1-s2.0-S002230931100319X-main

Effect of acid,water and alcohol ratios on sol-gel preparation of antire flective amorphous SiO 2coatingsÖmer Kesmez a ,b ,1,Esin Burunkaya a ,b ,1,Nadir Kiraz a ,b ,1,H.Erdem Çamurlu c ,d ,⁎,Meltem Asiltürk e ,2,Ertu ğrul Arpaça ,b ,1aAkdeniz University,Faculty of Science and Art,Department of Chemistry 07058Antalya,Turkey bNANOen R&D Ltd.,Antalya Technopolis,Akdeniz University Campus,07058Antalya,Turkey cAkdeniz University,Department of Mechanical Engineering,07058,Antalya,Turkey dMattek Advanced Materials Ltd.,Antalya Technopolis,Akdeniz University Campus,07058Antalya,Turkey eİnönüUniversity,Prof.Dr.Hikmet Say ılkan Research and Development Laboratory for Advanced Materials,44280,Malatya,Turkeya b s t r a c ta r t i c l e i n f o Article history:Received 7November 2010Received in revised form 4May 2011Available online 31May 2011Keywords:Sol-gel processes;Nanometric SiO 2particle;Nanometric film;Acid catalysis;Antire flective filmVarying amounts of nitric acid catalyst,water and ethyl alcohol were used in the preparation of SiO 2sols by hydrolysis and condensation reactions of tetraethyl orthosilicate in a one step acid catalysis process.Hydrolysis of TEOS was followed by FT-IR analyses.Size of SiO 2particles was seen to vary in 8–41nm range with respect to changing HNO 3and water amounts in the sols.Gelation occurred in some systems.Surfaces of films were examined by FESEM and AFM,after coating on glass substrates by dip coating.Thicknesses of the films were measured to be in the range of 80–120nm.5.6±0.2%point increase in light transmittance was obtained when HNO 3/TEOS (mol/mol)ratio of 4.74×10−4and H 2O/TEOS (mol/mol)ratio of 9.08were utilized.Sols were found to be stable for months and coatings prepared after 45days still provided 5.2±0.2%point increase in light transmittance.©2011Elsevier B.V.All rights reserved.1.IntroductionAntire flective (AR)coatings have attracted technological and scienti fic attention due to their ef ficiency enhancement bene fits in many applications such as solar panels,video display screens,eyeglasses,windows,etc.[1,2].Various materials and techniques have been utilized for obtaining AR surfaces.Chemical etching of glass [3,4],and formation of a coating layer on glass surface [5–11]are the two common methods for obtaining AR surfaces.It was shown that re flective losses can be canceled out if a layer with a thickness of a quarter of the wavelength of incident light is present on the substrate and if the refractive index (n )of this layer is equal to square root of the refractive index of the substrate.For an ordinary glass with an n of 1.52,required n is 1.23[6,12].Thus,both of the mentioned methods rely on the principle that refractive index of glass decreases with increasing porosity [5–12].A porous layer with a lower refractive index than the glass substrate can be formed on the glass surface bythe etching process.However,utilization of hazardous chemicals in this method requires waste water treatment [3,4].In the methods of forming an additional layer on glass surface,the aim is to obtain a coating with a low or adjustable refractive index and with controlled thickness [5,6].Various techniques such as CVD,sputtering and sol-gel dip,spin or spray coatings are employed for preparing an AR coating on glass.Dip-coating of the sol-gel synthesized colloidal solutions appears to be more convenient among the other techniques.It is possible to control the pore size,distribution and volume fraction of porosity in the formed coating by altering the parameters of sol-gel process.Additionally,sol-gel process utilizes chemicals that are harmless to the environment such as water,ethanol and silica particulates.It has scale-up possibility,ease of coating complex shapes,and lower equipment cost as compared to other methods [5,13,14].In most of the studies,porous silica has been utilized for obtaining