jp101661t ABS文献

Dynamics of Phase Separation in Poly(acrylonitrile-butadiene-styrene)-Modified Epoxy/DDS System:Kinetics and Viscoelastic EffectsP.Jyotishkumar,†Ceren O¨zdilek,‡Paula Moldenaers,‡Christophe Sinturel,§Andreas Janke,|Ju¨rgen Pionteck,|and Sabu Thomas*,†,⊥School of Chemical Sciences,Mahatma Gandhi Uni V ersity,Priyadarshini Hills,Kottayam,Kerala686560,India;Department of Chemical Engineering,Catholic Uni V ersity of Leu V en,de Croylaan,46,B-3001,Leu V en,Belgium;Centre de Recherche sur la Matie`re Di V ise´e,UMR6619CNRS Uni V ersite´d’Orle´ans,1B Rue de la Fe´rollerie,FR45071,Orle´ans Cedex2,France;Leibniz Institute of PolymerResearch Dresden,Hohe Str6,DE01069,Dresden,Germany;and Centre for Nanoscience andNanotechnology,Mahatma Gandhi Uni V ersity,Priyadarshini Hills,Kottayam,Kerala686560,IndiaRecei V ed:February24,2010;Re V ised Manuscript Recei V ed:September19,2010The dynamics of phase separation andfinal morphologies of poly(acrylonitrile-butadiene-styrene)(ABS)-modified epoxy system based on diglycidyl ether of bisphenol A(DGEBA)cured with4,4′-diaminodiphe-nylsulfone(DDS)have been monitored in situ throughout the entire curing process by using optical microscopy(OM),differential scanning calorimetry(DSC),rheometry,and small-angle laser light scattering(SALLS).The evolution of phase separation andfinal morphologies with substructures were explored by OM.Thefinalmorphologies of the blend cured at150and165°C are of phase-inverted type and are quite different fromthefinal morphologies of the same blend cured at180°C,in which thefinal morphologies are cocontinuous.AFM observations of the fully cured sample confirmed the existence of three different phases,the epoxycontinuous phase,SAN(styrene/acrylonitrile)continuous phase,and PB droplets at the interface,with a strongtendency to stay at SAN continuous phase.Furthermore,the continuous epoxy phase contains SAN particlesand the continuous SAN phase contains epoxy particles.Cure kinetics and rheological results correspondwell with the viscoelastic phase separation revealed by OM.The SALLS results display clearly that thephase separation takes place according to nucleation and growth mechanism followed by spinodaldecomposition.The development of light scattering patterns during the second stage phase separation followsthe Cahn-Hilliard model of spinodal demixing.Furthermore,the evolution of the scattering vector followsa Maxwell-type relaxation equation establishing the viscoelastic behavior of phase separation.The relaxationtime of phase separation can be described by the Williams-Landel-Ferry equation for viscoelasticity.As awhole,the dependence of phase separation on cure temperature and the development offinal morphologiesand the associated mechanisms were explored in detail for the complex epoxy/ABS system.1.IntroductionThe viscoelastic effects on phase separation and the evolution of phase morphology in thermoset-thermoplastic blends have attracted increased attention due to their great significance to optimize the mechanical properties.Systems such as polysul-fone-modified epoxy,1polyoxymethylene-modified epoxy,2etc. have been studied.On mixing thermoplastic with epoxy resin, one can obtain a homogeneous or heterogeneous mixture.Upon curing,phase separation starts immediately due to the increase in molecular weight of the epoxy resin,which results in a thermodynamically unstable system.3Tanaka and Araki reported that viscoelastic effects play a crucial role in phase separation for the blends with dynamic asymmetry.4-6In other words, viscoelastic effects on phase separation originate from the dynamic asymmetry in the relaxation and diffusion of molecular chains,which may be due to large difference in the T g and molecular weight of the blend components.7,8The phase separation may take place through two main mechanisms,which are nucleation and growth(NG)or spinodal decomposition (SD).9-14SALLS,OM,DSC,and rheology are the most imperative techniques to explore the phase separation behavior of polymer blends.15-17Apart from the evolution of phase separation,the curing reaction in epoxy/DDS/ABS blends is accompanied by chemical reactions and physical transformations from gelation to vitrifica-tion and hence results in a complex kinetic behavior and deserves a detailed exploration.In comparison with thermo-plastics,the processing of thermosets and thermoset matrix composites is more complicated and less controlled because of their reactivity.In these processes,polymer synthesis and shaping take place in a single operation:this involves the conversion of liquid monomers or polymers into solid cross-linked polymers.18The mechanism and kinetics of cure deter-mine the network morphology,which in turn decides the physical and mechanical properties of the cured product.The viscosity is a very important parameter to characterize accurately the process conditions and to visualize the gelation and vitrification transition state.19Thus,the knowledge of rheological*To whom correspondence should be addressed.Phone:+91-481-2730003.Fax:+91-481-2731002.E-mail:sabupolymer@,sabuchathukulam@.