well and adjust pH to 8.0 with NaOH or HCl.Continued on next pageDo not use strong reducing agents such as DTT with ProBond™ columns. DTTreduces the nickel ions in the resin. In addition, do not use strong chelatingagents such as EDTA or EGTA in the loading buffers or wash buffers, as thesewill strip the nickel from the columns.Be sure to check the pH of your buffers before starting.PreparingProBond™ ColumnWhen preparing a column as described below, make sure that the snap-off capat the bottom of the column remains intact. To prepare a column:1. Resuspend the ProBond™ resin in its bottle by inverting and gentlytapping the bottle repeatedly.2. Pipet or pour 2 ml of the resin into a 10-ml Purification Columnsupplied with the kit. Allow the resin to settle completely by gravity(5-10 minutes) or gently pellet it by low-speed centrifugation (1 minuteat 800 ×g). Gently aspirate the supernatant.3. Add 6 ml of sterile, distilled water and resuspend the resin byalternately inverting and gently tapping the column.4. Allow the resin to settle using gravity or centrifugation as described inStep 2, and gently aspirate the supernatant.5. For purification under Native Conditions, add 6 ml Native BindingBuffer (recipe on page 8).6. Resuspend the resin by alternately inverting and gently tapping thecolumn.7. Allow the resin to settle using gravity or centrifugation as described inStep 2, and gently aspirate the supernatant.8. Repeat Steps 5 through 7.Storing PreparedColumnsTo store a column containing resin, add 0.02% azide or 20% ethanol as apreservative and cap or parafilm the column. Store at room temperature.Continued on next pagePurification Under Native Conditions Using the native buffers, columns and cell lysate, follow the procedure below to purify proteins under native conditions:1. Add 8 ml of lysate prepared under native conditions to a preparedPurification Column (page 9).2. Bind for 30–60 minutes using gentle agitation to keep the resinsuspended in the lysate solution.3. Settle the resin by gravity or low speed centrifugation (800 ×g), andcarefully aspirate the supernatant. Save supernatant at 4°C forSDS-PAGE analysis.4. Wash with 8 ml Native Wash Buffer (page 8). Settle the resin by gravityor low speed centrifugation (800 ×g), and carefully aspirate thesupernatant. Save supernatant at 4°C for SDS-PAGE analysis.5. Repeat Step 4 three more times.6. Clamp the column in a vertical position and snap off the cap on thelower end. Elute the protein with 8–12 ml Native Elution Buffer (seepage 2). Collect 1 ml fractions and analyze with SDS-PAGE.Note: Store the eluted fractions at 4°C. If -20°C storage is required, addglycerol to the fractions. For long term storage, add protease inhibitors to the fractions.If you wish to reuse the resin to purify the same recombinant protein, wash the resin with 0.5 M NaOH for 30 minutes and equilibrate the resin in a suitable binding buffer. If you need to recharge the resin, see page 17.Purification Procedure—Denaturing ConditionsIntroduction Instructions to perform purification using denaturing conditions with prepareddenaturing buffers, columns, and cell lysate are described below.Materials Needed You will need the following items:• Denaturing Binding Buffer (supplied with the system or see page 19 forrecipe)• Denaturing Wash Buffer, pH 6.0 (supplied with the system or see page 19 forrecipe) and Denaturing Wash Buffer, pH 5.3 (see recipe below)• Denaturing Elution Buffer (supplied with the system or see page 20 forrecipe)• Prepared ProBond™ columns with Denaturing buffers (see below)• Lysate prepared under denaturing conditions (page 11)Preparing the Denaturing Wash Buffer pH 5.3 Using a 10 ml aliquot of the kit-supplied Denaturing Wash Buffer (pH 6.0), mix well, and adjust the pH to 5.3 using HCl. Use this for the Denaturing Wash Buffer pH 5.3 in Step 5 next page.Be sure to check the pH of your buffers before starting. Note that thedenaturing buffers containing urea will become more basic over time. PreparingProBond™ ColumnWhen preparing a column as described below, make sure that the snap-off capat the bottom of the column remains intact.If you are reusing the ProBond™ resin, see page 17 for recharging protocol.To prepare a column:1. Resuspend the ProBond™ resin in its bottle by inverting and gentlytapping the bottle repeatedly.2. Pipet or pour 2 ml of the resin into a 10-ml Purification Columnsupplied with the kit. Allow the resin to settle completely by gravity(5-10 minutes) or gently pellet it by low-speed centrifugation (1 minuteat 800 ×g). Gently aspirate the supernatant.3. Add 6 ml of sterile, distilled water and resuspend the resin byalternately inverting and gently tapping the column.4. Allow the resin to settle using gravity or centrifugation as described inStep 2, and gently aspirate the supernatant.5. For purification under Denaturing Conditions, add 6 ml of DenaturingBinding Buffer.6. Resuspend the resin by alternately inverting and gently tapping thecolumn.7. Allow the resin to settle using gravity or centrifugation as described inStep 2, and gently aspirate the supernatant. Repeat Steps 5 through 7.Continued on next pagePurification Procedure—Denaturing Conditions, ContinuedPurification Under Denaturing Conditions Using the denaturing buffers, columns, and cell lysate, follow the procedure below to purify proteins under denaturing conditions:1. Add 8 ml lysate prepared under denaturing conditions to a preparedPurification Column (page 11).2. Bind for 15–30 minutes at room temperature using gentle agitation (e.g.,using a rotating wheel) to keep the resin suspended in the lysatesolution. Settle the resin by gravity or low speed centrifugation (800 ×g), and carefully aspirate the supernatant.3. Wash the column with 4 ml Denaturing Binding Buffer supplied with thekit by resuspending the resin and rocking for two minutes. Settle theresin by gravity or low speed centrifugation (800 ×g), and carefullyaspirate the supernatant. Save supernatant at 4°C for SDS-PAGEanalysis. Repeat this step one more time.4. Wash the column with 4 ml Denaturing Wash Buffer, pH 6.0 supplied inthe kit by resuspending the resin and rocking for two minutes. Settle the resin by gravity or low speed centrifugation (800 ×g), and carefullyaspirate the supernatant. Save supernatant at 4°C for SDS-PAGEanalysis. Repeat this step one more time.5. Wash the column with 4 ml Denaturing Wash Buffer pH 5.3 (see recipeon previous page) by resuspending the resin and rocking for 2 minutes.Settle the resin by gravity or low speed centrifugation (800 ×g), andcarefully aspirate the supernatant. Save supernatant at 4°C for SDS-PAGE analysis. Repeat this step once more for a total of two washes with Denaturing Wash Buffer pH 5.3.6. Clamp the column in a vertical position and snap off the cap on thelower end. Elute the protein by adding 5 ml Denaturing Elution Buffersupplied with the kit. Collect 1 ml fractions and monitor the elution bytaking OD280readings of the fractions. Pool the fractions that contain the peak absorbance and dialyze against 10 mM Tris, pH 8.0, 0.1% Triton X-100 overnight at 4°C to remove the urea. Concentrate the dialyzedmaterial by any standard method (i.e., using 10,000 MW cut-off, low-protein binding centrifugal instruments or vacuum concentrationinstruments).If you wish to reuse the resin to purify the same recombinant protein, wash the resin with 0.5 M NaOH for 30 minutes and equilibrate the resin in a suitable binding buffer. If you need to recharge the resin, see page 17.。

《环境功能材料及其表征技术》课件

Aggregation occurs when there is a net attraction and an equilibrium separation between the components
Whitesides G. M., Boncheva M. PNAS 2002;99:4769-4774 Copyright ©2002, The National Academy of Sciences
Self-Assembly
• Self-assembly is a process in which components, either separate or linked, spontaneously form ordered aggregates. • Self-assembly can occur with components having sizes from the molecular to the macroscopic, provided that appropriate conditions are met.
STM image of dodecanethiol on gold(111) prepared by adsorption from a millimolar solution of dodecanethiol in ethanol
Assembly of DNA Monolayers
STM of Self-Assembled Monolayer
Importance of Self-Assembly
First: it is centrally important in life. The cell contains an astonishing range of complex structures such as lipid membranes, folded proteins, structured nucleic acids, protein aggregates, molecular machines, and many others that form by self-assembly. Second: self-assembly provides routes to a range of materials with regular structures: molecular crystals, liquid crystals, and semicrystalline and phase-separated polymers are examples. Third: self-assembly also occurs widely in systems of components larger than molecules, and there is great potential for its use in materials and condensed matter science. Fourth: self-assembly seems to offer one of the most general strategies now available for generating nanostructures.

超分子自组装

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Supramolecular Amphiphiles
超分子两亲分子
主--客体相互作用
电荷转移相互作用
氢键配位键
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Supramolecular Amphiphiles
偶氮苯与α-环糊精的主-客体相互作用
反式，低能态
顺式，高能态
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Self-assembled Monolayers

自组装膜（ Self-assembled Monolayers ）
自组装膜是活性分子通过自发吸附在基底上生成的有序分子膜具有取向性好、排列紧密、结构稳定等特点广泛应用于金属防腐、材料科学、医学等领域

相对传统有lf-assembly
Apr，18, 2012
Outline
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Supramolecular Amphiphiles Self-assembled Monolayers Layer-by-Layer Assembly
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Supramolecular Amphiphiles
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Self-assembled Monolayers
软刻蚀（ Soft lithography ）
制作刚性硬模板
浇铸预聚物 PDMS
Au/Ti
固化后剥离 PDMS
SAM
图 1 PDMS模板的加工
图 2 微接触印刷过程

软刻蚀是一类基于自组装和复制模塑等原理的非光刻微米和纳米加工方法技术环节主要分为弹性模板/印章的制作、微接触印刷成膜等步骤目前, 软刻蚀技术的研究还处于初步探索阶段, 发展前景非常广阔，能够应用于微电子、微光学、生物技术等领域施雷庭老师小组内部交流