AR films on the glass surface with a controlled refractive index,thanks to its environmental stability and durability [5].Focus of investiga-tions was on control of pore size and volume fraction for adjusting the refractive index of the SiO 2films.In the sol-gel colloidal SiO 2coating process,porosity is related to particle size and distribution of the SiO 2sol from which the film is obtained [7],as well as to the curing temperature of the coating on glass [5,8,13,15].Size distribution of oxide nanocrystals was reported to have a crucial affect on enhancing various properties [16].SiO 2particles were mostly formed throughJournal of Non-Crystalline Solids 357(2011)3130–3135⁎Corresponding author at:Makine Mühendisli ği Bölümü,Akdeniz Üniversitesi,Dumlup ınar Bulvar ı,Kampüs,07058Antalya,Türkiye.Tel.:+902423106346;fax:+902423106306.E-mail address:erdemcamurlu@ (H.E.Çamurlu).1FEF Kimya Bölümü,Akdeniz Üniversitesi,Dumlup ınar Bulvar ı,Kampüs,07058Antalya,Türkiye.2İnönüÜniversitesi FEF Kimya Bölümü,44280,Malatya,Türkiye.0022-3093/$–see front matter ©2011Elsevier B.V.All rights reserved.doi:10.1016/j.jnoncrysol.2011.05.003Contents lists available at ScienceDirectJournal of Non-Crystalline Solidsj ou r n a l h o me pa g e :ww w.e l s ev i e r.c o m/l oc a t e /j no n c r ys o lhydrolysis and condensation of alkoxysilanes such as tetramethy-lorthosilicate (TMOS)[8]or tetraethyl orthosilicate (TEOS)[9,10,15]with addition of water,alcohol and acid or base catalyst.In order to adjust the porosity and therefore the refractive index of SiO 2particulate film,factors such as type and amount of catalyst and aging duration of sol [5,7,15,17–19],alkoxide to water ratio [20],type of alcohol [21],type of acid [15],baking temperature of the film [8]have been investigated.Effect of pH was investigated by Brinker et al.and a two-step method was suggested.In this method initially acid catalyzed TEOS,water,ethanol system was prepared and then base (NH 4OH)-water mixture was added [22].Addition of basic catalyst into acid catalyzed system was suggested to increase the rate of condensation.Condensation kinetics is faster than hydrolysis kinetics when base catalysts are used.Acid catalysis was proposed to form linear or randomly branched chains.On the other hand,formation of a network of uniform particles takes place as a result of base catalysis [23].Two-step catalysis reactions based on similar route proposed by Brinker et al.were employed commonly [7,23,24].Vincent et al.reported that increasing the base catalyst amount enhances the growth of SiO 2particles [24].Acid catalyst resulted in the smallest particle size of SiO 2among the investigated systems.Effects of different acid types on SiO 2sols and films were investigated by Fardad [15].Films obtained from H 2SO 4and H 3PO 4catalyzed sols exhibited different behavior than those obtained from HCl,HNO 3and C 2H 2O 4catalyzed sols,in terms of refractive index,volume fraction of porosity and thickness of the films.The difference was attributed to the change in hydrolysis and condensation rates with respect to type of acid [15].Kesmez et al.investigated the effect of different base catalysts and effect of aging duration in acid and base catalyzed sols [7].It was shown that not only pH,but also type of the catalyst is effective in controlling the hydrolysis and condensation kinetics [7,23].It was reported that base catalysis provided a very fast SiO 2particle growth and that the increase in the light transmittance provided by the obtained films presented a fluctuating character with respect to aging duration of the sols.Due to the high growth rate of SiO 2particles,thickness of the obtained films increased and light transmittance initially decreased by increasing aging duration of the sols.Further increase in SiO 2particle size and film thickness resulted in a re-increase in transmittance.Obtained sols were seen to be useful for 1–3days