†School of Chemical Sciences,Mahatma Gandhi University.‡Catholic University of Leuven.§UMR6619CNRS Universite´d’Orle´ans.|Leibniz Institute of Polymer Research Dresden.⊥Centre for Nanoscience and Nanotechnology,Mahatma GandhiUniversity.J.Phys.Chem.B2010,114,13271–132811327110.1021/jp101661t 2010American Chemical SocietyPublished on Web10/06/2010and curing behavior of the resin system is particularly necessary to control the processing and subsequent engineering design.20 Moreover,the rheological analysis is indispensable tofind out the relationship between conversion,phase separation,and viscosity evolution for the process simulation.19For thermoset-ting systems in industrial applications,it is important to establish relations of transition phenomena to the reaction time at different cure temperature so that desired properties can be controlled.21 Furthermore,the study of mechanism of phase separation and the evolution of scattering vector(q)are very important to establish the effect of viscoelastic behavior on the resulting morphologies and properties.The cure temperature and polymer molecular weight are important factors influencing the thermodynamic and kinetic aspects of phase separation and thus thefinal morphology of the epoxy blends.However,the influence of cure temperature and polymer molecular weight on the phase separation has not been extensively studied to date.Moreover,the mechanism of phase separation is not fully understood for epoxy/ABS thermoplastic blends.In this paper,our focus is to understand the mechanism of phase separation in epoxy/ABS blends by considering all the above points.As shown in our previous publications,there is a high dependence of the cure kinetics andfinal morphologies on the thermoplastic concentration.13,22 Recently,we have also recognized that,for the epoxy blend system containing12.9wt%ABS,phase separation takes place by the combination of both NG and SD mechanism with a well-defined phase inversion process.14The main objective of this work is to investigate the affect of temperature and viscoelastic effects on the dynamics of phase separation of an ABS-modified epoxy system.For that purpose,a time-resolved study of the phase separation was carried out by OM,DSC,rheology,and SALLS.2.Experimental Section2.1.Materials Used.The matrix material used in the experiments consists of diglycidyl ether of bisphenol A(DGE-BA)(Lapox L-12,Atul Ltd.,India.)and4,4′-diaminodiphenyl-sulfone(DDS)(Lapox K-10,Atul Ltd.,India).The epoxy content in Lapox L-12varies between5.25and5.40eq/kg. Lapox L-12has a viscosity of about1.15-1.2g/cm3.DDS is a white powder with a melting point of178°C.It has a pot life of about75-115min at25°C.The toughener ABS(Poly lac PA-757K)was manufactured by Chi Mei Corp.,Taiwan.The used poly(acrylonitrile-butadiene-styrene)(ABS)is a com-mercially available thermoplastic polymer consisting of70wt %polystyrene(PS),25wt%acrylonitrile(AN),and5wt% polybutadiene(PB).The molecular weight of the soluble part of ABS was determined to be M n)51300g/mol and M w) 125200g/mol(PDI)2.44,GPC,PS standard)and the density was determined to be1.051g/cm3by means of an helium pycnometer.2.2.Preparation of Blends.The epoxy/ABS blend contain-ing12.9wt%ABS was prepared by mixing20g of ABS with 100g of DGEBA at180°C under constant stirring.After proper mixing,35g of DDS was added to epoxy/ABS mixture corresponding to a stoichiometric epoxy:amine ratio of2:1.The freshly prepared mixtures were immediately used for the analysis.2.3.Characterization Techniques.2.3.1.Optical Micros-copy.A few milligrams of the epoxy/ABS system placed between two glass slides were observed by a Leitz laborlux12 Pols optical microscope,while the sample was being cured in a Linkam CSS450shearing cell.The Linkam cell was only used for heating;no shear was applied.Digital micrographs were taken at several times by a Hamamatsu TSU digital camera controller C4742-95.2.3.2.Differential Scanning Calorimetry.The calorimetric measurements were performed on a Perkin-Elmer Pyris DSC6 differential scanning calorimeter.The instrument was calibrated with indium and dry cyclohexane standards.Dry nitrogen was used as purge gas and samples of15-20mg were analyzed. Dynamic DSC was done at2.5,5,7.5,and10°C/min from20 to350°C for the neat epoxy resin/DDS mixture.Isothermal measurements were done at150,165,and180°C.The curing was assumed to be completed when the isothermal curve leveled off to a straight line.The