铝合金表面原位自组装超疏水膜层的制备及耐蚀性能_李松梅

铝合金表面原位自组装超疏水膜层的制备及耐蚀性能李松梅*周思卓刘建华(北京航空航天大学材料科学与工程学院,空天材料与服役教育部重点实验室,北京100191)摘要：采用阳极氧化法在铝合金表面原位构造粗糙结构,经表面自组装硅氧烷后得到超疏水自清洁表面,与水滴的接触角最大可达157.5°±2.0°,接触角滞后小于3°.通过傅立叶变换红外(FT -IR)光谱分析仪、场发射扫描电子显微镜(FE -SEM)、能谱仪(EDS)、原子力显微镜(AFM)和接触角测试对阳极氧化电流密度、硅氧烷溶液中水的含量和自组装时间等参数进行了分析,并得到制备超疏水自清洁表面的最优工艺参数.FE -SEM 及AFM 的测试结果表明,由自组装硅氧烷膜层的无序性形成的纳米结构和阳极氧化构造的微米级粗糙结构与硅氧烷膜层的低表面能的协同作用构成了稳定的超疏水表面.电化学测试(动电位极化)的结果表明,原位自组装超疏水膜层极大地提高了铝合金的耐蚀性.关键词：超疏水;原位;自组装;硅氧烷;耐蚀性中图分类号：O647;O646Fabrication and Anti -Corrosion Property of In situ Self -AssembledSuper -Hydrophobic Films on Aluminum AlloysLI Song -Mei *ZHOU Si -ZhuoLIU Jian -Hua(Key Laboratory of Aerospace Materials and Performance of the Ministry of Education,School of Materials Science and Engineering,Beihang University,Beijing 100191,P.R.China )Abstract ：In situ rough structures on an aluminum alloy were formed by anodic oxidation method.After siloxane self -assembly on the rough structures,super -hydrophobic and self -cleaning films were fabricated.The static contact angle of the super -hydrophobic surface with a water drop was 157.5°±2.0°at its maximum and the contact angle hysteresis was less than 3°.The influence of anodic oxidation current density,the water content of the siloxane solution,and self -assembly time on film formation were studied by Fourier transform infrared (FT -IR)spectroscopy,field emission scanning electron microscopy (FE -SEM),energy dispersive spectroscopy (EDS),atomic force microscopy (AFM)and contact angle measurements.Optimum parameters to fabricate the super -hydrophobic surface were obtained.FE -SEM and AFM results indicated that microstructures were obtained by anodic oxidation and nanostructures were obtained by the disorder of self -assembly film.Stable super -hydrophobic surfaces were produced by the cooperation of micro/nano -structures and the low surface free energy of the siloxane films.The electrochemical measurement (potentiodynamic polarization)indicated that the anti -corrosion property of the aluminum alloy was greatly improved by the in situ super -hydrophobic film.Key Words ：Super -hydrophobic;In situ ;Self -assembly;Siloxane;Anti -corrosion property[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .,2009,25(12)：2581-2589近年来,超疏水表面的制备及应用引起了人们很大的关注[1-3].超疏水表面是指水滴的静态接触角(static contact angle,θS )大于150°的表面[4],其中滚动角小于10°的表面为自清洁表面.自然界中有很多超疏水自清洁表面,如荷叶[5],一些昆虫的翅或腿[6,7],水滴不容易湿润这些表面,而且很容易滚落,同时带December Received:July 15,2009;Revised:September 14,2009;Published on Web:November 3,2009.*Corresponding author.Email:Songmei_li@;Tel:+86-10-82317103.The project was supported by the Aero -Science Fund,China (2007ZF51066).航空科学基金(2007ZF51066)资助项目鬁Editorial office of Acta Physico -Chimica Sinica2581Acta Phys.-Chim.Sin.,2009Vol.25走表面的污物,从而达到自清洁的效果.这种现象被称为荷叶效应.Barthlott等[8]进行对荷叶表面研究,发现其表面微小的柱状突起构成的粗糙结构和表面的疏水性蜡质的协同作用是造成其表面具有特殊湿润性能的原因.随后,Jiang等[9]提出荷叶表面存在的微米-纳米的分等级的粗糙结构使得与水滴接触的表面孔隙中存在空气,增大了表观接触角,减小了接触角滞后(contact angle hysteresis,CAH=θadv-θrec,其中θadv为前进接触角,θrec为后退接触角),最终造成超疏水自清洁现象.人工超疏水表面的制备一直以来都是以模仿荷叶效应作为手段,即在疏水性材料表面构造粗糙结构[10-12]或对粗糙表面进行疏水性处理[13-17],衍生出很多独特的制备方法.这些方法制备的超疏水表面虽然疏水性能优异,但在很多领域之所以还没有成功的应用,主要原因在于其综合性能均有或多或少的缺陷,所以改进制备方法,提高超疏水表面的综合性能是其走向实际应用的第一步.在诸多制备超疏水表面的方法中,模板法的工艺成熟且成本相对较低,有很大的发展空间.模板法主要采用纯铝的多孔阳极氧化膜作为模板,在对聚合物进行热挤压成型后构造超疏水表面[18-20].但是,此方法得到的聚合物膜由于其与基体的结合力差、施工困难等缺陷,往往难于应用到金属表面.如果在零件上原位制备超疏水膜层则解决了以上难点.在金属基体上制备的超疏水自清洁表面不仅能够使其获得装饰效果,而且自清洁性能避免了腐蚀介质与金属的长时间接触,从而极大地提高了金属的耐腐蚀性能[21,22].本文即采用具有诸多优异性能的在现代日用、工业上应用最多的LY12铝合金作为制备超疏水表面的基体材料,对其表面进行阳极氧化后自组装低表面能的聚硅氧烷膜层,通过表面粗糙结构以及低表面能材料的协同作用在铝合金表面原位制备了超疏水自清洁表面.此外,硅氧烷水解后可以在阳极氧化铝合金表面形成强的化学键,保证了聚硅氧烷膜层与基体之间具有很好的结合力[23,24];而且,通过缩聚形成的硅氧网络的高键能使硅氧烷基聚合物具有良好的热稳定性[25].铝合金阳极氧化工艺不仅能在铝合金表面构造粗糙结构,而且还能够增加基体的耐蚀性,同时原位生长的方式使得超疏水结构与基体之间具有良好结合力.1实验部分1.1试剂材料LY12CZ航空铝合金板材切割为尺寸60mm×40mm×2mm,其成分列于表1.十二氟庚基丙基三甲氧基硅烷(G502,雪佳氟硅化学有限公司);甲醇,硫酸及氯化钠(分析纯,北京化工厂);十八水合硫酸铝(分析纯,天津市福晨化学试剂厂).1.2试样前处理LY12CZ铝合金首先经NaOH(40g·L-1)溶液除去表面包铝层;水磨砂纸打磨至1000#,去离子水超声波清洗10min;基体随后采用NaOH(40g·L-1)在60℃下碱洗2min,室温下采用三酸出光液(CrO3/ HNO3/HF)出光1min,去离子水清洗等处理后备用.1.3铝合金阳极氧化预处理后的LY12CZ铝合金采用硫酸恒电流阳极氧化工艺,硫酸浓度为180g·L-1,溶液中Al3+离子的浓度为10g·L-1,控制温度为30℃,控制电流密度在1.00至8.00A·dm-2之间,阳极氧化2h后得到不同粗糙结构的表面.阳极氧化后的试样经去离子水冲洗数次,以去除表面残留的溶液,立即进行下一步处理.1.4自组装低表面能材料修饰表面配制总体积100mL不同摩尔比例的甲醇及去离子水溶液,滴加G502并控制浓度为0.01mol·L-1, 30℃下磁力搅拌,老化2h,溶液呈半透明的乳白色.将阳极氧化后或预处理后的试样浸入该溶液中,恒温水浴30℃反应若干小时后取出.去离子水洗数次以去除表面未反应的小分子和溶剂,80℃下固化1 h后获得的试样进行下一步测试.1.5膜层性能的测试及表征试样表面粗糙结构的表征采用场发射扫描电镜FE-SEM(Hitachi S-4800SEM).采用能谱仪EDS (Hitachi S-530,Oxford Link2SISI)和傅立叶变换红外光谱分析仪FT-IR(Avatar-360,Nicolet)分别分析试样表面元素组成和低表面能聚合物与表面的键合情表1LY12CZ铝合金名义成分(w,质量分数)Table1Nominal chemical components of aluminum alloy LY12CZ(w,mass fraction) Element Cu Mg Fe Mn Si Zn Ti Cr others Alw(%) 3.8-4.9 1.2-1.80.500.30-0.900.500.250.150.100.15balance 2582No.12李松梅等：铝合金表面原位自组装超疏水膜层的制备及耐蚀性能况.在FE-SEM及EDS测试前试样表面喷金30s以确保具有良好的导电性.采用原子力显微镜AFM(MultiMode Nanoscope IIIa,Veeco Instruments Ins.)分析试样微区的表面形貌;测试采用轻敲模式(Tapping Mode),测试区域为5μm×5μm,扫描速率为10μm·s-1.表面与水滴的静态接触角及动态接触角测试采用Dataphysics OCA20接触角测试仪,测试均在室温下进行;滴液管缓慢地将2μL去离子水滴放在试样表面,得到静态接触角θS;动态接触角测试首先在试样表面滴加1μL水滴后,以1μL·s-1的滴加速度滴加至5μL,接触角增加至基本恒定且液滴即将滚动时测试得到的接触角为前进接触角θadv;相应的,将水滴吸入滴液管至液滴恰好离开试样表面或接触角恒定时测得的接触角为后退接触角θrec.接触角测试均选取试样表面5个以上不同点的测量结果的平均值作为接触角值.动电位极化曲线测试采用三电极体系,只经前处理的铝合金、阳极氧化后的铝合金和自组装超疏水膜层后的铝合金分别作为研究电极,铂丝电极为辅助电极,饱和甘汞电极(SCE)为参比电极,采用3.5% (w)的NaCl水溶液作为介质.测试采用电化学工作站(PARSTAT2273,Ametek,American),测试软件为PowerSuite测试系统,试样测试面积为7cm2,扫描速率为3mV·s-1.2结果与讨论2.1阳极氧化电流密度对表面湿润性的影响通过控制铝合金阳极氧化电流密度在1.00-8.00A·dm-2区间内制备了一系列不同粗糙结构的表面,经自组装十二氟庚基丙基三甲氧基硅烷(G502)后,得到了电流密度与2μL去离子水滴在表面的静态接触角及接触角滞后的关系曲线,如图1所示.在讨论电流密度的影响时,自组装G502溶液浓度固定为0.01mol·L-1,每100mL溶液中水的含量为3.7mol,自组装时间固定为4h.未经阳极氧化的铝合金表面自组装G502后得到几乎理想的光滑表面,与水滴的静态接触角θS=110.2°±1.0°,接触角滞后CAH>19°.当阳极氧化电流密度小于2.00A·dm-2时,静态接触角随电流密度的增加迅速增大,接触角滞后迅速降低.当电流密度在2.00至3.00 A·dm-2范围内时,静态接触角均大于150°,表面呈超疏水状态,且接触角滞后很小.电流密度在3.00至8.00A·dm-2范围内时,静态接触角均在150°附近,而接触角滞后略有上升.通过图1中接触角变化趋势的示意曲线分析得到,试样表面由疏水性向超疏水性的转变在2.00A·dm-2附近很窄的电流密度区间内发生.为了得到最优的电流密度参数,在1.00至3.00A·dm-2区间内依次在多个电流密度下制备了疏水表面,并测试了与水滴的静态接触角,电流密度及测试的接触角值的结果见表2.由表2可以得到当电流密度为2.25A·dm-2时,静态接触角达到最大,θS=157.5°±2.0°,并且经动态接触角测试,接触角滞后小于3°.图2为在电流密度2.25A·dm-2下制备的超疏水表面与水滴的接触照片及接触角测试照片.从图2(a,b)中可以清楚看出,水滴在其表面的静态接触角很大,且试样稍有倾斜或外加微小的扰动,水滴会表2不同电流密度制备的疏水表面与水滴的静态接触角及标准误差Table2Static contact angles and standard deviations(SD)of hydrophobic surfaces fabricatedwith different current densities图1水滴在试样表面的静态接触角(θS)及接触角滞后(CAH)与阳极氧化电流密度(I)的关系曲线Fig.1Dependence of static contact angle(θS)and contact angle hysteresis(CAH)of the water droplets on the surfaces on the current density(I)of anodicoxidationI/(A·dm-2)θS/(°)SD(°)1.00138.3 4.31.25131.4 4.91.50146.0 1.11.75144.9 1.42.00153.9 6.12.25157.5 2.02.50151.90.72.75154.1 2.13.00153.7 3.02583Acta Phys.-Chim.Sin.,2009Vol.25图3阳极氧化铝合金表面的FE -SEM 照片Fig.3FE -SEM images of the surface of anodized aluminum alloy(a,b)FE -SEM images with different amplified parameters of anodized film (current density:2.25A ·dm -2)without G502(dodecafluoroheptyl -propyl -trimethoxylsilane)self -assembly;(c-h)FE -SEM images with different amplified parameters of anodized films at different anodic current densities of1.00A ·dm -2(c,d),2.25A ·dm -2(e,f),and 8.00A ·dm -2(g,h)after G502self -assembly迅速滚落.图2d 显示出滴管上的水滴不会由于超疏水表面的粘滞作用而脱落,说明超疏水表面的接触角滞后非常小,具有优异的自清洁性能.