after preparation,indicating their very short shelf-life.On the other hand,films prepared from solely acid catalyzed sols presented stable and enhanced light transmittance values,in the investigated aging duration of 22days [7].Shelf life of the SiO 2sol is an important issue for industrial applications.Present study focuses on preparation of sols with long shelf life,from which films having enhanced light transmittance can be obtained.For this purpose,sols were prepared with single step acid catalysis (HNO 3),by altering the amounts of HNO 3and water.Size distribution of the SiO 2particles and light transmittance of the films which were composed of the prepared particles were evaluated,andeffects of water and acid catalyst amount on SiO 2particle size,on film thickness and on light transmittance properties were explored.2.Experimental procedureSiO 2sols were prepared by hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS,Fluka Chemicals,N 98%)in the presence of nitric acid (HNO 3,Merck Chemicals,65%).Sample codes,amounts of acid catalysts and water used in the systems are presented in Table 1.For the preparation of AR1sol,0.132mol TEOS was mixed with 1.167mol EtOH and the mixture was heated at 70°C.In another beaker,6.26×10−4mol HNO 3was mixed with 1.364mol H 2O and this acid solution was added dropwise into the TEOS-EtOH mixture.Same amount of TEOS (0.132mol)was used in all the systems.The mixture was stirred at 70°C in re flux for 20h.The formed nano SiO 2colloidal sol was diluted with EtOH at a ratio of 1:3.74(w/w SiO 2/EtOH).Consequently,a sol with a SiO 2content of 1.58wt SiO 2%was obtained.The other systems given in Table 1were prepared similarly.Fourier transformed infrared spectrophotometer (ATR-FTIR;Var-ian 1000model)was used to characterize the TEOS hydrolysis.Measurements were analyzed by signal averaging 16scans at a resolution of 4cm −1.Particle size distributions of the SiO 2sols were determined by a particle size analyzer (Zetasizer Nano-ZS,Malvern Instruments).In order to investigate the optical properties,2mm thick,5×10cm soda-lime glass substrates were coated by dipping them into the SiO 2colloidal sol.Various withdrawal speeds in the range of 100–250mm/min were tested for acid catalyzed system and it was seen that the highest light transmittance was obtained when the glass substrates were withdrawn at a speed of 200mm/min from the SiO 2sol.Therefore,all of the samples were prepared at the same withdrawal speed.The coated glass samples were dried in air at room temperature and then they were calcined at 450°C for 30min.Glass samples containing nanometric SiO 2films were subjected to optical and morphological analyses.Light transmittance was measured by a hazemeter at 550nm (Haze-Guard Plus,BYK Gardner)and percent light transmittance increases provided by the SiO 2films were determined.Percent light transmittance was calculated by subtracting the light transmittance of the uncoated glass measured at 550nm by the hazemeter,from that of the SiO 2coated glasses.The percent re flection (%R)of all thin films was measured using a Varian Cary 5000model UV –Vis –NIR spectropho-tometer which was combined with diffuse re flectance apparatus (DRA)with a focusing mirror.Field emission scanning electron microscopy (FESEM)analyses were performed with a FEI Nova Nanosem unit.A PSIA XE-100E unit was utilized for atomic force microscopy (AFM)analyses.Root mean square (rms)surface roughness was evaluated from the AFM line pro file data by XEI software (PSIA Inc.).Film thicknesses were determined by Filmetrics F20-HC thin film measurement system,precision of which was speci fied as 1nm.Surface hardness tests andTable 1Amounts and ratios of HNO 3,H 2O and EtOH in the prepared sols.Specimen HNO 3(moles)TEOS (moles)H 2O (moles)EtOH (moles)HNO 3/TEOS H 2O/TEOS EtOH/TEOS H 2O/EtOH AR1 6.26×10−40.132 1.364 1.167 4.74×10−310.338.84 1.17AR2 6.26×10−50.132 