areas under the peaks during the isothermal cure were used to determine the conversion R at various times.The conversion R)∆H t/∆H tot,where∆H t is the heat of cure at time t,calculated by the integration of the DSC isothermal signal,and∆H tot is the total heat of cure of the neat epoxy resin calculated by the integration of DSC dynamic signal.2.3.3.Oscillatory Shear Rheology.The viscoelastic proper-ties of the epoxy blends during isothermal curing were determined by oscillatory shear measurements performed on an ARG2rheometer(TA Instruments).Each sample was placed on aluminum parallel plates of25mm in diameter,which were of disposable type.Temperature control was achieved by an ETC system(environmental testing chamber)suitable for studying the polymer melts in the temperature range-160to 600°C under a N2atmosphere.The experiments were carried out with5%strain and an angular frequency of1Hz and were used to determine G′,G′′,tanδ,and complex viscosity.2.3.4.Small-Angle Laser Light Scattering(SALLS).The small-angle light scattering setup(Newport model ULM-TILT) consists of a5mW He-Ne laser(λ)638.2nm)as the scattering light source.The sample is placed between two glass slides being cured in a Linkam cell(CSS450).The distance between the sample and screen was adjusted as29cm.The laser beam passing through the Linkam cell was examined by a Pulnix camera,which was used to record the change in scattering patterns.The processing of the data was performed using the special SALLS software developed in Catholic University,Leuven,Belgium.2.3.5.Atomic Force Microscopy.The AFM measurements were done in the tapping mode by a Dimension3100Nanoscope V(Veeco,USA).We used silicon-SPM sensors(Budget Sensors,Bulgaria)with a spring constant of ca.40N/m and resonance frequency of ca.280kHz;the tip radius is lower than 10nm.2.3.6.Field Emission Scanning Electron Microscopy.The morphology of the cross-linked epoxy blend was examined using a ULTRA FESEM(model ULTRA plus,Carl Zeiss NTS GmbH,Germany).The fractured samples were smoothed with an ultramicrotome and the SAN-rubber phase(SAN)styrene/ acrylonitrile)was etched out by immersing the cut in chloroform for2h.The samples were coated with platinum by vapor deposition using a SCD500sputter coater(BAL-TEC AG, Liechtenstein).3.Results3.1.Evolution of Phase Separation by OM.Figures1,2, and3demonstrate the phase separation and evolution of phase morphologies in the ABS-modified epoxy/DDS blends cured at different temperatures,illustrating different stages of the phase separation process from the initially formed matrix droplet morphology to thefinal complex structures.Before going into the detailed mechanism of phase separation in the ABS-modified13272J.Phys.Chem.B,Vol.114,No.42,2010Jyotishkumar et al.epoxy system,it is important to mention that the T g of SAN and PB are110and-80°C,respectively,while that of epoxy monomer is-20°C and hence there is a strong dynamic asymmetry.As mentioned in the Introduction,the other important factor that contributes to the dynamic asymmetry is the difference in molecular weight.The number-average mo-lecular weights of ABS and the epoxy resin(DGEBA)were M n)51300and355g/mol,respectively.This dynamic asymmetry can play a very important role in the dynamics of phase separation and thefinal morphology.Thefinal morphologies of12.9wt%ABS-modified epoxy blends cured at150and165°C are of phase-inverted type and are quite different from thefinal morphologies of ABS-modified epoxy blends cured at180°C,in which thefinal morphology is cocontinuous.This indicates that,at temperatures higher than 165°C,the rate of phase separation is faster and,as a result, the generated epoxy domains grow faster.In later stages,the growing epoxy domains start to agglomerate,resulting in the final cocontinuous morphology,in which both SAN phase and epoxy phase are continuous.The time at which the formation of the new epoxy phase due to phase separation could be detected and is listed in Table1.The effect of temperature on the phase separation was also carefully examined using DSC, rheology,and SALLS and the results are elaborated in detail in the coming text.From the evolution of morphology and resultant final morphologies at different temperatures,it was obvious that the temperature plays a prominent role for the growth rate of phase-separated structures and the resultingfinal phase morphologies.3.2.Calorimetric Analysis.The epoxy/ABS blend was cured isothermally at three different temperatures,i.e.,150,165,and 180°C.Figure4a shows the isothermal DSC curves of neat epoxy system and the ABS-modified epoxy blend cured at150°C.A rapid increase in the reaction rate was observed whichpasses through a maximum in the exothermic heatflow.In the presence of ABS the reaction rate is reduced.However,a