铝合金在不同阳极氧化电流密度下的表面形貌见图3.由一定电流密度下制备的阳极氧化表面自组装G502前(图3(a,b))与自组装G502后(图3(e,f))对比可知,自组装膜层对阳极氧化表面微米尺度的形貌没有影响.不同电流密度下制备的阳极氧化膜层的表面形貌(如图3(c,e,g)所示)表明,阳极氧化电流密度的变化直接决定了表面的微观形貌,所以图2水滴在试样表面的状态照片及轮廓图Fig.2Photographs and profiles of the water droplets on the surfaces(a)digital photo of the water drops on super -hydrophobic surface;(b)profile of water droplet on super -hydrophobic surface;(c)profile of water droplet on the surface of anodized aluminum alloy without G502self -assembly;(d)behavior of water droplet on the super -hydrophobic surface(the directions of the arrowheads were the movements of the surfaces)2584No.12李松梅等：铝合金表面原位自组装超疏水膜层的制备及耐蚀性能图4不同阳极氧化电流密度下经自组装G502后铝合金表面形貌的AFM照片Fig.4AFM images of the surfaces at different anodic current densities after G502self-assemblyI/(A·dm-2):(a)1.00,(b)2.25,(c)8.00;scanning area:5μm×5μm在讨论阳极氧化对表面形貌的影响时,自组装膜层的影响可以忽略.由图3(c,d,e,f)可知,在1.00、2.25A·dm-2电流密度下,铝合金表面形成了致密粗糙的氧化层,且2.25A·dm-2电流密度下生成的氧化层比1.00A·dm-2下沟壑更深且宽,粗糙度更大.由图3(e,f,g,h)可看出,电流密度为8.00A·dm-2时制备的表面出现了10μm数量级的较宽沟壑,且在高倍下的表面形貌对比(图3(f,h))也显示出电流密度为8.00A·dm-2时比2.25A·dm-2时制备的表面沟壑密度更大,具有更大的粗糙度.采用AFM对不同阳极氧化电流密度下制备的氧化膜表面形貌及粗糙度进行分析,结果如图4所示,从图中可以看出随着电流密度增大,表面起伏增大,与FE-SEM照片的结果一致.随着阳极氧化电流密度的增大,表面形貌发生改变,表面粗糙度增大.表面形貌的变化直接影响了表面湿润性.接触角测试及表面形貌的结果表明,随着电流密度的增大,表面粗糙结构发生了变化.当阳极氧化电流密度小于2.00A·dm-2时,接触角随着电流密度的增加———即粗糙度的增加———而增大,水滴在其表面呈Wenzel态[26,27],cosθr=r cosθ0(1)其中θ0为液滴与光滑表面的杨氏接触角,θr为液滴与真实粗糙表面的表观接触角,r为试样真实表面积与表观面积的比值,且r>1.水滴在表面显示出大的接触角滞后,是由于表面的微观沟壑深度较浅,水滴由于自身重力进入到沟壑内,完全湿润了固体表面并形成了连续的固液接触线,在表面的钳制作用下,三相接触线在较小的能量下不能移动[28].当阳极氧化电流密度在2.00A·dm-2附近时,表面沟壑较深.由于水滴与试样表面接触时存在毛细作用,表面微观沟壑中存留有空气,所以其接触面为三相接触界面,即水滴在试样表面呈Cassie-Baxter态[29-31], cosθf=f SL cosθ0-1+f SL(2)其中,θf为液滴与真实粗糙表面的表观接触角,fSL为液滴固相接触面积占总投影面积的比例,fSL≤1.根据Cassie-Baxter方程,随着fSL的减小,表观接触角迅速增大,同时接触角滞后迅速减小,表面呈超疏水状态.当电流密度更大时,基体局部出现了较快的溶解,出现了更大更宽的孔隙,液滴因自身重力容易渗入孔隙中,从而减小了静态接触角,增大了接触角滞后.2.2自组装低表面能材料对表面湿润性的影响未经自组装G502的阳极氧化铝合金表面为亲水表面,与水滴的接触角几乎为0°(图2c),而阳极氧化铝合金表面经自组装G502膜层后可达到超疏水性能.因此,在粗糙表面自组装低表面能的硅氧烷是获得超疏水性能的关键之一.本节中首先对阳极氧化铝合金表面的自组装G502膜层进行了表征,随后讨论了自组装溶液的含水量和自组装时间对湿润性能的影响.为了保证自组装前表面粗糙结构的一致性,阳极氧化电流密度均控制为2.25A·dm-2,阳极氧化的其他参数不变.2.2.1自组装膜层的结构及组成的表征阳极氧化铝合金表面自组装膜层采用FT-IR谱及EDS表征.由FT-IR谱(图5)可知,阳极氧化铝合金经自组装十二氟庚基丙基三甲氧基硅烷(G502)得到的超疏水表面在1249cm-1的吸收峰为—CF2和—CF3基团中C—F键的伸缩振动峰,在2854cm-1的吸收峰为C—H键的伸缩振动吸收峰[32],说明自2585Acta Phys.-Chim.Sin.,2009Vol.25组装G502在氧化铝膜表面含有大量—CF3和—CF2以及—CH2等疏水基团,这些向外伸展的疏水基团是构成低自由能表面的关键.G502发生水解和缩聚反应,生成聚硅氧烷,即形成Si—O—Si键,但由于其吸收峰的位置(约为1100cm-1)与氧化铝的红外光谱位置相近,且测试样品中自组装膜含量小,Si—O—Si键的伸缩振动峰并不明显[24,33].超疏水表面的EDS分析(图6)说明表面存在C、O、F、Al和Si等元素,进一步证实了在阳极氧化铝合金表面经G502处理后存在聚硅氧烷分子层.铝合金表面的聚硅氧烷膜层不仅降低了表面自由能,而且由于硅氧烷在氧化铝合金表面的生长方式不同从而形成了具有纳米等级的粗糙结构.铝合金在2.25A·dm-2电流密度下阳极氧化后自组装G502前后的表面形貌如图7所示.无论是否存在自组装膜层,其表面微米级尺度上均存在形貌相近的沟壑,构成了微米等级的粗糙结构.图7(a,b)中局部放大照片的对比显示,自组装G502后的表面在微米等级的“平台”上存在纳米等级的粗糙结构;未经自组装G502的表面“平台”相对光滑,不存在纳米等级的粗糙结构.AFM对微区的表面形貌分析(图4)表明,表面自组装膜层构成了纳米级结构.阳极氧化铝合金微米级粗糙表面的自组装膜层形成的纳米级结构主要是由于G502在氧化物表面存在多种反应机制.含有大量—CF3、—CF2、—CH2等疏水基团的G502经水解后,生成具有三个—OH 活性基团的硅醇(—Si—OH),与阳极氧化铝合金表面富集的—OH基团(—Al—OH)反应脱去H2O分子,通过共价键与基体键合(—Al—O—Si—),含氟的长碳链则向外伸展.G502在溶液中水解后,在富含活性基团的氧化铝合金表面可能发生多种类型的反应,如存在残留—Si—OH的小分子聚合物与基体表面的键合,—Si—OH间的横向缩合或纵向缩合形成接枝聚硅氧烷[34],见图8,这些互相竞争的反应导致了分子膜层的无序性,从而构成了独特的纳米级结构[33,35].这些纳米级结构与阳极氧化构成的微米级粗糙结构共同构成了微米-纳米分等级的粗糙结构,从而使超疏水性能更稳定[23,36],即当液滴由Cassie-Baxter态转变为Wenzel态时需要越过更高的能垒.图5铝合金表面阳极氧化膜经G502自组装前后的FT-IR谱Fig.5FT-IR spectra of anodic oxide films ofaluminum alloy before and after G502self-assembly图7阳极氧化铝合金表面自组装G502前(a)后(b)的FE-SEM照片Fig.7FE-SEM images of the surface of anodizedaluminum alloy before(a)and after(b)G502self-assembly图6阳极氧化铝合金表面自组装G502后的能谱Fig.6EDS spectrum of the surface of anodizedaluminum alloy after G502self-assembly2586No.12李松梅等：铝合金表面原位自组装超疏水膜层的制备及耐蚀性能G502在富含—OH的活性表面自组装反应的机制对溶液中水的含量、反应时间、温度、表面活性基团数量等因素很敏感,所以控制反应条件对超疏水表面的制备非常重要[37].本文选取了硅氧烷溶液的含水量及自组装时间作为控制条件,详细讨论了自组装硅氧烷对表面疏水性能的影响.2.2.2自组装溶液的含水量对表面疏水性能的影响经阳极氧化后的试样浸入含水量不同的G502溶液自组装4h得到的表面与水滴的静态接触角关系曲线见图9.当G502的甲醇溶液中不含水时,只有很少量的硅氧烷在甲醇溶液中水解并键合到试样表面,使得低表面能的硅氧烷在试样表面的覆盖率很低,θS=16.9°±5.1°,表面呈亲水性.当每100mL溶液中水的含量小于约3.7mol时,静态接触角随着溶液中水的含量增加而增大;这是由于随着水含量的增加,硅氧烷在溶液中的水解愈加充分,增大了硅氧烷在试样表面的覆盖率,从而增大了疏水性.当每100mL溶液中水的含量约为3.7mol时,试样表面呈超疏水性,静态接触角最大达157.5°±2.0°.当每100mL溶液中水的含量约大于5.3mol时,静态接触角迅速减小,使表面呈弱亲水性,这可能是由于两方面原因:(1)硅氧烷在水中的溶解度很小,在溶液中无法通过扩散与试样表面键合,导致硅氧烷在试样表面覆盖率很低,影响了表面疏水性;(2)由于大量水的存在,硅氧烷水解迅速且容易发生自缩合,从而消耗了大量的—OH活性基团,导致其缺乏活性基团而无法键合到试样表面,降低了疏水性能.从图9中分析得到,每100mL硅氧烷溶液中水的含量在3-5mol的区间内,硅氧烷既可以在老化过程中充分水解,又不影响硅氧烷在自组装过程中的扩散和与表面的键合,得到的膜层疏水性能最佳.2.2.3自组装时间对表面疏水性能的影响经阳极氧化后的试样浸入到G502溶液中,每100mL自组装溶液的含水量为3.7mol,自组装时间分别设置为10min及0.5、1、1.5、2、4、6、8、120h.水滴在表面的静态接触角与自组装时间关系曲线,如图10所示.自组装10min的试样,接触角几乎为0°.当自组装时间较短时(<1.5h),接触角随着自组装时间的增加而缓慢增大.认为水解后的硅氧烷只在试样表面很小的面积上发生键合,而没有完全覆盖试样表面.根据硅氧烷在—OH活性表面的生长动力学,其首先在表面形成较小的岛状聚硅氧烷,覆盖图9水滴在试样表面的静态接触角与G502溶液(100mL0.01mol·L-1)中的含水量关系曲线Fig.9Relation curve of static contact angles of water droplets on the surfaces and the quantities of water in 100mL0.01mol·L-1G502solution图10水滴在试样表面的静态接触角与自组装时间的关系曲线Fig.10Relationship curve of static contact angles of water droplets on the surfaces and immersion time图8G502与试样表面键合示意图Fig.8Scheme graph of the surface bonding betweenG502and the sample2587Acta Phys.-Chim.Sin.,2009Vol.25率很小,随着时间的延长,岛状聚硅氧烷的生长增大了覆盖率,表现为疏水性的提高[38,39].在自组装1.5-2h的区间内,接触角急剧增大,表面由亲水性转变为疏水性,这是由于在这一区间内出现了完全覆盖的临界值,越过这一临界值,接触角即迅速增大.当自组装时间为4h,θS=157.5°±2.0°,表面呈超疏水性.当自组装时间大于4h所制备的表面与水的静态接触角缓慢下降.另外,当自组装时间延长至120h时,θS=103.6°±5.5°,与水滴在平滑聚硅氧烷表面的接触角(110.2°±1.0°)相近,可能是由于硅氧烷在表面长时间均匀生长,填补了表面微米级的起伏,使表面趋于平滑,失去了构成三相界面的孔隙,导致表面呈弱疏水性.由以上分析可以看出,经阳极氧化后的试样浸入到硅氧烷溶液中自组装4h得到的表面疏水性能最佳.2.3耐蚀性能测试利用动电位极化的方法对比了经工艺优化后制备的超疏水膜层、阳极氧化后的铝合金试样和经前处理后的铝合金试样的耐电化学腐蚀性能.其中,制备阳极氧化铝合金试样所采用的阳极氧化电流密度为2.25A·dm-2,制备超疏水膜层试样所采用的工艺参数为阳极氧化电流密度2.25A·dm-2,每100mL自组装溶液含水量为3-5mol,自组装时间为4h.图11为超疏水膜层、阳极氧化铝合金以及经前处理后的铝合金的动电位极化曲线.由图11以及试样的自腐蚀电位(Ecorr)和通过Tafel直线外推法计算得到的腐蚀电流密度(icorr)(见表3)可以得到,超疏水膜层Ecorr 为-0.53V,而只经前处理后的铝合金Ecorr为-0.75V,超疏水膜层Ecorr正移大于0.2V;同时,表面为超疏水膜层的铝合金与只经前处理后的铝合金相比,icorr下降了约2-3个数量级.Ecorr和icorr的结果表明,超疏水膜层的极化曲线的阳极分支和阴极分支都向电位正的方向移动,且腐蚀电流也保持在一个很低的数值(5.6×10-9A·cm-2),有效地提高了铝合金基体的耐蚀性.只经阳极氧化处理而表面未自组装硅氧烷的铝合金Ecorr为-0.64V,与只经前处理后的铝合金(-0.75V)和超疏水膜层(-0.53V)相比,说明铝合金表面原位生长的阳极氧化膜不仅为构造超疏水性能提供了粗糙结构,而且在一定程度上提高了铝合金的耐蚀性.这是由于在NaCl水溶液中阳极氧化膜层虽然起到了一定阻挡层的作用,但Cl-易渗入多孔的氧化铝膜中,限制了氧化膜层的耐蚀作用[40],而在原位生长的阳极氧化膜上自组装的超疏水膜层有效地防止了溶液中Cl-的渗入,极大地提高了铝合金的耐蚀性.另外,由图10中三种试样极化曲线的阴极极化区的形状及电流密度可以看出,只经前处理和经阳极氧化的铝合金试样几乎一致,而超疏水膜层阴极极化区电流密度非常小,说明在阴极极化区超疏水膜层很好地保护了铝合金基体.3结论(1)讨论了阳极氧化电流密度和自组装溶液中水的含量及自组装时间对表面疏水性的影响,并得到了制备超疏水表面的最佳工艺参数,即阳极氧化电流密度为2.25A·dm-2,每100mL自组装溶液含水量为3-5mol,自组装时间为4h.(2)通过阳极氧化在铝合金表面原位构造微米尺度的粗糙结构,协同表面自组装低表面能的聚硅氧烷膜层制备了静态接触角θS=157.5°±2.0°,且接触角滞后小于3°的超疏水自清洁表面.(3)FE-SEM及AFM测试结果表明,由自组装表3经前处理后的铝合金、阳极氧化后的铝合金和铝合金表面超疏水膜层在3.5%(w)NaCl水溶液中的自腐蚀电位及腐蚀电流密度Table3Corrosion potential(E corr)and corrosioncurrent density(i corr)of pre-treated aluminum alloy,anodized aluminum alloy and super-hydrophobic filmon aluminum alloy in3.5%(w)NaCl aqueous solutions图11经前处理后的铝合金(a)、阳极氧化后的铝合金(b)和铝合金表面超疏水膜层(c)在3.5%(w)NaCl水溶液中的动电位极化曲线Fig.11Potentiodynamic polarization curves of pre-treated aluminum alloy(a),anodized aluminum alloy (b)and super-hydrophobic film on aluminum alloy(c)in3.5%(w)NaCl aqueous solutionsSample E corr/mV(vs SCE)i corr/(A·cm-2) pre-treated aluminum alloy-0.75 2.1×10-6 anodized aluminum alloy-0.64 1.0×10-6 super-hydrophobic film-0.53 5.6×10-92588。

聚乙烯基咪唑

Controlled Radical Polymerization of4-VinylimidazoleMichael H.Allen,Jr.,Sean T.Hemp,Adam E.Smith,and Timothy E.Long*Department of Chemistry,Macromolecules and Interfaces Institute,Virginia Tech,Blacksburg,Virginia24061,United States *Supporting Informationweight growth to number-average molecular weights(M n)of65addition conﬁrmed the presence of the trithiocarbonate functionality atpolymerization conditions.Polymerizations in traditional aqueouscontrolled molecular weight growth.Eﬀectively controlling4VIMcopolymers for emerging applications including nucleic acidMany researchers currently focus on the incorporation of the imidazole ring into a variety of macromolecules for biological and engineering applications.1−4The imidazole ring,which is found in the amino acid histidine,displays good biocompat-ibility and the capacity to condense and deliver DNA.5,6 Additionally,quantitative alkylation imparts a permanent, cationic charge on the imidazole ring.These imidazolium salts,commonly referred to as ionic liquids,exhibit high ionic conductivities,high chemical and thermal stability,and negligible volatility.7−10Imidazole-containing ionic liquid monomers include(meth)acrylics,11−13styrenics,14−17and1-, 2-,and4-vinylimidazoles(1VIM,2VIM,and4VIM).18−32 Conventional free radical polymerization of these ionic liquid monomers enables ionically conductiveﬁlms,33,34microwave-absorbing materials,35and CO2-capturing membranes.36,37 Although conventional free radical polymerization results in numerous polymerized ionic liquids,controlled radical polymerization(CRP)further enables the design of macro-molecules with well-deﬁned architectures and precise molecular weights.38,39Attempts to polymerize imidazole-containing monomers in a controlled fashion include atom transfer radical polymerization(ATRP),nitroxide-mediated polymerization (NMP),and reversible addition−fragmentation chain transfer (RAFT).Shen et al.polymerized2-(1-butylimidazolium-3-yl)ethyl methacrylate tetraﬂuoroborate(BIMT)with ATRP with a Cu(I)Cl catalyst to control molecular weight.40Gnanou et al.homopolymerized BIMT employing RAFT polymer-ization and synthesized doubly hydrophilic block copolymers of BIMT with methacrylic acid.41Researchers also used NMP for styrenic-based imidazolium polymers of controlled architecture and well-deﬁned molecular weights for CO2absorption membranes,poly(ionic liquid)brush coatings for surfaces, and micelle self-assembly.16,17,42Moreover,Mahanthappa and co-workers recently studied the thermal,ion transport,and morphological properties of these charged homopolymers.14,15 N-Vinyl radicals such as1VIM form a highly reactive, unstable,propagating radical due to the absence of resonance stabilization,and the CRP of1VIM proved diﬃcult until only recently.Liu et al.utilized RAFT polymerization with a xanthate chain transfer agent(CTA)to synthesize poly(N-isopropylacrylamide-b-1VIM)block copolymers.43Thereafter, xanthate CTAs successfully mediated polymerization of three N-vinylimidazolium salts in a controlled fashion.44The polymerized ionic liquids,however,displayed broad poly-dispersities(PDIs),and experimental molecular weights deviated from theoretical predictions.Cobalt-mediated con-trolled radical polymerization of1-vinyl-3-ethylimidazolium bromide demonstrated improved polymer molecular weight control with narrow PDIs.45Despite increased resonance stabilization of the propagating radical relative to1VIM,CRP of4VIM remains unexplored. Overberger and co-workersﬁrst polymerized4VIM using conventional free radical polymerization in benzene.27TheyReceived:March16,2012Revised:April15,2012Published:April25,2012synthesized copolymers to examine the esterolytic activity of various imidazole-containing macromolecules.20−26,28Breslow et al.subsequently synthesized poly(4VIM)according to Overberger’s methods to ascertain the catalytic eﬀects on the reaction between pyridoxamines and pyruvic acid.Furthermore, they attempted RAFT polymerization of4VIM to produce polymers with narrow PDIs;however,the polymerizations generated gels without molecular weight control.46In addition to catalysis studies,poly(4VIM)also displays potential as an eﬀective nonviral gene transfection with minimal cytotox-icity.47,48Bozkurt and co-workers prepared4VIM copolymers with acidic comonomers(vinylphosphonic acid,4-vinyl-benzylboronic acid)to generate anhydrous proton conducting membranes for methanol fuel cells.49−52RAFT polymerization permits controlled polymerization of a variety of functional monomers including less stable O-and N-vinyl radicals.39,53,54RAFT imparts control of polymerizations through a series of reversible chain transfer reactions,which minimizes the instantaneous concentration of radicals, consequently reducing bimolecular termination.55An assort-ment of thiocarbonylthio compounds serve as CTAs including dithioesters,xanthates,dithiocarbamates,and trithiocarbonates to mediate and control RAFT polymerizations.Through CTA and solvent selection,initiator and monomer concentrations, and diﬀerent target molecular weights,RAFT provides numerous avenues to control the polymerization of functionally rich monomers.53In this article,we demonstrate the unprecedented CRP of 4V I M.A t r i t h i o c a r b o n a t e,4-c y a n o-4-(ethylsulfanylthiocarbonylsulfanyl)pentanoic acid(CEP),suc-cessfully mediated the controlled polymerization of4VIM.We varied multiple reaction parameters including solvent,initiator concentration,monomer concentration,and target molecular weight to examine the eﬃcacy of RAFT polymerization of 4VIM.Glacial acetic acid,which served as a unique solvent, maintained a homogeneous polymerization and allowed the synthesis of poly(4VIM)with controlled molecular weights and narrow PDIs.Successful chain extension experiments further demonstrated the integrity of the thiocarbonylthio end groups and the controlled nature of these polymerizations.RAFT polymerization of4VIM enables the future design of block copolymers for advanced applications including pH-sensitive block copolymers for gene delivery and ionically conductiveblock copolymers for electroactive devices.■EXPERIMENTAL SECTIONMaterials.Urocanic acid(Aldrich,99%)was recrystallized from water and dried under reduced pressure for18h.1VIM was distilled at 1mmHg and60°C(Aldrich,99%).2,2′-Azobis(isobutyronitrile) (AIBN,Aldrich,99%)and4,4-azobis(4-cyanovaleric acid)(V-501, Aldrich,98%)were recrystallized from methanol.CEP56and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)nitroxide(SG1)57 were synthesized according to literature procedures.Glacial acetic acid (Alfa Aesar,99.7%),methanol(Fisher Scientiﬁc,HPLC grade), DMSO(Fisher Scientiﬁc,HPLC grade),and Blocbuilder(Arkema Inc.)were used as received.Analytical Techniques.1H NMR spectroscopy(Varian Inova, 400MHz,CD3OD,d6-DMSO)conﬁrmed monomer and polymer structures and determined monomer conversion.Diﬀerential scanning calorimetry(TA Instruments,Q1000)determined thermal transitions. The molecular weight of the polymers was measured using aqueous size exclusion chromatography(SEC)(ﬂow rate of0.8mL/min through two Waters Ultrahydrogel Linear and one Waters Ultra-hydrogel250columns,solvent:54/23/23H2O/MeOH/acetic acid (v/v/v%),0.1M NaNO3).SEC instrumentation included a Waters 1515isocratic HPLC pump,a Waters717plus autosampler,a Wyatt miniDAWN multiangle laser light scattering(MALLS)detector operating at a wavelength of690nm,and a Waters2414diﬀerential refractive index detector.The speciﬁc refractive index increment values (d n/d c)were determined oﬄine using a Wyatt Optilab T-rEX refractive index detector at658nm and35°C to obtain absolute polymer molecular weights using SEC.The d n/d c values for linear poly(1VIM)and poly(4VIM)were0.2212±0.0004and0.2296±0.0008mL/g,respectively.Absolute polymer molecular weights and PDIs were calculated using the Wyatt ASTRA SEC/LS software and compared to theoretical predictions.Dynamic light scattering with a Malvern Zetasizer NanoZS conﬁrmed that the aqueous mobile phase prevented formation of large scale polymer aggregates.Synthesis of4VIM.4VIM was prepared according to a modiﬁed literature procedure.27Anhydrous urocanic acid(5.00g,53.0mmol) was heated under vacuum(1mmHg)at220−240°C to melt and decarboxylate the compound(Supporting Information,Scheme S1). After continuous heating,the product distilled as a colorless liquid that crystallized readily at23°C.The oﬀ-white powder sublimed at80°C under vacuum(0.5mmHg)to further purify the4VIM.White crystals (1.70g,53%yield)were collected on the coldﬁnger and were dried under reduced pressure.1H NMR(400MHz,d6-DMSO):δ12.11(s, 1H),7.59(s,1H),7.04(s,1H),6.55(dd,1H),5.58(dd,1H),4.98(m, 1H).Conventional Free Radical Homopolymerization of1VIM and4VIM.In a25mL,round-bottomedﬂask equipped with a stir bar, each monomer(2.00g,21.3mmol)was charged with0.1mol%AIBN (3.49mg,2.13×10−2mmol)and dissolved in glacial acetic acid(8.00 g,133mmol).The reaction was sparged with argon at room temperature for30min and placed in an oil bath at65°C for24h. The reaction remained homogeneous and was precipitated into acetone,redissolved in methanol,and precipitated a second time into acetone.The polymer was dried18h under reduced pressure(1.80g, 90%yield).Absolute polymer molecular weights were determined using aqueous SEC.Typical M n values were5.00×104and1.10×106 g/mol with PDIs of1.52and1.54for poly(1VIM)and poly(4VIM), respectively.NMP of4VIM.In a representative NMP,4VIM(0.600g,6.38 mmol),Blocbuilder(2.43mg,6.37μmol),SG1(0.38mg,1.28μmol), and glacial acetic acid(6.69g,111mmol)were added to a25mL, round-bottomedﬂask equipped with a stir bar.The reaction was sparged with argon for30min,and the reaction was subsequently immersed in an oil bath maintained at110°C.Aliquots were removed during the course of the reaction to obtain kinetics of the polymerization.RAFT Polymerization of4VIM.In a representative RAFT polymerization,4VIM(0.250g,2.66mmol),V-501(2.98mg,10.6μmol),CEP(2.80mg,10.6μmol),and glacial acetic acid(2.79g,46.5 mmol)were added to a25mL,round-bottomedﬂask equipped with a stir bar.The reaction was sparged with argon for30min,and the reaction was subsequently immersed in an oil bath thermostated at70°C.Samples were withdrawn during the course of the polymerization with an argon-ﬂushed syringe to monitor monomer consumption and polymer molecular weight increase as a function of reaction time. Monomer conversion was determined with1H NMR spectroscopy in CD3OD.Aqueous SEC provided molecular weight data for the polymerization aliquots.■RESULTS AND DISCUSSIONThree CRP techniques are commonly employed to produce functional polymers with tailored compositions and architec-tures,including ATRP,NMP,and RAFT.Heterogeneous polymerizations are also eﬀective to control molecular weight, including dispersion,suspension,emulsion,and miniemulsion polymerizations;however,these techniques involve added surfactants and other stabilizers to intentionally create a two-phase system.58Performing CRP in solution without additives, surfactants,and emulsiﬁers typically requires a good solvent toensure homogeneous conditions.These conditions prevent the occurrence of uncontrolled molecular weight growth and broad PDIs.Numerous earlier studies performed conventional free radical polymerization of4VIM in benzene;however,the polymerization was heterogeneous as the polymer precipitated during the process.20−28,48Ihm et al.reported a weight-average molecular weight(M w)of26200g/mol under these conditions (0.1mol%AIBN,PDI not reported),which remains the only report of molecular weight data for a4VIM homopolymer in the literature.48It was necessary to identify a new solvent for 4VIM homopolymerizations to overcome these earlier heterogeneous reaction conditions.Dissolution of4VIM and its subsequent homopolymer proved diﬃcult due to intermolecular hydrogen bonding,which prevented homogeneous polymerizations in organic(DMSO, DMF)and aqueous mixtures for the polymerization of1VIM.21 The conventional free radical polymerizations of1VIM and4VIM in glacial acetic acid aﬀorded homopolymers under homogeneous reaction conditions as shown in Scheme1a.Subsequent dialysis enables the recovery of the unprotonated poly(4VIM),which dissolves readily in methanol and DMSO. In addition,Scheme1b depicts the resonance contributors of the propagating radical for each monomer to illustrate4VIMs increased radical stability relative to1VIM.Aqueous size exclusion chromatography determined the absolute molecular weight(M n poly(4VIM)=1.10×106g/mol;M n poly(1VIM) =5.00×104g/mol)of each polymer as shown in Figure1.A higher k t/k p ratio for1VIM relative to the more stable 4VIM propagating radical presumably accounted for the signiﬁcant diﬀerence in polymer molecular weights.Moreover, comparing the experimentally obtained poly(4VIM)molecular weight(M w=1.69×106g/mol)to previous literature(M w= 2.26×104g/mol)suggested the homogeneous polymerization conditions improved the range of attainable molecular weights. Diﬀerential scanning calorimetry determined the glass tran-sition temperatures(T g)of each polymer(T g poly(1VIM)= 175°C;T g poly(4VIM)=218°C),and the increased T g of poly(4VIM)was attributed to the presence of both a hydrogen bond donor and acceptor,leading to signiﬁcant intra-and intermolecular hydrogen bonding.The increased radical stability of the4VIM propagating radical and the development of homogeneous polymerization conditions spurred our investigation of CRP in glacial acetic acid.For the polymerization of imidazole-containing mono-mers,ATRP remained problematic due to catalyst complex-ation;59therefore,we investigated the CRP of4VIM utilizing NMP and RAFT polymerization strategies.NMP of4VIM (Scheme2)proved problematic as various SG1and monomerconcentrations resulted in less than10%monomer conversion with higher molecular weights than theoretical predictions. The degradation of SG1under acidic conditions contributed to this lack of control.60In addition,homogeneous polymer-izations in DMSO at110°C also remained uncontrolled.We attributed the absence of control to the decreased4VIM propagating radical stability relative to monomers traditionally polymerized using NMP(acrylates and styrenics).NMP of 1VIM under similar conditions failed to produce polymer, which was also ascribed to decreased radical stability. Because of the limitations of NMP to polymerize a variety of functional monomers,we probed the RAFT polymerization of 4VIM.Recently,numerous studies demonstrated the impor-tance of fundamentally understanding RAFT polymerization kinetics of previously uncontrolled monomers.44,61−63These studies have accelerated the discovery of novel structures for many critical technologies.Careful selection of the CTA and polymerization reaction conditions remains a critical decision in performing successful RAFT polymerizations.53Numerous amine-containing monomers with RAFT polymerization conditions required an acidic buﬀer to prevent CTA aminolysis.64Thang et al.demonstrated that trithiocarbonate CTAs exhibited increased hydrolytic stability compared to the corresponding dithioesters.65In addition,Moad and Mc-Cormick discovered that trithiocarbonate CTAs eﬀectively controlled more reactive monomers such as acrylamides and methacrylamides.55,66Endo et al.polymerized N-vinylimidazo-lium salts using xanthate-based CTAs;however,the more activeScheme1.(a)Conventional Free Radical Homopolymerization of Poly(4VIM)and Poly(1VIM)in Glacial Acetic Acid;(b)Resonance Structures of the Respective PropagatingRadical Figure 1.Aqueous SEC light scattering chromatograms of poly-(4VIM)(M n=1100000g/mol,PDI=1.54)and poly(1VIM)(M n= 50000g/mol,PDI=1.52).Scheme2.NMP of4VIM with Blocbuilder andSG1xanthate CTAs proved unnecessary with the increased radical stability of 4VIM.44As shown in Scheme 3,the RAFT polymerization of 4VIMoccurred in an acetate bu ﬀer (pH =5.2)with CEP as the CTA.The reaction conditions targeted an M n of 23500g/mol at 100%conversion;however,as the reaction time increased,the polymer molecular weights exceeded target molecular weight and exhibited broad PDIs (>1.60)(Table 1).The uncontrolled molecular weight growth suggested that 4VIM remained partially unprotonated,contributing to CTA aminolysis during polymerization (Figure S1).To increase the acidity of the solution and ensure complete protonation of 4VIM,we performed RAFT polymerizations in glacial acetic acid (Scheme 4).Initial experiments demonstrated the absence of CTA aminolysis under these conditions.The in ﬂuence of initiator concentration,monomer concentration,and targeted molecular weight on the polymerization were studied to probe the feasibility of RAFT polymerization in this unconventional solvent.Initial reaction conditions revealed the in ﬂuence of increasing the initiator concentration (V-501)while maintaining a 250/1[4VIM]/[CEP]molar ratio.Aqueous SEC-MALLS showed a shift in molecular weight distribution to shorter elution times as the 4VIM RAFT homopolymerization progressed (Figure 2a,[CEP]/[V-501]=2).The unimodal SEC traces combined with the systematic shift in elution time indicated an absence of high molecular weight termination products and uncontrolled homopolymerization.Figure 2b shows the expected increase in the apparent polymerization rate as the initiator concen-tration increased.Scheme 3.Aqueous RAFT Polymerization of Poly(4-vinylimidazole)in 1M Acetate Bu ﬀerTable 1.Molecular Weight Analysis of 4VIM RAFT Homopolymerization in 1M Acetate Bu ﬀer (pH =5.2)atime (min)M n b (g/mol)PDI time (min)M n b (g/mol)PDI301800 1.1012035000 1.74605100 1.6118062200 1.679020200 1.7124070900 1.61a [4VIM]/[CEP]/[V-501]=500:2:1,[4VIM]=0.250M.b Absolute molecular weights determined with aqueous SEC-MALLS.Scheme 4.RAFT Polymerization of 4VIM at 70°C in Glacial AceticAcidFigure 2.(a)Representative aqueous SEC light scattering chromato-grams displaying the increase in polymer molecular weight as RAFT polymerization progressed.(b)Pseudo-ﬁrst-order kinetics plot for the RAFT polymerization of 4VIM (0.25M)in glacial acetic acid at 70°Cemploying various [CEP]/[V-501]concentrationswhile maintaining atarget DP of 250.(c)Dependence of M n and PDI on monomerconversion utilizing various [CEP]/[V-501]concentrations.McCormick and co-workers ascribed the increasing slopes with increasing initiator concentration to the participation of more propagating chains during RAFT polymerization.67We examined various [CEP]/[V-501]molar ratios from 4to 1;however,a [CEP]/[V-501]=4ratio exhibited inappreciable conversion over the 8h experiment.The [CEP]/[V-501]=2molar ratio displayed an induction period of 45min while a [CEP]/[V-501]=1molar ratio did not have an induction period.Literature suggests that induction periods occur when R •(from CTA)reinitiates slowly or preferentially combines with the CTA.68Increasing the number of radicals at the beginning of the reaction typically reduces or eliminates the inhibition period.The pseudo-ﬁrst-order kinetic plots for the di ﬀerent initiator concentrations remained linear for ∼4h where a change in slope occurred.The linear portion of the kinetic plot prior to the change in slope at 4h established the apparent rate constants,k app ,for each polymerization (entries A and B in Table 2).The RAFT polymerization of acrylamides and methacryla-mides typically display a similar change in slope attributed to a reduction in radicals in the main RAFT equilibrium or a change in the propagation rate constant.53,67,69Figure 2c further demonstrates excellent molecular weight control,depicting linear increases in molecular weight with increasing conversion while maintaining narrow PDIs (<1.20)up to 80%conversion.The overlap of experimental molecular weights with theoretical predictions also indicates a well-controlled polymerization.In addition to varying the [CEP]/[V-501]molar ratio,we also studied the impact of 4VIM monomer concentration on the RAFT polymerization kinetics.The increased monomer concentration (0.25to 0.50M)resulted in faster kinetics as expected (Figure 3a;entries A and C in Table 2).The linearity of the plots indicated pseudo-ﬁrst-order behavior.Likewise,a change in slope occurred for reaction times above 3h,as discussed previously.The polymerizations proceeded to quantitative conversions with PDIs <1.20.Figure 3b demonstrates good agreement between experimental and theoretical molecular weights.The adjustment of the [4VIM]/[CEP]molar ratio while maintaining a constant [CEP]/[V-501]=2molar ratio targeted higher degrees of polymerization.Figure 4a shows linear pseudo-ﬁrst-order kinetics regardless of targeted degree of polymerization.As the target molecular weight increased,the reaction rates decreased signi ﬁcantly due to a reduction in the concentration of active propagating chains as explained previously (entries A,D,and E in Table 2).The linear evolution of experimental molecular weights versus conversion occurred at all polymer-ization conditions with narrow PDIs as revealed in Figure 4b,c.The experimental molecular weights displayed good agreementwith theoretical predictions,producing well-de ﬁned 4VIMhomopolymers to 33000g/mol with PDIs as low as 1.06.Upon identi ﬁcation of optimized reaction conditions forcontrolled RAFT polymerization of 4VIM,reaction conditions were identi ﬁed to produce polymers with M n ’s exceeding 30000g/mol (Figure S2).The reactions ([4VIM]/[CEP]/[V-501]=2000/2/1or 1000/1/1,1.0M,17h)produced higher molecular weight polymers (M n =51000and 65000g/mol;PDI =1.04and 1.02,respectively).These results con ﬁrmed that RAFT polymerization in glacial acetic acid producedprecise 4VIM homopolymers under various conditions with a broad range of molecular weights with narrow PDIs (M n =1000−65000g/mol;PDIs =1.02−1.19).In sharp contrast,theRAFT polymerization of 1VIM failed to produce any polymer under similar conditions.The synthesis of a 4VIM macroCTA and subsequent monomer addition with additional 4VIM produced a “diblock ”copolymer,further demonstrating the controlled RAFT polymerization of 4VIM.The polymerization employed identical reaction conditions as discussed previously in Figure 2a utilizing a [CEP]/[V-501]=2.Figure 5shows an SEC chromatogram of the macroCTA (M n =16900g/mol;PDI =1.02)with a clear shift in elution time when chain-extendedwith additional 4VIM.Table 2.Apparent Rate Constants (k app )for the RAFT Polymerization of 4VIM under Various Reaction Conditions entry [CTA]/[I][4VIM](M)M n at 100%conv k app (s −1)A 20.25023500(DP =250) 5.0×10−5B 10.25023500(DP =250)9.2×10−5C 20.50023500(DP =250) 1.2×10−4D 20.50047000(DP =500) 2.5×10−5E 20.50094100(DP =1000)0.7×10−5Figure 3.(a)Pseudo-ﬁrst-order kinetics plot for the RAFT polymerization of 4VIM in glacial acetic acid at 70°C with various monomerconcentrations ([CEP]/[V-501]=2;[4VIM]/[CEP]=250).(b)Dependence of M n and PDI on monomer conversion at di ﬀerent reaction solution concentrations.The chain extension produced a “diblock ”copolymer with an M n =37300g/mol and PDI =1.04.The narrow PDI and absence of a high molecular weight shoulder suggested the macroCTA retained the trithiocarbonate functionality at the chain end.The lack of termination products demonstrated further proof of e ﬀective polymerization control.■CONCLUSIONS The RAFT polymerization of 4VIM in glacial acetic acid produced well-de ﬁned,monodisperse homopolymers.We demonstrated,for the ﬁrst time to our knowledge,the CRP of 4VIM.RAFT polymerization of 4VIMcreated macro-molecules with an M n ≤65000g/mol with PDIs below 1.20.We revealed through the variation of numerous reaction conditions that the RAFT polymerization of 4VIM remained controlled;however,NMP failed to control 4VIM homo-polymerization.Aqueous SEC showed monomodal peaks with clear shifts in elution times as monomer conversion increased.The experimental absolute molecular weights displayed excellent agreement with theoretical predictions.All reactions displayed linear,pseudo-ﬁrst-order kinetics.Chain extension experiments suggested the preservation of the trithiocarbonate functionality at the chain ends.The use of traditional aqueous RAFT solvents (acetate bu ﬀer)for amine-containing mono-mers exhibited uncontrolled molecular weight growth lending to the importance of glacial acetic acid as the reaction solvent.We plan to investigate the polymerization of 4VIM with additional comonomers using RAFT polymerization.CRP of 4VIM will enable the development of imidazole-containing block copolymers for various applications including nonviral gene delivery and electroactive device fabrication.■ASSOCIATED CONTENT*Supporting Information 1H NMR,DSC,and SEC characterization of homopolymers.This material is available free of charge via the Internet at.■AUTHOR INFORMATION Corresponding Author *E-mail:telong@.NotesThe authors declare no competing ﬁnancial interest.■ACKNOWLEDGMENTSThe authors acknowledge Arkema,Inc.,for their generous donation of Blocbuilder for controlled radical polymerization studies.This material is based upon work supported in part by the Macromolecular Interfaces with Life Sciences (MILES)Integrative Graduate Education and Research Traineeship(IGERT)of the National Science Foundation under Agree-ment DGE-0333378.This material is also based upon work supported in part by the US Army Research O ﬃce under Grant W911NF-07-1-0452Ionic Liquids in Electro-ActiveDevicesFigure 4.(a)Pseudo-ﬁrst-order kinetics plot for the RAFT polymerization of 4VIM in glacial acetic acid ([4VIM]=0.50M;[CEP]/[V-501]=2)at 70°C employing various [4VIM]/[CEP]concentrations.(b)Dependenceof M n on monomerconversion utilizing various [4VIM]/[CEP]concentrations.(c)Dependence of PDI on monomer conversion utilizing various [4VIM]/[CEP]concentrations.Figure 5.Aqueous SEC light scattering traces for the 4VIM macroCTA (M n =16900g/mol,PDI =1.02)and the correspondingchain extended “block ”copolymer (M n =37300g/mol,PDI =1.04).(ILEAD)MURI.This material is based on work partially supported by the U.S.Army Research Laboratory and the U.S. Army Research Oﬃce under the Army Materials Center of Excellence Program,Contract 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双重敏感mPEG-PDPA-P(AAm-co-AN)_聚合物自组装体的药物递送