second increase in reaction rate was observed in the DSC curve of the ABS-containing blend.The time at which this second increment in reaction rate occurs(appearance of the shoulder)is listed in Table 1.A similar kind of acceleration phenomenon was observed by Pascault and co-workers for the blends based on polystyrene or polyetherimide in DGEBA/MCDEA(4,4′-methylenebis(3-chloro-2,6-diethylaniline))systems3and poly-(methyl methacrylate)in a DGEBA/DDS system.23To study the effect of temperature on the rate and phase separation of the blend,a comparison of curing rate vs time in the ABS-modified epoxy cured at150,165,and180°C is shown in Figure4b.The peak maximum and the shoulder are slightly shifted toward shorter cure times with increase in temperature. This reflects an increase in the reaction rate as well as the rate of phase separation at higher cure temperatures supporting the OM micrographs.This is because of the increased molecular mobility that favors the chemical interactions such that a higher number of chains are involved in the curing process and,as a consequence,both the rate of the reaction and rate of phase separation are increased.3.3.Rheological Behavior.The profile of change in complex viscosity of ABS-modified epoxy blends with time at different temperatures(150-180°C)is shown in Figure5.In general, the rheology on polymer blends is an accepted method to provide valuable information on the structure development during curing.At the beginning of the cure,the viscosity slowly increases with time and then,at a certain point,a very rapid increase is observed.Moreover,this increase in complex viscosity curves is shifted to shorter times with increase in temperature;this is because the reactions between epoxy and DDS are thermally accelerated.The reaction between epoxyFigure1.Evolution of phase morphologies of ABS-modified epoxy blends at150°C:(a)360s,(b)2220s,(c)2420s,(d)2600s,(e) 2900s,(f)3680s,and(g)9000s(800×800µm2).Figure2.Evolution of phase morphologies of ABS-modified epoxy blends at165°C:(a)480s,(b)1440s,and(c)6000s(800×800µm2).Figure3.Evolution of phase morphologies of ABS-modified epoxy blends at180°C:(a)480s,(b)960s,and(c)6000s(800×800µm2).TABLE1:Time for the Generation of New Epoxy Phase Due to Complex Phase Separationtemp(°C)time for theappearance ofsecond increasein reaction rate(shoulder)fromDSC(s)time for thegeneration of newepoxy phasefrom OM(s)time for thegeneration ofnew epoxy phasefrom rheology(s) 150244024002106 165122013801021 180760920662Phase Separation of an ABS-Modified Epoxy System J.Phys.Chem.B,Vol.114,No.42,201013273and DDS induces various chemical and physical phenomena. In fact,the resin viscosity increases and cross densification advances.The curing reaction proceeds until vitrification or until the transformation of the rubbery network into a glassy solid takes place.24-26It is well-known that the phase separation has a profound effect on the rheological behavior of the blends.It is important to mention that phase separation is triggered by the NG mechanism,which takes place immediately after mixing the curing agent into the epoxy monomer/ABS blend.14This means that phase separation may affect the curing reaction even at very low conversion but this may not be prominent.On the other hand,we have an increase in reaction rate of the epoxy amine system during the second stage of phase separation by spinodal decomposition.This means that the phase separation affects the reaction rate and hence may influence the gelation times of the epoxy blends.However,we have difficulties to predict the exact gelation times of the epoxy blends since they are always coupled with the phase separation process.We have investigated the evolution of rheological parameters such as tanδ,G′,and G′′at different temperatures;the results seem to be identical irrespective of temperature.For avoiding overlapping of the results,we are giving only the representative rheological profile obtained at150°C.Figure6reveals the rheological parameter as a function of real time/conversion scale in case of epoxy/ABS-modified epoxy cured at150°C.The rheological curves reveal a reduction in the tanδcurve during the early stages of the reaction,which may be due to dominance of SAN-rich phase(the generation of thermoplastic-rich con-tinuous phase)and is accompanied by a gradual increase in viscosity;hence,this drop in tanδcurve supports the results from OM micrographs.During the early stages of the reaction, G′is below G′′,indicating the liquid nature of the material; after some time,both G′and G′′increase rapidly.As mentioned before,this phenomenon may be due to the formation of continuous SAN-rich phase;this is followed by a crossover point where G′equals G′′which means the system acts as both elastic and viscous,storing and dissipating an identical amount of energy at this point.Pascault et al.observed a similar kind of behavior for the blends based on polystyrene(PS)or polyether-imide(PEI)in DGEBA/MCDEA systems3and poly(methyl methacrylate)(PMMA)in the DGEBA/DDS system.233.4.Phase Separation Dynamics by SALLS.The phase separation process of all modified systems was monitored in situ by SALLS.The change in scattered intensity and scattering vector(q)was recorded at appropriate time intervals during isothermal curing at135,140,150,160,165,170,and180°C. At all curing temperatures,the light scattering profile remains the same irrespective of the temperature.Figure4.