功能高分子学报Vol. 36 No. 1 58Journal of Functional Polymers2023 年 2 月文章编号： 1008-9357(2023)01-0058-11DOI: 10.14133/ki.1008-9357.20220322001双重敏感mPEG-PDPA-P(AAm-co-AN)聚合物自组装体的药物递送宋佳，张紫薇，张婕，秦飞扬，徐首红（华东理工大学化学与分子工程学院, 结构可控先进功能材料及其制备教育部重点实验室, 上海 200237）摘要：设计合成了一种新型两亲性三嵌段ABC聚合物聚乙二醇单甲醚-聚甲基丙烯酸二异丙胺基乙酯-聚(丙烯酰胺-co-丙烯腈)(mPEG-PDPA-P(AAm-co-AN))。

该聚合物具有pH敏感嵌段PDPA和温度敏感嵌段P(AAm-co-AN)，临界溶解温度(UCST)较高，且可以通过改变单体比例来调节UCST。

在室温、中性环境下，该聚合物通过自组装形成刺激响应型胶束，可用于抗肿瘤药物的控释研究。

温度升高诱导聚合物胶束向不对称囊泡结构转变，pH降低促使聚合物形成更加松散的胶束。

在体外释药探究中，聚合物胶束对亲水药物阿霉素(DOX)和疏水药物槲皮素都具有良好的载药效果，在37 ℃、pH=7.4的条件下泄漏量低，随着温度升高和pH降低，胶束释放药物的速率和释放量明显增加。

关键词：三嵌段聚合物；聚合物胶束；温度/pH双重响应；药物控释；自组装；药物递送中图分类号： O648.2 文献标志码： ASelf-Assembly of Dual-Sensitive mPEG-PDPA-P(AAm-co-AN) forDrug DeliverySONG Jia, ZHANG Ziwei, ZHANG Jie, QIN Feiyang, XU Shouhong（Key Laboratory for Advanced Materials, School of Chemistry and Molecular Engineering, East China University ofScience and Technology, Shanghai 200237, China）Abstract:Poly(ethylene glycol) monomethyl ether-poly(2-diisopropylaminoethyl methacry-late)-poly(acrylamide-co-acrylonitrile) (mPEG-PDPA-P(AAm-co-AN)), a novel amphiphilic triblock ABC polymer, was designed and synthesized. This polymer was prepared by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT). When pH changes, PDPA undergoes a hydrophilic-hydrophobic transition. Therefore, the polymer has pH-responsivity with a pH-sensitive point at pH 6.53. The P(AAm-co-AN) fragment forms hydrogen bonds at low temperature. At high temperature, hydrogen bonds are formed between the polymer chains and water molecules so that the polymer mPEG-PDPA-P(AAm-co-AN) has a high critical solution temperature (UCST). By varying the monomer ratios of acrylamide (AAm) to acrylonitrile (AN) and the concentration of the solution, polymers with different UCSTs can be收稿日期： 2022-03-22基金项目：国家自然科学基金(22078087)作者简介：宋　佳（1997—），女，硕士生，主要研究方向为智能药物载体设计与合成。

金属有机框架(MOFs)在锂和钠离子电池中的应用

金属有机框架(MOFS)在锂和钠离子电池中的应用金属有机框架金属有机框架(metal-organic frameworks, Me)FS)由YAGHI 和Ll 在20世纪90年代末首次提出，主要由金属离子和有机连接物组成，金属离子可以是过渡金属、碱土金属或偶系元素的离子，有机连接物通常是带有N或多齿原子(毗咤基、多胺、竣酸盐等)的多齿分子。

MOFs因为其轻质(~0.13g/Cm3)、高比表面积(IOOOOm2/g)、结构和组成多样的特点而受到广泛关注，在气体存储或分离、催化、药物输送和成像等领域有着广泛的应用前景。

越来越多的研究显示MOFs 材料具有的复杂体系结构和独特化学成分可用于电化学储能和转换, 实现在二次电池、超级电容器和燃料电池等领域的应用，而可控合成的MOFs及其衍生纳米材料为研究和调整其应用提供了可能，图1和表1总结了各种制备MOFs 及其衍生纳米材料的方法和特点。

图1 MOFs前驱体及其衍生纳米材料的合成策略综述表1 MOFs前驱体合成方法综述Methods Typical examples FeaturesControlled etchingZIF-67 frames1111 NjCoPBAcagcJy Gcnerationofhollw structures Retention of oπgιnal MOF structuresOutward dιflusιon Ni/Zn-MOF-2 boxcs,π, Fc-MOF-5cages,141Generation Ofhol low structures Retention of oπgιnalMOF structuresImpregnation WIth functional speαcs PtZMIL-IOI1151AUNI/MIL-IOIUSSimple method to produce MOF composites Hard totune the incorporated nanospeciesBlending assembly Aι√ZIF-8 PamCIe3TiO√ZIF-67 PanIdeS ㈣Easy to ιn∞rpcrate diflerent nanospecies Limitation inMOF hostsSurfaceZintcrfiice growth Te@ZIF-8 nanowιres,l,∙ Fc-soc-MOF colloιdosomcs l141Formation of MOF shells on substrate matenaJsGeneration ofMOF compositesSurface ∞atιng with functional shells UK‰66"iθ2particlcsMZr-CP∕SιO r PE<; PartICkS川Formation of functional shells on MOFs GenaaUOn ofMOF compositesElcctraspinning ZIF-8∕PS fibers1221General synthesis of MOF/polymcr fibersMOFS衍生金属氧化物在所有已报道的锂和钠离子电池负极材料中，金属氧化物因高能量密度(600~1500mA ∙ h∕g)和经济环保的优势成为下一代负极材料的候选之一。

超分子化学光催化体系

here is focused only on the supramolecular chemistry necessary to create a formable catalytic material and therefore does not explore its possible integration into a photocathode that would not require a sacriﬁcial electron donor. We designed a charged amphiphilic chromophore with the capacity to self-assemble into supramolecular polymers via hydrophobic collapse. At sufﬁciently high concentrations and under electrostatic screening conditions, charged supramolecular polymers can easily produce a threedimensional (3D) network that takes the form of a gel. These networks could be highly hydrated and host the soluble components necessary to produce the solar fuel. At the same time, much like natural photosynthetic antennae, supramolecular structures of conjugated molecules formed through π-orbital overlap should have the capacity to absorb light, split excitons and transport the charges to catalytic reaction centres. Despite the large body of work on the gelation and light-harvesting abilities of conjugated molecules14, the use of π-conjugated gels for artiﬁcial photosynthetic applications has not been reported. Through molecular design, we demonstrate here a supramolecular catalytic system that localizes catalysts within chromophore gels using electrostatic attraction.