(a)Curing rate against conversion plot for neat resin and epoxy/ABS blends cured at150°C.(b)Curing rate against time plot for epoxy/ABS blends cured at150,165,and180°C.plex viscosity of ABS-modified epoxy blends at150, 165,and180°C.Figure6.Storage modulus,loss modulus,and tanδvs time curves of modified epoxy blends at150°C.13274J.Phys.Chem.B,Vol.114,No.42,2010Jyotishkumar etal.Figure 7a shows the scattering intensity vs scattering vector (q )for with 12.9wt %ABS-modified blends cured at 135°C during the very early stage of phase separation.Here the scattering peaks at low q values are observable at the beginning of cure,implying the presence of microphase separation.The following factors are possible for the initiation of microphase separation:the first one could be the presence of SAN-grafted PB particles,and the PB phase in SAN-grafted PB is cross-linked and hence they are insoluble in epoxy resin.The presence of insoluble SAN-grafted PB may initiate the phase separation process.The second reason for phase separation probably from the thermal treatment of samples at the temperature as high as 180°C.These initial scattering patterns during early stages of phase separation exactly match with our previous observationsFigure 7.Scattering intensity vs scattering vector profile for the ABS-modified epoxy system cured at (a,b)135,(c)150,(d)165,and (e)180°C.Phase Separation of an ABS-Modified Epoxy System J.Phys.Chem.B,Vol.114,No.42,201013275for NG mechanism.14Figure7b shows the scattering intensity vs scattering vector(q)during the second-stage phase separation. Scattering peaks are at larger q values originating at the beginning of the second stage phase separation and are typical for SD.These peaks shift rapidly to lower q values due to epoxy phase coarsening.A clear shift of the main peak in the intermediate to late stages establishes an SD mechanism. Furthermore,a sharp increase in intensity of scattered light from the beginning of second-stage phase of separation was observed. Figure7c-e shows the scattering intensity vs scattering vector during the second-stage phase separation by SD mechanism at 150,165,and180°C,respectively.From the light scattering profiles at different temperatures,we observe a rapid shift in the scattering vector to lower values at180°C as compared to light scattering profiles at lower temperatures,establishing rapid epoxy phase coarsening by coalescence at high temperatures. This supports the facts observed by OM,DSC,and rheological measurements.Even though thefinal morphologies are different at different temperatures,the shape of the scattering profiles looks almost identical.3.5.Final Morphology by AFM and FESEM.AFM investigations were made to understand thefinal morphology in detail.According to Magonow et al.,27we choose the scan conditions(free amplitude>100nm,set-point amplitude ratio 0.8)in order to get stiffness contrast in the phase image,which means bright features in the phase image are stiffer than dark areas.Parts a and b of Figure8show the AFM micrograph of neat ABS and completely cured ABS-modified epoxy/DDS system at180°C.The AFM micrograph of ABS shows that the cross-linked PB phase is dispersed in the SAN continuous phase,indicating two-phase morphology.The dispersed PB domains consist of small agglomerates of original PB(dark phase)particles containing some(bright phase)grafted SAN. On the other hand,the AFM micrographs of the completely cross-linked ABS/epoxy blend show a very interesting morphol-ogy with three different phases:two continuous phases forming a cocontinuous structure with substructures(epoxy continuous phase containing dispersed SAN particles and the SAN continu-ous phase in which epoxy particles are dispersed)and the most important feature,the PB phase appears as dispersed small agglomerates at the blend interface between the cocontinuous structures.The driving force for the segregation at the interface between the SAN and epoxy continuous phases is the minimiza-tion of the specific interfacial energy of the system,but there is still a tendency to locate more near to the SAN phase due to the better compatibility caused by the grafted SAN part.A minor quantity of PB is dispersed in the SAN continuous phase. For the better understanding of thefinal generated complex morphology of ABS-modified epoxy/DDS system at180°C, the blend was carefully examined by FESEM.FESEM micro-graph of epoxy/ABS blend after ultramicrotome cutting followed by etching in chloroform for2h is shown in Figure8c.During the etching process,the SAN phase has been dissolved away by chloroform.FESEM micrograph of the12.9wt%ABS-containing cross-linked epoxy specimen exhibits a cocontinuous structure in which both the epoxy phase as well as the SAN phase are continuous.In the continuous epoxy phase,SAN particles are dispersed,while in the continuous SAN phase clusters of big epoxy particles were observed.These particles result from viscoelastic phase separation as described below.4.DiscussionIn general,the phase separation phenomenon in the modified epoxy blends may be interpreted as follows based on OM analysis.The system was partially miscible initially(before curing).There were only the small insoluble SAN-graft-PB particles present in the homogeneous DGEBA/DDS/SAN mixture.Because of the thermal treatment of the samples,these SAN-graft-PB particles dispersed in the homogeneous epoxy/ SAN mixture may initiate the phase separation through nucle-ation and growth mechanism.During the initial stages of phase separation,spherical SAN nuclei are found to develop in the epoxy matrix by the nucleation process.More and more SAN particles may form by NG as the curing time advances(Figures 1a,2a,3a).After a few minutes,the system transforms into a cocontinuous structure,like the one in Figure1b.The cocon-tinuous structure may come from the SD mechanism,in which both SAN-rich phase with PB particles and epoxy-rich phase are continuous.After this point,the cocontinuous structure ruptures rapidly and the SAN-rich phase with PB particles becomes the continuous phase while the epoxy phase becomes the dispersed phase,indicating a clear phase inversion at which epoxy particles develop in the SAN continuous matrix as shown in Figure1c.This transition in the phase behavior could be explained as follows.The enhancement of the concentration fluctuation makes the SAN-rich phase more elastic(due to its high molecular weight)than epoxy-rich phase such that these epoxy droplets subsequently grow by the diffusion process (Figure1d-g).During the fast growth of the epoxy phase,there may be some miscible SAN chains get separated out of the SAN-rich phase.These original miscible SAN chainsfinally phase separate due to the reduced miscibility caused by the epoxy network formation resulting in the formation of SAN substructures in the epoxy-rich matrix.On the other hand,during the phase inversion process,some epoxy will not reach the growing epoxy-rich domains since the diffusion is hampered by the highly viscous SAN surrounding.This part of the epoxy resin trapped in the SAN-rich phase separates in later stages to spherical epoxy substructures in the SAN-rich continuous phase. The immiscible PB particles are driven during this process to the interface of the bulky epoxy phase and SAN phase,with a tendency to have more contacts with the SAN phase due to the better compatibility caused by the grafted SAN part.Kyu et al. reported similar kind of complex crossover behavior of reaction-induced phase separation from NG to SD.28These observations are completely different from the simple NG mechanism advocated by Pascault et al.8,29-32and the SD process described by Inoue.12A schematic model describing the evolution of phase separa-tion based on OM,AFM,and FESEM investigations is given in Figure9.Figure9a shows the schematic representation of immiscible SAN-graft-PB particles dispersed in a homogeneous epoxy/SAN mixture.In Figure9b,the NG mechanism possibly initiated by SAN-graft-PB particles is depicted,which results in SAN particles with PB inclusions dispersed in the epoxy matrix.Figure9c shows that the change from the NG mecha-nism to the SD mechanism results in the formation of cocon-tinuous structures of both the epoxy phase and the SAN phase. Obviously,the PB will be in the SAN phase.Figure9d shows a rapid phase inversion in which the SAN phase with PB particles becomes the continuous phase and epoxy becomes the droplet.Eventually,Figure9e represents thefinal morphological structures obtained at different curing temperatures.As mentioned in the Results,thefinal morphology of ABS/ epoxy blends cured at150and165°C is of phase-inverted type and is different from thefinal morphology of blends cured at 180°C,in which thefinal morphology is cocontinuous.This effect of temperature on thefinal morphologies can be explained13276J.Phys.Chem.B,Vol.114,No.42,2010Jyotishkumar et al.。