北大考研-化学与分子工程学院研究生导师简介-严纯华

爱考机构-北大考研-化学与分子工程学院研究生导师简介-严纯华严纯华无机化学，博士，长江特聘教授电话：62754179传真：62754179电子信箱：yan@学士(1982)、硕士(1985)、博士(1988)，北京大学；讲师(1988-1989)、副教授(1989-1991)、教授(1991迄今)，北京大学化学院；英国皇家学会高级访问学者(1992)；日本学术振兴会访问教授(1993)；韩国科学技术研究院访问研究员(1996)；现任稀土材料化学及应用国家重点实验室主任、北京大学-香港大学稀土生物无机和材料化学联合实验室主任；主讲课程：研究生课程：现代化学进展、高等无机化学讨论研究组主要成员：副教授：廖春生、孙聆东、张亚文、王哲明博士后：苏慧兰、何成、高恩庆、徐刚、魏柳荷研究领域和兴趣：在稀土分离方法和理论研究的基础上，通过简单的化学制备方法，控制体系的结构和微结构、尺寸及其分布、形态和形貌，以及界面和表面，以期达到探索和提高稀土功能材料性质的目的。

具体研究领域为：(1)高纯稀土化合物分离及其工艺设计、控制；(2)功能稀土配合物的组装、结构与性质；(3)稀土复合氧化物纳米材料的制备与性质。

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聚氨酯及阻燃

耐热性、机械强度较高，而后者耐低温性能好，较柔软。几种基团的内聚能密度
c.
存在交联结构
赋予PU分子一些独特的性能，以及交联（交联剂）
和二级交联（氢键）。适度的交联可使聚氨酯材料的硬度、软化温度和弹性模量增加，断裂伸长率、永久变形和在溶剂中的溶胀度降低。
d . 耐热稳定性
耐热性次序为：脲 > 氨基甲酸酯 > 脲基甲酸酯 > 缩二脲
This simple procedure is then repeated to deposit a given number of cationic and anionic pairs, known as bilayers (BL). With LbL assembly, nanocoatings are conformally deposited directly onto a surface as a thin layer, which eliminates the challenges associated with processing or adversely modifying mechanical behavior when incorporating FR into the substrate itself
得应用。
聚氨酯在国内的发展
20世纪90年代至新世纪初，聚氨酯弹性体的适用范围进一步扩大，产品品种及产量稳步增长，原材料、新技术、先进设备正在协调配套生产成为
新世纪初的一个朝阳
产业。
聚氨酯的优异性能
与金属材料相比，聚氨酯制品具有重量轻、噪音低、耐损耗、加工费用低及耐腐蚀等优点；与塑料相比，聚氨酯弹性体具有不发脆、弹性记忆、耐磨等优点；
60%CH和40%PVS

石墨烯的功能化

© XXXX American Chemical Society
A B B C D G H I K M N N Q R R S S S S S T T T
A
1. INTRODUCTION Graphene, the two-dimensional sp2-hybridized carbon, is currently, without any doubt, the most intensively studied material. This single-atom-thick sheet of carbon atoms arrayed in a honeycomb pattern is the world’s thinnest, strongest, and stiﬀest material, as well as being an excellent conductor of both heat and electricity. It is no wonder that this two-dimensional material is considered, from the application viewpoint, to be even more promising than other nanostructured carbon allotropes, that is, 1-dimensional nanotubes and 0-dimensional fullerenes. Since the ﬁrst experimental evidence of the electronic properties of graphene in 2004,1 a major focus of experimental research has been concentrated on the development of new synthetic routes enabling an eﬀective production of well-deﬁned sheets.2−18 The commonly applied methods include the micromechanical1 or chemical exfoliation of graphite,13 chemical

【高分子专业英语翻译】

【高分子专业英语翻译】第五课乳液聚合大部分的乳液聚合都是由自由基引发的并且表现出其他自由基体系的很多特点,最主要的反应机理的不同源自小体积元中自由基增长的场所不同。

乳液聚合不仅允许在高反应速率下获得较高分子量,这在本体聚合中是无法实现或效率低下的,,同时还有其他重要的实用优点。

水吸收了大部分聚合热且有利于反应控制,产物在低粘度体系中获得,容易处理,可直接使用或是在凝聚,水洗,干燥之后很快转化成固体聚合物。

在共聚中,尽管共聚原理适用于乳液体系,单体在水相中溶解能力的不同也可能导致其与本体聚合行为不同,从而有重要的实际意义。

乳液聚合的变化很大,从包含单一单体,乳化剂,水和单一引发剂的简单体系到这些包含有2,3个单体,一次或分批添加,,混合乳化剂和助稳定剂以及包括链转移剂的复合引发体系。

单体和水相的比例允许变化范围很大,但是在技术做法上通常限制在30/70到60/40。

单体和水相比更高时则达到了直接聚合允许的极限,只有通过分批添加单体方法来排除聚合产生的大量的热。

更复杂的是随着胶体数的增加粘度也大大增加,尤其是当水溶性的单体和聚合物易容时,反应结束胶乳浓度降低。

这一阶段常常伴随着通过聚集作用或是在热力学不稳定时凝结作用而使胶粒尺寸增大。

第十课高分子的构型和构象本课中我们将使用根据经典有机化学术语而来的构型和构象这两个词。

构型异构是由于分子中存在一个或多个不对称中心,以最简单的C原子为例,每一碳原子的绝对构型为R型和S型,当存在双键时会有顺式和反式几何异构。

以合成聚合物为例,构型异构的典型问题和R.S型不对称碳原子在主链上的排布有关。

这些不对称碳原子要么来自不对称单体,如环氧丙烷,要么来自对称单体,如乙烯单体,,这些物质的聚合,在每个单体单元中形成至少一个不对称碳原子。

大分子中的构型异构源于侧链上存在不对称的碳原子,例如不对称乙烯单体的聚合,也是可能的,现今已经被广泛研究。

和经典有机化学术语一致,构象,旋转体,旋转异构体,构象异构体,指的是由于分子单键的内旋转而形成的空间排布的不同。

一例基于Keggin型多酸阴离子的双加帽杂多铌酸盐的合成、结构及表征

一例基于Keggin型多酸阴离子的双加帽杂多铌酸盐的合成、结构及表征武贺臣;张泽霖;李丽;王勇;马鹏涛【摘要】在水热条件下,成功合成了一例基于Keggin型多酸阴离子的双加帽杂多铌酸盐[Ni(en)3]3[Ni(en)2(H2O)2]2H[VNb12O40(VO)2]·10H2O(1),并通过红外光谱、热重分析和X射线单晶衍射等方法对该化合物进行了表征.X射线单晶衍射分析表明,化合物1属于正交晶系,Pna2(1)空间群,晶胞参数a=3.0517(3)nm,b=1.5610(1)nm,c=2.2719(3)nm,V=10.823(3)nm3.化合物1包含1个Keggin型聚阴离子[VNb12O40(VO)2]11-和3个镍配离子.在阴离子结构中,中心钒原子被12个铌原子包围形成经典Keggin型结构的[VNb12 O40]15-阴离子,另外两个{VO}基团分别加帽于[VNb12 O40]15-阴离子的两端.%A new Keggin heteropolyoxoniobate[Ni(en)3]3[Ni(en)2(H2O)2]2H[VNb12O40(VO)2] ·10H2O (1) has been synthesized by hydrothermal method, and was characterized by IR spectrum, thermogravimetric ( TG) analysis and X-rays diffraction. X-ray structural analysis indicates that com-pound 1 crystallizes in the orthorhombic Pna2(1) space group with the cell constants:a = 3.0517(3) nm, b = 1.5610(1) nm, c = 2.2719(3) nm, V = 10.823(3) nm3. Compound 1 consists of a bi-capped Keggin polyanion [ VNb12 O40( VO) 2 ] 11-and three nickel-complexes as the countercations. The polyanion can be described as a decorated Keggin cluster with one vanadium atom as the central het-eroatom surrounded by twelve niobium atoms along with two {VO} groups capping two opposite sides.【期刊名称】《化学研究》【年(卷),期】2017(028)005【总页数】5页(P563-567)【关键词】杂多铌酸盐;双加帽;Keggin型;晶体结构【作者】武贺臣;张泽霖;李丽;王勇;马鹏涛【作者单位】河南大学化学化工学院,河南开封475004;河南省实验文博学校,河南郑州450002;河南大学化学化工学院,河南开封475004;河南大学化学化工学院,河南开封475004;河南大学化学化工学院,河南开封475004【正文语种】中文【中图分类】O614.5多金属氧酸盐(Polyoxometalates，简称多酸)由于具有独特的结构和化学物理性能，在众多领域如催化、磁性、药物和光电材料等方面具有潜在的应用前景，已经成为无机化学科学中发展最快的领域之一[1-2]. 目前，多酸化学的研究和发展仍主要集中在多钨氧酸盐、多钼氧酸盐和多钒氧酸盐等方面，原因主要是它们在酸性条件下容易制备并能够在较大的pH范围内稳定存在[3-4]. 多铌氧酸盐(PONs)作为多金属氧酸盐一个重要分支，由于其合成方法较为苛刻则相对进展缓慢. 近年来，多铌氧酸盐在抗病毒、核燃料处理、生物污染物分解和催化光解水等方面展现出良好的应用价值，吸引着越来越多国内外化学工作者的关注[5].多铌氧酸盐可以分为同多铌酸盐和杂多铌酸盐. 近些年来，一系列以{Nb6}、{Nb10}、{Nb20}、{Nb24}、{Nb27}、{Nb31}和{Nb32}等为代表的新型同多铌盐酸盐等被报道出来，与之相比，杂多铌酸盐合成条件更为苛刻(反应温度高、可控pH范围小)，报道的例子相对较少[6]. 2002年，NYMAN课题组合成首例经典Keggin型杂多铌酸盐{[Ti2O2][SiNb12O40]}12-以来，Keggin型杂多铌酸盐及其衍生物相继被报道，即[TNb12O40]16-(T=Si，Ge)，[Nb2O2][TNb12O40]10-(T=Si，Ge)，[T2(TOH)2Nb16O54]14-(T=Si，Ge)，[TNb18O54]n-(T=Si，Ga和Al)，[GeNb12O40(NbO)]13-，[TNb12O40(VO)]n-(T=Ge，P)，[TNb8V4O40(VO)]11-(T= P，V)，[PNb12O40(VO)6]3-和[VNb12O40(NbONO3)2]11-[7-22]. 然而，大多数Keggin型杂多铌酸盐以Si，Ge和P为中心杂原子，以V原子为中心构筑的Keggin型杂多铌酸盐及其衍生物却鲜有报道. 众所众知，钒和铌在元素周期表中位于同一主族，具有相似的物理和化学性质，因此钒作为一种杂原子构筑稳定的V/Nb杂多氧酸盐有很大的研究空间.总体来说，基于Keggin型多酸阴离子的杂多铌酸盐已经有一些报道，但Keggin 型双加帽杂多铌酸盐的报道仅为个例. 在本文中，我们选择K7[HNb6O19]·13H2O和KVO3在水热条件下进行反应，并用扩散法培养晶体，成功合成了一例基于Keggin型多酸阴离子的双加帽杂多铌酸盐[Ni(en)3]3[Ni(en)2(H2O)2]2H[VNb12O40(VO)2]·10H2O (1)，并对其进行了红外光谱，热重分析和晶体结构表征.所用试剂均为市售分析纯产品，用前未进一步纯化. 红外光谱用Bruker VERTEX 70型傅立叶红外光谱仪测定，记录范围为2 000～450 cm-1，KBr压片. 热分析数据用Metter-Toledo TGA/SDTA851e型差热热重分析仪在N2氛围中测量(升温速率10 ℃/min，升温范围25～1 000 ℃).将K7[HNb6O19]·13H2O(0.137 g，0.1 mmol)和KVO3(0.055 g，0.4 mmol)溶于10 mL蒸馏水中均匀搅拌(溶液A)；在另一烧杯中，称取Ni(NO3)2·6H2O(0.174 g，0.6 mmol)溶解于0.83 mL水中后加入0.13 mL乙二胺，随后将该混合溶液滴加至溶液A中，并用2 mol/L LiOH溶液调节pH = 10.50，而后转移至23 mL聚四氟乙烯内衬的反应釜中，放入烘箱中，160 ℃反应72 h后过滤得到黄棕色溶液，再用扩散法培养晶体(体积比H2O∶CH3CH2OH=3∶1)，一个月左右得到棕色块状晶体，产率为12% (以K7[HNb6O19]·13H2O为基准).选取尺寸大小为0.19 mm×0.18 mm×0.17 mm棕色块状单晶封装在毛细管中，置于Bruker Apex-II CCD 衍射仪上，以石墨单色器的Mo Kα射线(λ = 0.071 073 nm)为辐射源，在296(2) K温度下测试，以ω-2θ扫描方式收集衍射数据. 晶体的结构采用直接法解出，数据经Lp因子和Multi-scan吸收校正. 所有非氢原子坐标采用直接法获得，并经过全矩阵最小二乘法优化，所有重原子(V、Ni、Nb等原子)采用各向异性热参数修正，结晶水数量通过热重分析确定. 所有计算均使用SHELXL-97程序来完成[23]. 该化合物的晶体学数据列于表1，主要键长和键角数据列于表2. (CCDC号: 1561463).单晶衍射分析表明，化合物1为正交晶系，Pna2(1)空间群. 化合物分子由1个[VNb12O40(VO)2]11-阴离子(图2a)、3个[Ni(en)3]2+配离子、2个[Ni(en)2(H2O)2]2+配离子、1个质子和10个结晶水组成(图1). 在[VNb12O40(VO)2]11-阴离子中(图2b)，中心的V原子和外围的12个Nb原子通过V-O键和Nb-O键连接形成具有Keggin结构的[VNb12O40]15-阴离子，另外两个V原子分别加帽于[VNb12O40]15-阴离子的上下两侧. 化合物1中，所有的铌原子均为六配位的八面体构型，中心的V原子和两个帽位的V原子分别为四配位的四面体构型和五配位的三角双锥构型(图2c和d).根据配位方式的不同，Nb-O键可以分为四类：Nb-Ot(0.172 5～0.185 8 nm)；Nb-μ2-O(0.185 8～0.201 8 nm)；Nb-μ3-O(0.200 7～0.215 0 nm)；Nb-μ4-O(0.244 7～0.249 7 nm). 镍配离子中的Ni原子均为六配位的八面体构型，按其配位环境的不同可以分为两类：(1)Ni1、Ni2和Ni4离子与三个乙二胺分子中的六个氮原子配位；(2)Ni3和Ni5离子分别与两个乙二胺分子上的四个氮原子和两个水分子中的氧原子配位. 键价计算表明[24]，化合物1阴离子中心V为+5价，两个加帽的V原子为+4价.如图3所示，化合物1在874 cm-1处出现的振动峰归因于Nb-Ot伸缩振动，743、699、631、497 cm-1四处出现的振动峰归属为桥氧Nb-Ob-Nb的特征振动；化合物1与原料K7HNb6O19·13H2O的红外光谱相比，Nb-Ob-Nb的特征振动峰均有不同程度的红移和劈裂，这可能是由于该结构失去了Lindqvist型[Nb6O19]8-的骨架. 化合物1在1 031 cm-1处的振动峰归属于乙二胺中CN键的特征振动，与游离的乙二胺(1 068 cm-1)相比[17]，峰的位置发生了偏移，可能是由于镍离子与乙二胺分子发生了配位作用引起的.图4为化合物1的热重分析曲线. 从图4可知，化合物1在25～1 000 ℃范围内表现为三步失重，实际总失重为30.9%. 第一步失重发生25～130 ℃之间，失重约为5.8%，对应于10个结晶水的失去. 第二步失重发生131～414 ℃之间，失重约为14.4%，对应于4个配位水和7个乙二胺分子的失去. 第三步失重在415～1 000 ℃范围内实际失重为10.7%，对应于半个结构水分子和剩余6个乙二胺分子的失去.通过水热和扩散相结合的方法成功合成了一例基于Keggin型多酸阴离子的双加帽多铌氧酸盐[Ni(en)3]3[Ni(en)2(H2O)2]2H[VNb12O40(VO)2]·10H2O (1). 结果表明，在水热条件下，+5价钒可以还原为+4价，而以钒原子为中心的Keggin 型杂多铌酸盐通过另外两个钒原子加帽，降低了阴离子表面大量的负电荷，从而形成稳定的Keggin型多铌氧酸盐阴离子.【相关文献】[1] 王恩波, 李阳光, 鹿颖, 等. 多酸化学概论[M]. 长春: 东北师范大学出版社, 2009: 36-204. WANG E B, LI Y G, LU Y, et al. Outline of polyoxometalates [M]. Changchun: Northeast Normal University Press, 2009: 36-204.[2] POPE M T, MULLER A. Polyoxometalate chemistry: an old field with new dimensions in several disciplines [J]. Angewandte Chemie International Edition, 1991, 30: 34-48.[3] 于丽, 王勇, 万榕, 等. 基于[As2W19O67(H2O)]14-构筑块的单核铥夹心型化合物的合成、结构及热稳定性[J]. 化学研究, 2015, 26: 579-583.YU L, WANG Y, WAN R, et al. Synthesis, structure and thermal stability of mono-thulium sandwiched compound based on [As2W19O67(H2O)]14- unit [J]. Chemical Research, 2015, 26: 579-583.[4] JIANG C J, LESBANI A, KAWAMOTO R, et al. Channel-selective independent sorption and collection of hydrophilic and hydrophobic molecules byCs2[Cr3O(OOCC2H5)6(H2O)3]2[α-SiW12O40] ionic crystal [J]. Journal of the American Chemical Society, 2006, 128: 14240-14241.[5] 袁洋, 李芳, 付晓, 等. 一种基于Lindqvist型多酸阴离子的三维多金属铌酸盐的晶体结构[J]. 化学研究, 2011, 22: 19-24.YUAN Y, LI F, FU X, et al. Crystal structure of a new 3D polyoxoniobate based on Lindqvist type polyoxoanion [J]. Chemical Research, 2011, 22: 19-24.[6] HUANG P, QIN C, SU Z M, et al. Self-assembly and photocatalytic properties of polyoxoniobates: {Nb24O72}, {Nb32O96}, and {K12Nb96O288} clusters [J]. Journal of the American Chemical Society, 2012, 134: 14004-14010.[7] NYMAN M, BONHOMME F, ALAM T M, et al. A general synthetic procedure for heteropolyniobates [J]. Science, 2002, 297: 996-998.[8] NYMAN M, BONHONNE F, ALAM T M, et al. [SiNb12O40]16-and [GeNb12O40]16-highly charged Keggin ions with sticky surfaces [J]. Angewandte Chemie International Edition, 2004, 43: 2787-2792.[9] BONHOMME F, LARENTZOS J P, ALAM T M, et al. Synthesis, structural characterization, and molecular modeling of dodecaniobate Keggin chain materials [J]. Inorganic Chemistry, 2005, 44:1774-1785.[10] ZHANG Z, LIN Q, KURUNTHU D, et al. Synthesis and photocatalytic properties of a new heteropolyoxoniobate compound: K10[Nb2O2(H2O)2][SiNb12O40]·12H2O [J]. Journal of the American Chemical Society, 2011, 133: 6934-6937.[11] ZHANG X, LIU S X, GAO Y H, et al. Two members of the {X4Nb16O56} family (X = Ge, Si) based on [(GeOH)2Ge2Nb16H2O54]12- and [K(GeOH)2Ge2Nb16H3O54]10-[J]. European Journal of Inorganic Chemistry, 2013: 1706-1712.[12] ANDERSON T M, ALAM T M, RODRIGUEZ M A, et al. Cupric siliconiobate. Synthesis and solid-state studies of a pseudosandwich-type heteropolyanion [J]. InorganicChemistry, 2008, 47: 7834-7839.[13] HOU Y, NYMAN M, RODRIGUEZ M A. Soluble heteropolyniobates from the bottom of group IA [J]. Angewandte Chemie International Edition, 2011, 50: 12514-12517.[14] HOU Y, ALAM T M, RODRIGUEZ M A, et al. Aqueous compatibility of group IIIA monomers and Nb-polyoxoanions [J].Chemical Communications, 2012, 48: 6004-6006. [15] HOU Y, ZAKHAROV L N, NYMAN M. 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自组装及其在分析化学等方面的应用

自组装一般是在人为控制的条件下发生。

在这个过程中，体系中的基本结构单元发生自发反应，并在形成的非共价键等作用下形成构造稳定，外形规整的结构[1]。

随着自组装技术的发展，无机合成化学、无机材料化学、配位化学等分支学科中应用自组装方法进行的研究也越来越多，涉及到的相关研究内容也涵盖了金属、氧化物结构敏感催化材料的设计合成，高效能源材料，稀土化合物功能材料，分子筛及多孔材料，无机有机杂化材料，先进碳材料等研究方向[2]。

近来，阴离子配位化学一直专注于高正电荷、具有适当维度尺寸和结合位点的超分子自组装体的设计和构建，其可以通过水中的静电相互作用或氢键选择性地识别检测阴离子客体[3]；自组装领域迅速发展也为分子材料和晶体工程领域的研究提供了多种新型合成方法[4]；超分子材料领域中操纵分子集合更是一个极具吸引力的话题[5]。

1　自组装的方法1.1　自组装一般的自组装是在内部驱动力如范德华力、氢键、毛细管力或上述的某种组合的作用下以完成组装。

其它的自组装方法包括：通过将功能分子连接至表面或通过修饰现有配体来修饰纳米粒子表面；通过施加外力的方法，如通过电场、磁场等的作用，以限定颗粒的位置，直接控制颗粒的对齐方式；对于各向异性纳米粒子的组装，通过使用模板的方法以对粒子施加顺序来实现，最简单的模板是组装粒子的表面或界面[6]。

1.2　几种自组装方法介绍1.2.1　超分子自组装合成方法超分子自组装合成方法是一种在弱结合力（如氢键，静电作用和范德华力）的影响下自发构建具有特殊结构和形状的稳定结构的过程。

这种方法很大程度上受到溶剂种类、时间、超分子表面能、温度等的影响 [7]。

超分子自组装法之一的离子自组装（ionic self-assembly）主要利用库仑作用将相反电荷的基本结构单元结合在一起而进行自组装的一种方式具有普适性、简单和便宜等特点[8]。

1.2.2　层层（LbL）自组装层层自组装是一种通用的薄膜制造方法，通过互补相互作用（如静电相互作用，氢键和疏水相互作用）对各种材料进行连续吸附，给基体覆盖上聚合物、胶体、生物分子和细胞等物质而形成多层微纳米结构。

Advanced materials for tissue engineering

Advanced materials for tissueengineeringTissue engineering is a rapidly developing field that aims to address the shortage of organs and tissues for transplantation by creating new tissues and organs using biomaterials and cells. Advanced materials are crucial for tissue engineering because they provide a scaffold for cells to grow and organize into functional tissues. In this article, we will discuss some of the advanced materials used in tissue engineering and their applications.Hydrogels:Hydrogels are water-swollen crosslinked polymeric networks that have gained attention in recent years as promising materials for tissue engineering. They have unique properties that make them attractive for this application, including high water content, biocompatibility, and the ability to be easily modified. Hydrogels can also be designed to mimic the natural extracellular matrix (ECM) of various tissues.Hydrogels can be synthesized from a variety of polymers such as natural polymers like collagen and gelatin, and synthetic polymers like polyethylene glycol (PEG) and polyvinyl alcohol (PVA). These polymers are crosslinked to form a gel-like network that can be used to support and direct the growth of cells.Hydrogels have been used to create tissues such as cartilage, skin, and heart valves. They can also be used as a vehicle for drug delivery, enabling the release of drugs at a specific location.Nanofibers:Nanofibers are fibers with diameters in the nanometer range. They have a high surface area to volume ratio, which allows for increased cell attachment and proliferation. Nanofibers can be used to create scaffolds for tissue engineering by electrospinning, aprocess where a polymer solution is electrostatically charged and then drawn to form a fiber.Nanofibers can be synthesized from both natural and synthetic polymers. Natural polymers used include collagen, chitosan, and silk, and synthetic polymers used include polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and polyurethane (PU).Nanofibers have been used to create tissues such as bone, skin, and nerve. They can also be used as wound dressings and as a vehicle for drug delivery.Scaffold-free approaches:Scaffold-free approaches aim to create tissues without the use of a scaffold. These approaches rely on the self-assembly of cells into three-dimensional structures. Cells are first isolated and expanded in culture, and then they are induced to aggregate and form a tissue.Scaffold-free approaches have several advantages over scaffold-based approaches. First, they do not require the use of synthetic materials, which can potentially be harmful to the body. Additionally, they allow for the creation of tissues with a higher degree of complexity and functionality.Scaffold-free approaches have been used to create tissues such as cartilage, liver, and blood vessels. They have also been used in the development of organoids, miniature organs that can be used for disease modeling and drug testing.Conclusion:Advanced materials have greatly advanced the field of tissue engineering, enabling the creation of functional tissues and organs. Hydrogels, nanofibers, and scaffold-free approaches are just some of the materials used in tissue engineering. As the field continues to evolve, new materials and approaches will be developed, bringing us closer to the goal of creating functional tissues and organs for transplantation.。

有序纳米材料

self-assembly of oriented attachment
Lidan, School of Chemistry & Chemical Engineering
4
Self-assembly of microemulsion
Structure of surfactant
The structure of surfactant: there is at least one hydrophilic group in the head, along with one hydrophobic group in the tail. It can be adsorbed on the surface or interface to decrease its surface energy in low concentration.
schematic of micelle
Lidan, School of Chemistry & Chemical Engineering
6
Microemulsion method is also known as
surfactant template method. It mainly utilize this property that surfactant can aggregate in solution to form micelle (or reserve micelle), microemulsion (or reserve microemulsion), liquid crystal and vesica, which have ordered microstructure. Most of these microstructures are often nanosized. It can not only provide special condition and serve as micro-reactor, but also be used as template. Now, oxides, halides, chalcogenides, metals, polymers, inorganic salts, and other nanostructured materials have been made through surfactant template method (microemulsion method).

亚铁氰化钾,铁氰化钾和双偶极半菁衍生物静电自组装膜的研究.pdf

2006年　10月第42卷　第5期北京师范大学学报(自然科学版)Journal of Beijing Normal University (Natural Science )Oct.2006Vol.42　No.5亚铁氰化钾、铁氰化钾和双偶极半菁衍生物静电自组装膜的研究3俞丹霞　朱志强　吴　涛　王科志(北京师范大学化学学院,100875,北京)摘要　通过交替沉积K 4[Fe (CN )6](或K 3[Fe (CN )6])和双偶极半菁(Me 2NC 6H 4CHCHC 5H 4N +CH 2C 6H 4—C 6H 4—CH 2—+NC 5H 4—CHCH —C 6H 4—NMe 2)的氯化物,制备了2种无机有机杂化自组装膜.通过紫外可见吸收光谱、偏振可见吸收光谱和循环伏安图对薄膜进行了表征.关键词　亚铁氰化钾;铁氰化钾;双偶极半菁衍生物;自组装膜3国家自然科学基金资助项目(20371008,90401007);北京师范大学本科生科学研究基金资助项目通讯作者收稿日期:2006205208 Decher [1]发展的以静电作用力为驱动,将阴、阳离子交替沉积吸附而制备自组装膜的技术,具有制备方法简单、厚度可控、性质稳定和高度的分子水平组装能力,因而广受关注.将功能性基团引入超薄膜一直是人们关注的研究领域.半菁是一类具有潜在应用前景的二阶非线性光学和光电转换材料[223].本文设计合成了一种新的双偶极半菁衍生物(结构见图1,简写为ACl 2).分别选择带4和3个负电荷的亚铁氰化钾和铁氰化钾作为阴离子,通过与半菁阳离子A 2+的静电自组装,制备了2种无机有机杂化的超薄膜.目的在于研究电荷对于静电自组装膜制备的影响.图1　ACl 2的分子结构1　实验部分1.1　仪器与试剂　澳大利亚G BC Cint ra 10e 紫外可见光谱仪;p HS3型酸度计;CH I 420电化学分析仪,采用三电极系统,覆盖有自组装膜的ITO 玻璃为工作电极,支持电解质为0.5mol ·L -1的Na 2SO 4溶液(p H =1.93).半菁化合物(ACl 2)按文献[2,4]方法合成;所有其他试剂均为分析纯.1.2　自组装多层膜的制备　分别用V (H 2SO 4,18mol ·L -1)∶V (H 2O 2,w =30%)=3∶1和V (N H 3·H 2O ,w =25%)∶V (H 2O 2,w =30%)∶V (H 2O )=1∶1∶5溶液对石英基片进行预处理.ITO 玻璃用氢氧化钠的饱和乙醇溶液预处理.预处理后的石英或玻璃基片按图2所示的途径,先按文献[5]方法进行表面硅烷化和氨基质子化后,依次分别浸入1.0mmol ·L -1K 4[Fe (CN )6]水溶液25min 和1.0mmol ·L -1ACl 2的水溶液中30min 或1.0mmol ·L -1K 3[Fe (CN )6]溶液25min 和1.0mmol ·L -1ACl 2的水溶液中40min.每次取出后用p H =3.00的去离子水超声振荡清洗,空气吹干.重复(2),(3)过程即可得到(K 4[Fe (CN )6]/ACl 2)n 和(K 3[Fe (CN )6]/ACl 2)n 静电自组装多层膜.2　结果与讨论2.1自组装膜的成膜条件　这2种膜的组装过程主要包括:基片的预处理和硅烷化;在静电力的作用下,[Fe(CN )6]4-(或[Fe (CN )6]3-)和ACl 2交替沉积在基片表面.其中,K 4[Fe (CN )6](或K 3[Fe (CN )6])和ACl 2溶液的浓度、p H 值及浸入溶液中的时间是膜制备过程中3个主要因素.溶液的p H 应保证基片表面氨基完全质子化,且[Fe (CN )6]4-(或[Fe (CN )6]3-)和ACl 2能够稳定存在.根据对(SiW 12/1,102DAD )n 多层膜成膜条件的研究[627],我们采用p H =3100的成膜和成膜后的漂洗液,在固定成膜溶液的浓度为1.0mmol ·L -1时,研究了基片的浸入时间对成膜的影响.结果(图3)表明:对于([Fe (CN )6]4-/ACl 2)n 薄膜,基片浸入[Fe Ⅱ(CN )6]4-溶液的时间为25min ,浸入ACl 230　第5期俞丹霞等:亚铁氰化钾、铁氰化钾和双偶极半菁衍生物静电自组装膜的研究511　图2　[Fe (CN )6]4-/ACl 2多层膜组装过程min 时,薄膜的吸光度达到恒定.而对([Fe (CN )6]3-/ACl 2)n 薄膜,[Fe Ⅲ(CN )6]3-和ACl 2浸入时间分别为25和40min 时,薄膜的吸光度达到恒定.图3　ACl 2的吸光度A 与浸入时间t 的关系a.[Fe Ⅲ(CN )6]3-;b.[Fe Ⅱ(CN )6]4-.图4　各溶液与膜的紫外可见光谱左图:ACl 2水溶液(┅),9层膜(K 4[Fe (CN )6]/ACl 2)9(…),K 4[Fe (CN )6]水溶液(—);右图:ACl 2水溶液(┅),9层膜(K 3[Fe (CN )6]/ACl 2)9(…),K 3[Fe (CN )6]水溶液(—).2.2　紫外可见光谱　ACl 2水溶液、9层自组装膜(K 4[Fe (CN )6]/ACl 2)9,(K 3[Fe (CN )6]/ACl 2)9和K 4[Fe (CN )6],K 3[Fe (CN )6]的紫外可见光谱见图4.比较可见,薄膜与ACl 2水溶液的吸收特征相似.ACl 2水溶液在355nm 处的吸收峰在薄膜中消失,在(K 4[Fe (CN )6]/ACl 2)9薄膜中469和260nm 处的特征吸收峰分别红移了18和9nm.虽然K 3[Fe (CN )6]在200～600nm 间有多个特征吸收峰,但因其摩尔消光系数很小,膜(K 3[Fe (CN )6]/ACl 2)9在484和269nm 处的吸收还主要是ACl 2的贡献,且较ACl 2水溶液分别红移了15和9nm.在膜(K 4[Fe (CN )6]/ACl 2)9和(K 3[Fe (CN )6]/ACl 2)9中观察到的相对ACl 2水溶液的红移,说明高电荷量的阴离子能明显地诱导半菁阳离子J 聚体的形成[8].图5为不同层数的(K 4[Fe (CN )6]/ACl 2)n 多层膜的紫外可见光谱.由图可见,不同层数薄膜的吸收峰位置基本保持不变,表明层间分子的相互作用不随膜层数的增加而变化;而在268和483nm 处的A 随膜层数的增加而线性增加(见图5内插图),这表明(K 4[Fe (CN )6]/ACl 2)n 多层膜已被成功组装,且膜的沉积是均匀的、可重复的.由插图483nm 处的直线斜率可知,单层膜的A =1.3×10-2,根据朗伯比尔定律可推出半菁阳离子的表面浓度Г=10-3A/ε=5.3×10-10mol ·cm -2(ε为ACl 2水溶液的摩尔消光系数,单位为L ·mol -1·cm -1).图6为不同层数的(K 3[Fe (CN )6]/ACl 2)n 多层膜　512　北京师范大学学报(自然科学版)第42卷图5　(K 4[Fe (CN )6]/ACl 2)n 多层膜的紫外可见光谱(插图为不同波长的吸光度A 与层数N 的关系)的紫外可见光谱.可见,与前一多层膜一样,膜的沉积也是均匀的、可重复的.由插图485nm 处的直线斜率可知,单层膜的A =2.7×10-2,同样也可算出表面浓度Г=10-3A/ε=1.1×10-9mol ·cm -2.图6　K 3[Fe (CN )6]/ACl 2多层膜的紫外可见光谱(插图为不同波长的吸光度A 与层数N 的关系)2.3　偏振可见吸收光谱　在入射光和基片的法线间的夹角α=30°时,测定了薄膜水平和垂直偏振的可见吸收光谱.结果表明,薄膜的可见吸收光谱表现出明显的偏振依赖性,分子排列有明显的2维有序性.通过485nm 下水平偏振的吸光度A h 和垂直偏振的吸光度A v 之比,根据方程式(1)可求得半菁离子的偶极距在(K 4[Fe (CN )6]/ACl 2)7中与基片法线间的夹角γ=45.9°[9],而在(K 3[Fe (CN )6]/ACl 2)7中的γ=53.8°.1-10-A h 1-10-A v=1+(2ct g 2γ-1)×sin 2α(1)2.4　电化学性质　图7内插图为ITO 玻璃基片上[Fe Ⅱ(CN )6]4(在100～900mV ·s -1的扫描速率下的循环伏安曲线.由图可见,在峰电位U 为0.32V 附近出现了1个阳极峰,阳极峰电流I pa 与扫描速率v 成正比(图7),表明该氧化还原过程为表面控制过程[10212].图7　一层[Fe (CN )6]4-离子循环伏安扫描速率v 与阳极峰电流I pa 的关系(插图为循环伏安曲线)依据I p 与通过电极的电子数n ,扫描速率v ,电极面积A ,法拉第常数F ,气体常数R 和绝对温度T 间的关系[10]:I p =(n F )2A Гv4R T.(2)求得[Fe Ⅱ(CN )6]4-离子的Γ=1.2×10-11mol ·cm -2,单分子占有面积为13.8nm 2.在同样的实验条件下,[Fe Ⅲ(CN )6]3-的电化学性质则不如[Fe Ⅱ(CN )6]4-稳定,易发生表面脱落.笔者曾多次实验,都无法得到较好的、可重复的循环伏安曲线.一层薄膜K 4[Fe (CN )6]/ACl 2和K 3[Fe (CN )6]/ACl 2的循环伏安实验得到的I p 与没有半菁分子层时相比均有所减少,说明沉积在外层的半菁阳离子阻碍了部分[Fe Ⅱ(CN )6]4-离子氧化还原反应的发生.3　结论研究表明,半菁阳离子与铁氰酸根和亚铁酸根离子的2种自组装膜都可均匀、平稳的沉积,2种薄膜的　第5期俞丹霞等:亚铁氰化钾、铁氰化钾和双偶极半菁衍生物静电自组装膜的研究513成膜性质的比较列于表1中.相对于半菁阳离子水溶液的吸收光谱,2种薄膜中半菁阳离子的吸收都发生了明显的红移,归因于半菁阳离子J聚体的形成.含高电荷的铁氰酸根的膜中半菁阳离子的表面浓度明显大于含亚铁酸根离子膜.循环伏安图的结果表明:2种薄膜的氧化还原特性与预料中的表面控制行为相符,半菁阳离子会阻碍阴离子发生氧化还原反应.对于薄膜的非线性光学等性质研究正在进行中.表1　K4[Fe(CN)6]/ACl2和K3[Fe(CN)6]/ACl2自组装膜性质的比较阴离子[FeⅡ(CN)6]4-[FeⅢ(CN)6]3-ACl2最佳沉积时间t/min3040成膜后ACl2吸λ260/nm99收峰红移情况λ469/nm1815多层膜中半菁离子表面浓度Γ/(mol·cm-2)5.3×10-10 1.1×10-9半菁离子的偶极距与基片法线夹角γ/(°)45.953.84　参考文献[1]　Decher G,Hong J D.Buildup of ultrathin multilayerfilms by a self2assembly process:Ⅱ.consecutive adsorption of anionic and cationic bipolar amphiphiles and polyelectrolytes on charged surfaces[J].Makromol Chem,Macromol Symp,1991,46:321[2]　Wang Kezhi,Huang Chunhui,Xu Guangxian,et al.Preparation,characterization,and second harmonic generation of a Langmuir Blodgett film based on a rare earth coordination compound[J].Chem Mater,1994,6: 1986[3]　Wang Zhongsheng,Huang Chunhui,Huang Yanyi,etal.A highly efficient solar cell made f rom a dye2modified ZnO2covered TiO2nanoporous electrode[J].Chem Mater,2001,13:678[4]　Wang Kezhi,Huang Chunhui,Xu Guangxian,et al.Optical properties of Langmuir2Blodgett film of hemicyanine containing the rare earth complex anion Dy(BPMP HD)-2[J].Thin Solid Films,1994,252:139 [5]　Haller I.Covalently attached organic monolayers onsemiconductor surfaces[J].J Am Chem Soc,1978,100: 8050[6]　Wang Kezhi,G ao Lihua.Hybrid self assembled multi2player film formed by alternating layers of H4SiW12O40 and1,10diaminodecane(DAD)[J].Mater Res Bull, 2002,37:2447[7]　Gao Lihua,Wang Kezhi.Hybrid self assembledmultilayer films formed by alternating layers of Keggin polyoxometalates and1,10DAD[J].Chin Chem Lett, 2003,14:513[8]　Andrea L,G lauco P.J2Aggregation of an anionicoxacarbocyanine in electrostatically self assembled multilayers[J].Thin Solid Films,2006,496:585[9]　Schwartz H,Mazor R,Khodorkovsky V,et al.Langmuir and Langmuir2Blodgett films of NLO active22 (p2N2alkyl2N2methylamino)benzylidene21,32indandiones2π/A curves,uv2vis spectra,and SH G behavior[J].JPhys Chem B,2001,105:5914[10]　Bard A J,Faulkner L R.In Electrochemical methods,fundamentals and applications[M].New Y ork:Wiley,1980:5222523SE LF2ASSEMB L ED MU L TILAYER FILMS FORMED BY K4[Fe(CN)6], K3[Fe(CN)6]AN D A BIPOLAR HEMICYANINE DERIVATIVEYu Danxia　Zhu Zhiqiang　Wu Tao　Wang Kezhi(College of Chemistry,Beijing Normal University,100875,Beijing,China)Abstract　Two self2assembled multiplayer films are successf ully prepared by alternating adsorption of ferrocyanide or ferricyanide,and a bipolar hemicyanine dichloride of Me2NC6H4CH CHC5H4N+C H2C6H4—C6H4—C H2—+NC5H4—CH CH—C6H4—NMe2.The films are st udied by means of UV2visible absorp2tion spect roscopy,polarized visible absorption spect ro scopy and cyclic voltammetry.K ey w ords　ferrocyanide;ferricyanide;hemicyanine;self2assembled film。

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Journal of Power Sources 195 (2010) 703–709Contents lists available at ScienceDirectJournal of PowerSourcesj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /j p o w s o urSelf-assembly of highly charged polyelectrolyte complexes with superior proton conductivity and methanol barrier properties for fuel cellsSerpil Yılmaztürk,Hüseyin Deligöz ∗,Mesut Yılmazo˘g lu,Hakan Damyan,Faruk Öksüzömer,S.Naci Koc ¸,Ali Durmus ¸,M.Ali GürkaynakIstanbul University,Engineering Faculty,Chemical Engineering Dept.,34320Avcilar-Istanbul,Turkeya r t i c l e i n f o Article history:Received 26May 2009Received in revised form 4August 2009Accepted 18August 2009Available online 25 August 2009Keywords:Layer-by-Layer (LbL)Membrane Self-assemblyDirect methanol fuel cell Proton conductivitya b s t r a c tThe paper is concerned with the formation of Layer-by-Layer (LbL)self-assembly of highly chargedpolyvinyl sulfate potassium salt (PVS)and polyallylamine hydrochloride (PAH)on Naﬁon membrane to obtain the multilayered composite membranes with both high proton conductivity and methanol blocking properties.Also,the inﬂuences of the salt addition to the polyelectrolyte solutions on mem-brane selectivity (proton conductivity/methanol permeability)are discussed in terms of controlled layer thickness and charge density.The deposition of the self-assembly of PAH/PVS is conﬁrmed by SEM analysis and it is observed that the polyelectrolyte layers growth on each side of Naﬁon membrane regularly.(PAH/PVS)10–Na +and (PAH/PVS)10–H +with 1.0M NaCl provide 55.1and 43.0%reduction in lower methanol permittivity in comparison to pristine Naﬁon,respectively,while the proton conductivities are 12.4and 78.3mS cm −1.Promisingly,it is found that the membrane selectivity values (˚)of all multilayered composite mem-branes in H +form are much higher than those of Na +form and perﬂuorosulfonated ionomers reported in the literature.These encouraging results indicate that composite membranes having both superior proton conductivity and improved methanol barrier properties can be prepared from highly charged polyelectrolytes including salt for fuel cell applications.© 2009 Elsevier B.V. All rights reserved.1.IntroductionDirect methanol fuel cells (DMFC)are expected to become important power sources for transport and portable applications due to their high energy density and simpliﬁed design [1–3].The commercialization of DMFC and micro-DMFC is limited by the high cost of the platinum catalyst and methanol cross-over across polymer based membrane [4,5].The major limitation of the commercially available perﬂuorosulfonated membranes is that for direct methanol fuel cells they exhibit signiﬁcant methanol cross-over from anode to cathode which causes a mixed potential and reduces the electrical performance.Therefore,to reach high per-formance membranes,methanol permeability should be reduced.In this respect,some approaches,such as use of diluted methanol and operation at low temperatures,were studied and reported a signiﬁcant decrease in DMFC performance [6,7].Another approach to suppress methanol cross-over is the modiﬁcation of ﬂuori-nated and non-ﬂuorinated membranes (PBI,sPEEK etc.)through the addition of inorganic components.This approach can dramatically reduce the methanol cross-over with slightly sacriﬁcing the pro-∗Corresponding author.Tel.:+902124737070/17758;fax:+902124737180.E-mail address:hdeligoz@.tr (H.Deligöz).ton conductivity.For this purpose,there is very intensive research activity in the modiﬁcation of Naﬁon based composite membranes such as Naﬁon–silica [8–10],Naﬁon–zirconium phosphate [11],Naﬁon–cesium ions [12]and Naﬁon–polymer composites.Recently conductive polymers,polyaniline (PANi),polypyrrole (PPy)and polybenzimidazole (PBI)were introduced into Naﬁon to limit the methanol permeability [13–16].In an alternative approach for blocking methanol permeation effectively,various multilayered composite membrane structures were investigated.In these stud-ies,polyvinyl alcohol (PVA)and polyether ether ketone (PEEK)were used as thin barrier ﬁlms on Naﬁon [17,18]and it was reported that the methanol permittivity value dramatically decreased due to the formation of thick barrier ﬁlm on Naﬁon membrane with sacriﬁcing the proton conductivity.Layer-by-Layer (LbL)method consists of alternate dipping of the membrane support in oppositely charged polycation and polyan-ion electrolyte solutions,as reported by Decher and other groups [19–21].The versatility,simplicity and ﬂexibility of the build-up process are the main advantages of this deposition technique for the surface modiﬁcation.Tieke and co-workers have reported many works on LbL assembled composite membranes showing high selective ion permeation and separation factor [22–25].Up to now,the use of LbL method for the preparation of multilay-ered composite membrane was studied scarcely.Recently,Farhat0378-7753/$–see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.jpowsour.2009.08.044704S.Yılmaztürk et al./Journal of Power Sources195 (2010) 703–709and Hammond have reported that the deposition of a polyelec-trolyte multilayer membrane on a porous support using the LbL technique and they offered LbL technique as an alternative method to fabricate a membrane-electrode assembly[26].In another study, Jiang et al.have reported that poly(diallyldimethylammonium chloride)(PDDA)/poly(styrene sulfonic acid)(PSS)was deposited on Naﬁon1135membrane by LbL and observed that the methanol cross-over current density signiﬁcantly decreased with an increase in the number of deposited layer[27].In our recent study, we optimized the LbL deposition conditions for polyallylamine hydrochloride(PAH)/PSS system in order to achieve both high pro-ton conductivity and methanol blocking properties simultaneously [28].On the other hand,transport mechanism of alcohol and pro-ton through Naﬁon-like perﬂuorosulfonated ionomer depending on the ion type and equivalent weight of membranes was discussed by Okada et al.in detail[29–32].So far,the inﬂuences of external salt addition to polyelectrolyte dipping solution and use of highly charged polyelectrolyte,PVS,on fuel cell performance have not been reported.In the present study,it is aimed to demonstrate the inﬂu-ences of use of highly charged polyelectrolytes and salt addition to polyelectrolyte solution on proton conductivity and methanol per-meability of the LbL self-assembled Naﬁon-composite membrane. The relation of the thermal,conductive and methanol permeation properties was analyzed with the thickness,charge density and charge type of deposited polyelectrolyte bi-layers.2.Experimental2.1.MaterialsPolyallylamine hydrochloride(PAH)(Mw:15,000)and polyvinylsulfate potassium salt(PVS)(Mw:170,000)were supplied from Aldrich and used as received.Naﬁon®117com-mercial membrane was received from Aldrich Company(175␮m) with a nominal equivalent weight of1100g equiv.−1.Sulfuric acid (95–98%),hydrogen peroxide(35%)and methanol(99.7%purity) were obtained from Riedel de Haen,NaCl was supplied from Fluka. Mili-Q ultrapure water was used in all deposition experiments and AC measurements(Milipore18.2M at25◦C).Prior to deposition, Naﬁon membrane was treated according to the procedure reported previously[28].For the preparation of self-assembled multilayered composite membranes,the dipping method reported by Tieke et al.was used[15]and described in our recent paper[28].2.2.CharacterizationThe formation of the LbL self-assembled multilayers on mem-brane surface prepared from PAH/PVS was conﬁrmed by Scanning Electron Microscopy(SEM).In SEM analysis,dried composite mem-brane was manually fractured after cooling in liquid nitrogen.The sample was sputtered with gold and palladium mixture in10nm thickness and measured by a JEOL/JSM-6335F instrument at an operation voltage of5kV.Proton conductivity( )of the LbL self-assembled composite membranes was measured by two-probe AC method using a Solartron1260Frequency Response Analyzer(FRA) and Solartron1296Dielectric Interface.The membrane was cut in 2cm×2.5cm dimensions and impedance measurements were per-formed in water at22±1◦C.The test system used was described in our recent paper[33].Methanol permeation measurements of the LbL composite membranes were carried out at22±1◦C by using a U-shaped home-made apparatus which consists of two dif-ferent compartmentsﬁlled with20mL of ultrapure Mili-Q water and10M methanol solution.The concentration of methanol dif-fused through the composite membrane was detected by using a Zeissler refractive indexer and the methanol permeation rate was calculated as explained in our recent study and literature[28]. TG measurements of the samples were carried out with a Seiko EXSTAR6000-TGA/DTA6300model instrument.TG curves were recorded of the multilayered composite membranes in acid form (PAH/PVS)n–H+and in sodium form(PAH/PVS)n–Na+at a heating rate of10◦C min−1under a nitrogen atmosphere in the temperature range of40–800◦C.Ion exchange capacity(IEC)values of Na+and H+form of self-assembled composite membranes were determined by titration method[33].A sample membrane in proton form was soaked in saturated NaCl solution for48h at room temperature to exchange H+with Na+.Then,H+released into the solution was titrated with a0.01N NaOH solution using phenolphthalein as the indicator.IEC was calculated by using the following formula:IEC=VMm dry(1) where IEC is the ion exchange capacity expressed in mequiv.g−1; V is the added titrant volume at the equivalent point expressed in mL,M is the molar concentration of the titrant and m dry is the dry mass of the sample expressed in g.2.3.Preparation of Na+and H+form of multilayered composite membranesFirstly,PAH and PVS were dissolved in Mili-Q water in a con-centration of10−1and10−2moles L−1,respectively.The pH of the polyelectrolyte solutions was adjusted to1.8by adding aqueous HCl.The solutions of PAH and PVS contained NaCl in concentration of1moles L−1was prepared to observe the salt effect.The prepa-ration of ultra thin polyelectrolyteﬁlms starts with the immersion of,e.g.,a positively charged substrate in an aqueous solution of an anionic polyelectrolyte so that a thin layer of this compound is adsorbed and the surface charge of the substrate reverted.Sub-sequent dipping of this substrate into a solution of a cationic electrolyte again leads to adsorption of a thin layer and the sur-face charge is rendered positive again.Multiple repetition of the adsorption steps leads to a multilayerﬁlm with alternating posi-tive and negative excess charges.Finally all prepared LbL composite membranes in Na+form were inverted into H+form by immersing into1N HCl for1h.The adsorption steps were repeated up to10 times for methanol permeation measurements and from5to20 times for AC conductivity tests.Five bi-layers deposited PAH/PVS Naﬁon-composite membranes in Na+and H+form were donated as (PAH/PVS)5–Na+and(PAH/PVS)5–H+,respectively.For comparison, Naﬁon®117(EW=1100)was also tested as a reference membrane.3.Results and discussionThe structure of the multilayerﬁlms is strongly based on the deposition conditions such as concentration of adsorbing species, adsorption time,concentration and type of added salt,and tem-perature.The most frequently used control parameters are the ionic strength and pH of the solution[21,34].In our recent study,we opti-mized the deposition conditions of PAH/PSS system and we found that the polyelectrolyte concentration and pH as10−1moles L−1 and1.8,respectively[28].In principle,we tried to control the deposited layer thickness and charge density by using both highly charged polyelectrolyte and salt addition to the dipping solution. During the deposition experiments and test measurements of all prepared Naﬁon-composite membranes,no physical change was observed.Even when20bi-layers of PAH/PVS was deposited on the membrane support,the obtained composite membrane was clear and highly mechanically stable as well as pristine Naﬁon.S.Yılmaztürk et al./Journal of Power Sources195 (2010) 703–709705Fig.1.SEM picture of(PAH/PVS)30Naﬁon-composite membrane.3.1.SEM picture of the multilayered composite membraneAlthough the easiest way to follow multilayer build-up is UV–vis spectroscopy[21,35],this technique could not be used because non-presence of UV active groups in PAH/PVS polyelectrolyte system.That is why SEM picture of the multilayered compos-ite LbL membrane prepared from PAH/PVS was taken in order to observe the multilayer formation and it is depicted in Fig.1.As it is seen from theﬁgure,it was conﬁrmed that the multilayers were formed on both sides of surface modiﬁed Naﬁon membrane homogenously.The thickness of30bi-layers of PAH/PVS deposited Naﬁon-composite membrane is0.375␮m.In other words,one deposition cycling of PAH/PVS gives a deposited layer roughly in 100nm thickness.As it is known from the literature,the thicknesses of formed bi-layers mainly depend on the deposition conditions such as pH,concentration of dipping solution,charge density of polyelectrolytes,dipping time and external salt addition[20,21,28].3.2.Proton conductivity( )of the multilayered composite membraneIn the present study,we expected to improve both proton con-ductivity( )and methanol blocking properties simultaneously by using highly charged polyelectrolytes with salt.For this purpose, the inﬂuence of monovalent salt(NaCl)addition to the dipping solution on fuel cell performance parameters(proton conductivity, methanol permittivity)of LbL self-assembled composite mem-brane was systematically studied and the results were listed in Tables1and2depending on the number of adsorbed bi-layers.The parameters affecting the proton conductivity of the membranes are Table1Comparison of the proton conductivity( )values of(PAH/PVS)n depending on the number of deposited bi-layers.Multilayeredcomposite membraneNumber of depositedbi-layers(n)(mS cm−1)at22±1◦C PAH/PVS561.271049.582039.82Naﬁon®117–37.78Fig.2.Nyquist plots of(PAH/PVS)n(n=5,10,20)without salt.deﬁned in the following formula.=nFC H+ H+(2) where n is an electric charge of carrier protons and equal to1+,F is Faraday constant(96,485×104C mol−1),C H+is the concentration of the carrier proton and H+is the mobility of carrier proton.Thus the proton conductivity of a membrane mainly is inﬂuenced by both of concentration and mobility of the carrier proton.For comparison, the proton conductivity of the pristine Naﬁon®117membrane was calculated in our test system and found to be37.7mS cm−1with two-probe techniques.This result is in good agreement with the reported data in the literature[36].3.2.1.Inﬂuences of charge density(q c)and salt addition to the dipping solution depending on the deposition number ofmultilayersFig.2shows the Nyquist plots of(PAH–PVS)n(n=5,10and20) without salt.Also,the calculated proton conductivity values are depicted in Table1.As it is seen from Table1,the conductivity val-ues of all LbL self-assembled composite membranes prepared fromTable2Comparison of the proton conductivity( ),methanol permeability(P M)and membrane selectivity(˚)values of the LbL self-assembly of composite membranes prepared from PAH/PVS with1.0M NaCl depending on the number of deposited bi-layers and ion type.Multilayered composite membrane Number of deposited bi-layers(n) (mS cm−1)at22±1◦C P M×107(cm2s−1)a(˚)b(S s cm−3)×10−4 PAH/PVS with1M NaCl(Na+form)57.18 3.27(45.8%) 2.201012.42 2.71(55.1%) 4.582015.87––PAH/PVS with1M NaCl(H+form)568.84 4.16(31.1%)16.551078.27 3.44(43.0%)22.762092.54––Naﬁon®117–37.78 6.04 6.25a Percent improvement in methanol barrier properties was given in paranthesis.b Membrane selectivity( /P M).706S.Yılmaztürk et al./Journal of Power Sources195 (2010) 703–709Fig.3.Nyquist plots of(PAH/PVS)n–Na+(n=5,10,20)with1M NaCl.PAH/PVS free salt were higher than that of pristine Naﬁon®117. This improvement can be explained by the increase in the number of carrier proton.One can also see from Table1that the pro-ton conductivities of(PAH–PVS)5and(PAH–PVS)20were61.3and 39.8mS cm−1,respectively.This reduction in proton conductiv-ity with the number adsorbed bi-layers may be explained by the formation of thicker bi-layers which can limit the mobility of car-rier proton.Interestingly,proton conductivity value of PAH/PVS system was nearly2times higher than obtained from PAH/PSS system due to the high charge density of PVS.The charge den-sity(q c)is expressed in terms of the number of ion pairs per number of carbon atoms in the repeating unit of the complex formed by the polycation and polyanion.While q c of the PAH/PVS system is0.2,this value for PAH/PSS system is only0.09.Thus the preparation of composite membranes with highly charged polyelectrolytes caused an improvement in the number of carrier proton which will promote proton conduction along the mem-brane[37].As it is known from the literature,the charge density of the polyelectrolytes depends not only on the molecular struc-ture but also on the degree of ionization of the polar groups.The ionization strongly depends on the pH of the aqueous polyelec-trolyte solution as it is shown in our recent work and the literature [28,34].In order to explore the variation in proton conductivity as a func-tion of salt addition to the polyelectrolye solution,the build-up of multilayers was examined by the presence of salt.For this purpose, it is especially preferred for more concentrated salt addition(1M) in order to obtain composite membranes with higher proton con-ductivity and membrane selectivity values.The Nyquist plots of multilayered composite membrane in Na+form were depicted in Fig.3and the calculated conductivity values were listed in Table2. As it is seen from Table2,the proton conductivity of Na+form in multilayered composite membrane was lower than that of pris-tine Naﬁon®117.This reduction in conductivity is attributed to the low mobility of the inverted Na form by ion exchange reaction. For conﬁrmation,we calculated the IEC values of the both pris-tine Naﬁon andﬁve/ten bi-layers deposited of PAH/PVS composite membranes in Na+form and found that IEC values were sharply decreased from0.87to0.08and0.07mequiv.g−1,respectively. Thus IEC results conﬁrmed our explanation of salt concentration effect.Another explanation may be the lower water uptake in the case of Na+form of multilayered composite membranes which may suppress the mobility of charge carrier species and limit the pro-ton conductivity.As it is known from the literature,the mobility of the cation is affected by the water content or the volumefractionFig.4.Nyquist plots of(PAH/PVS)n–H+(n=5,10,20)with1M NaCl.of water in the membrane[30].The cationic conductivity in the composite membrane is determined by two major factors that are the amount of residing water in the ionic channel and the interac-tion between cations and sulfonic acid groups.Furthermore,with an increase in the number of adsorbed bi-layers,the proton con-ductivity of the composite membranes was slightly increased and reached to15.9mS cm−1for(PAH/PVS)20–Na+with1.0M salt.The reason might be that the larger thickness prevents the oppositely charged polyelectrolyte chains from complete interpenetration and neutralization of their charges.In that case more excess charges are present in the membrane,which may effectively conduct the protons along the membrane.3.2.2.Inﬂuences of ion form in multilayered compositemembranes depending on the deposition number of multilayers The effect of ion type in the PAH/PVS multilayered composite membrane on the proton conductivity was investigated by invert-ing the LbL composite membrane from Na+form to H+form.Fig.4 shows the Nyquist plots of(PAH–PVS)n–H+(n=5,10,20)with1.0M NaCl.The proton conductivity values of the composite membrane in H+form were6–10times larger than those of Na+form.This large increase in proton conductivity value is mainly attributed to higher mobility of the H+form than that of Na+form.This result is well agreed with the Okada’s study[29].In this study, they reported that the mobility of H+form was6–9times larger than that of other alkali cations.Also,another explanation may be that Na+are less hydrophilic than H+and cause a lower amount of water absorption as compared with H+.This would result in the smaller volume of hydrophilic domains inside the membrane which will cause lower ionic mobility.Okada et al.have reported some important reports on the transport mechanism of perﬂuoro-sulfonated membranes with H+form,alkali metal cation and binary cation systems.Proton conductivity values of H+form composite membrane were provided by two transport mechanisms,i.e.,Grot-thuss and vehicle mechanisms like reported earlier by Okada et al.[31].Our results are in good agreement with the transport data given in the literature[31,38,39].Contrarily PAH/PVS free salt sys-tem,the proton conductivity of all composite membranes in H+ form have exhibited an increase with the number of deposited layers.Consequently,it can be concluded that the proton conductiv-ity of the LbL Naﬁon-composite membrane in H+form prepared from polyelectrolytes with salt was signiﬁcantly improved and reached to a value which is nearly3times higher than pristine Naﬁon®117.S.Yılmaztürk et al./Journal of Power Sources195 (2010) 703–709707Fig.5.An idealized scheme of multilayer formation upon alternating Layer-by-Layer assembly of PAH and PVS on Naﬁon membrane which inhibits methanol cross-over and the chemical structures of the polyelectrolytes used.3.3.Methanol permeation(P M)across multilayered composite membranesHighly methanol permeation(P M)through the proton conduct-ing polymer membrane is a very important problem to be solved for DMFC applications.In Naﬁon based membranes,methanol diffusion rate and the proton conductivity are in a trade-off rela-tionship with each other,i.e.,the membrane having higher proton conductivity shows higher alcohol cross-over.As we know from the literature,generally,alcohols penetrate into the hydrophilic regions in the membranes,which suggest the formation of ionic cluster regions consisting of alcohols,protons,and sulfonic acid groups.Since alcohols and proton both transport through the ionic cluster regions,the expansion of the diffusion space by swelling results in their faster diffusion.Because alcohols move in the expanded space by the vehicle mechanism,the membrane swelling is another important factor for the fast diffusion.The other param-eter affecting the methanol permittivity through the membrane is the channel structure of ionic cluster regions and/or the interaction with sulfonic acid groups.Thus,the channel structure of the ionic cluster regions prevents fast alcohol diffusion in the membranes [27,32].In another study,it is reported that the cationic form of the Naﬁon membrane strongly inﬂuences on the methanol and water permeability values.The water and methanol permeability values of the Naﬁon membranes decrease in the cation form which has higher atomic number[40].It is expected that blocking the hydrophilic ionic domains,which are primarily associated with–SO3−clusters on the Naﬁon mem-brane surface,and closing of the channels of Naﬁon membrane would effectively suppress methanol cross-over.Therefore,we tried to plug these pores and block the hydrophilic domains by the formation of thicker multilayeredﬁlms on the surface of treated Naﬁon for limiting the methanol permeability in this study.The proposed mechanism is depicted in Fig.5which shows the plug-ging of special channels of Naﬁon membrane by the formation of bi-layers in different thickness.Methanol permeation was measured using a home-made U-shaped two chamber apparatus described in detail previously in Section2.2[28].Prior to testing,each membrane,whose area was 2cm2,was soaked in ultra pure water for1h at room tempera-ture.The methanol concentration in ultra pure water compartment was signiﬁcantly increased and then reached a plateau over30h. Therefore all methanol permeation tests were carried out during this time.3.3.1.Inﬂuences of salt addition to the dipping solutiondepending on the deposition number of multilayersThe permeation rates(P)of methanol through the composite membranes consisting of different number of bi-layers of PAH/PVS with NaCl are given in Table2.In our experimental system, methanol permeation rate was found to be6.04×10−7cm2s−1 for Naﬁon®117at22◦C,which compares well with those of 4.8×10−6and5.6×10−6cm2s−1measured at60and70◦C,respec-tively[24].It is seen that Na+form of the LbL self-assembled membranes have exhibited signiﬁcant lower methanol perme-ation values than that of pristine Naﬁon due to the formation of multilayeredﬁlms.(PAH/PVS)5–Na+and(PAH/PVS)10–Na+con-taining1.0M NaCl on Naﬁon enabled methanol permeability of the membrane to decrease by45.9%(3.27×10−7cm2s−1)and55.1% (2.71×10−7cm2s−1),respectively.The methanol permeation rates of the composite membranes with salt dramatically decreased with the number of adsorbed bi-layers.The main reason for this signiﬁcant reduction in the methanol permeability is the larger thickness of the individual polyelectrolyte layers which provides closing the pores more effectively.Another explanation may be lower hydrophilicity of Na+form of composite membrane which causes a signiﬁcant reduction in water and methanol transport.We also compared the methanol permeability value of the LbL compos-ite membrane depending on the salt presence and we found that (PAH/PVS)5–Na+with1.0M NaCl exhibited nearly2times higher methanol barrier properties than that of the membrane prepared by the polyelectrolyte solutions without salt[28].3.3.2.Inﬂuences of charge density(q c)and ion form inmultilayered composite membranes depending on the deposition number of multilayersTo observe the effect of ion form in multilayered composite membrane,methanol permeation tests of the composite mem-branes in proton form were carried out and the results compiled in Table2.The methanol blocking properties of(PAH/PVS)5–H+and (PAH/PVS)10–H+with1M NaCl were improved by31.1and43.0% compared to Naﬁon®117,respectively.Interestingly,it is expected that the methanol permittivity is inversely proportional to q c.Thus the methanol permittivity is high when highly charged polyelec-trolyte was used instead of weak polyion.However,it is found that the methanol blocking properties were signiﬁcantly improved with the number of adsorbed bi-layers prepared from highly charged polyelectrolytes.This can be explained by the formation of thicker708S.Yılmaztürk et al./Journal of Power Sources195 (2010) 703–709Fig.6.TGA curves of(PAH/PVS)n(n=5,10)and(PAH/PVS)n–H+(n=10,20)with 1.0M NaCl depending on the number of deposited bi-layers.multilayers which can plug the pores of the Naﬁon more effectively than that of less thicker membrane.3.4.Thermogravimetric analyses(TGA)of the multilayered composite membranesCommercially available perﬂuorinated membranes have a lim-ited range of working temperature for fuel cell applications.In order to investigate the inﬂuence of multilayer formation and charge type in multilayered composite membrane on thermal stability,TG anal-yses of the membranes in H+and Na+form were carried out and TG curves are depicted in Fig.6depending on the number of deposited bi-layers.The detailed TGA results are also given in Table3.Fig.6shows TG curves of(PAH–PVS)n–H+(n=10,20)with1M NaCl and(PAH-PVS)n(n=5,10)without salt comparatively.The TG traces of the multilayered composite membrane in H+and Na+ (not shown)exhibited different proﬁles.Decomposition of the pre-pared composite membrane in proton form has occurred mainly in three steps related to a water loss(i),side chain group(–SO3H) decomposition(ii)and backbone decomposition(iii),respectively, while composite membrane in Na+form has degraded in one step. Theﬁrst degradation step of Naﬁon®117membrane has started at 293.5◦C and10%weight loss occurred at346.6◦C.Subsequently, the degradation of perﬂuorosulfonated backbone has completed at 542.9◦C.Similar curves were obtained by Surowiec and Bogoczek in the investigation of Naﬁon®117acid form[41].The composite membranes prepared from polyions free salt have exhibited nearly the same TG patterns compared to pristine Naﬁon.The thermal degradation of(PAH/PVS)n–Na+occurred in only one stage and the onset temperature was roughly150◦C higher than thatobserved parative membrane selectivity(˚)values of the multilayered composite membranes depending on the number of deposited bi-layers and ion type.for(PAH/PVS)n–H+.This is attributed to the formation of sodium salt of PVS by ion exchange reaction.As it is known from the literature,the water content of the membranes decreases progres-sively with increasing counter charge density and indicating that (PAH/PVS)n–Na+presents lower water loss due to their large ionic radii[42,43].On the other hand,the thermal behavior of PAH/PVS deposited Naﬁon-composite membrane in acid form is similar to pristine Naﬁon®117due to the fully inversion of ions from Na+to H+form.As a consequence,it can be concluded that the thermal properties of the LbL self-assembled composite membrane depend on the water content,cation size and ion type in multilayered struc-ture.3.5.Membrane selectivity of the multilayered composite membranesFig.7shows the membrane selectivity(˚)of multilayered composite membranes comparatively.The selectivity factor(˚) is deﬁned as the ratio of proton conductivity to methanol per-meability and used as an indicator of the suitability of a given membrane for DMFC application[44].All the prepared Naﬁon-composite membranes in H+form had3–4times higher membrane selectivity than that of Naﬁon®117(6.25×104S s cm−3).The mem-brane selectivity of(PAH/PVS)10–H+with1.0M NaCl system was improved and reached to nearly22.8×104S s cm−3.Lower selec-tivity for Na+form of composite membrane is attributed to its low proton conductivity which is almost2times lower than pris-tine Naﬁon.Evaluated membrane selectivity results obtained in the present study are higher than those reported in the literature [13,14].Another promising result is that the membrane selectivity of LbL multilayered composite membrane prepared from PAH/PVS was higher than that of PAH/PSS system due to high charge den-sity of PVS.Conclusively,we expect that the membrane selectivityTable3TGA results of(PAH/PVS)n,(PAH/PVS)n–Na+and(PAH/PVS)n–H+with1.0M NaCl depending on the number of deposited bi-layers and ion type.Multilayered composite membrane Number of deposited bi-layers(n)T i(◦C)T10(◦C)T50(◦C)T f(◦C)(PAH/PVS)n5291.9334.3469.7559.910299.6352.7485.4551.7 (PAH/PVS)n–Na+with1M NaCl5423.9469.0487.0540.010436.2468.0489.2542.320448.6467.2507.0544.4 (PAH/PVS)n–H+with1M NaCl10302.3328.8493.3554.420298.8322.7492.5558.9 Naﬁon®117–293.5346.6471.3542.9[T i]refers to initial temperature where degradation of sulfonic acid groups in the membrane has occurred;[T10]refers to temperature where10%of weight loss has occurred; [T50]refers to temperature where50%of weight loss has occurred;[T f]refers to temperature where degradation of the samples has completed.。