1.710 1.167 4.74×10−412.958.84 1.47AR3 6.26×10−60.132 1.710 1.167 4.74×10−512.958.84 1.47AR4 6.26×10−70.132 1.710 1.167 4.74×10−612.958.84 1.47AR5 6.26×10−40.132 1.980 1.060 4.74×10−3158.03 1.87AR6 6.26×10−40.132 2.2530.954 4.74×10−317.077.23 2.36AR7 6.26×10−80.132 1.710 1.167 4.74×10−712.958.84 1.47AR8 6.26×10−50.132 1.029 1.433 4.74×10−47.8010.860.72AR9 6.26×10−50.132 2.3910.900 4.74×10−418.11 6.82 2.66AR10 6.26×10−50.132 1.199 1.366 4.74×10−49.0810.350.88AR116.26×10−40.1321.0271.4334.74×10−37.7810.860.723131Ö.Kesmez et al./Journal of Non-Crystalline Solids 357(2011)3130–3135adhesion tests of the films were carried out by an Erichsen Hardness Test Pencil 318and an Erichsen Type 295multi-cross cutter,respectively.The results of the tests were evaluated according to the ASTM D 3359protocol [25].3.Results3.1.Sol and SiO 2particle characterizationFT-IR analyses were performed during hydrolysis of TEOS in predetermined durations and it was seen that hydrolysis was almost completed in 20h.Results of FT-IR analyses performed at t=0and at t=20h are given in Fig.1.The intensity of the characteristic peak of TEOS at 964cm −1belonging to C –H rocking (CH 3in TEOS)decreases in 20h.This indicates the decrease in the amount of TEOS as a result of hydrolysis [26].The peak at 1087cm −1,which also decreases,is due to Si –O –Si symmetric stretching in linear structures and C –O asymmetric stretching (TEOS).The stretching at 1049cm −1arises from C –O symmetrical stretching in EtOH and that at 879cm −1is due to CH 3or CH 2in EtOH [27].The peak at 2300cm −1is due to CO 2which is present in the ambient atmosphere during sample preparation before ATR-FTIR measurements.Initial experiments were performed with HNO 3/TEOS (mol/mol)ratio of 4.74×10−3,by altering the H 2O/TEOS ratio in the sols as shown in Table 2.It was seen that the SiO 2particle size increased from 9±2.0nm to 17±1.5nm when H 2O/TEOS ratio was increased from 7.80to 10.33,keeping the HNO 3/TEOS ratio constant at 4.74×10−3.Particle size distribution plots of representative systems are presented in Fig.2.When the H 2O/TEOS ratio was further increased to 18.11,particle size decreased to 13±2.6nm.Experiments were continued by keeping the H 2O ratio constant at 12.95,and by altering the HNO 3ratio.It was seen that gelation of the sols took place when HNO 3ratios of 4.74×10−4M and 4.74×10−5were utilized.Further decrease in the acid ratio to 4.74×10−6or4.74×10−7resulted in formation of SiO 2particles with about 40±1.5nm average particle size.Further experiments were conducted by keeping the HNO 3ratio at 4.74×10−4and by changing the H 2O ratio.First,H 2O/TEOS ratio was increased to 18.11from 12.95and gelation still occurred as shown in Table 2.Then,when H 2O ratio was decreased to 9.08,monomodal SiO 2particle size distribution was observed with 30nm average particle size.Further decreasing the H 2O ratio to 7.80with 4.74×10−4HNO 3ratio resulted in formation of SiO 2particles having bimodal particle size distribution.80vol.%of the particles had 20±2.0nm size,and 20vol.%of them had 300±5.0nm size.Particle size of AR10system was measured as prepared and after 45days of preparation.The SiO 2particle size only slightly changes in 45days of aging as can be seen in the particle size distribution plots given in Fig.3.Average SiO 2particle size was measured as 34±2.6nm after 45days.This result indicates that the prepared sols have quite a long shelf life and they can be used after long durations of their preparation.SiO 2nanoparticles obtained by the employed synthesis method have amorphous structure [30].3.2.Film characterizationAverage particle size of the sols which were prepared with various HNO 3and H 2O amounts is presented in Table 3,together with the thickness values of the films obtained from these sols.In some of the solutions,gel formation was observed to occur during preparation of the sols while mixing under re flux.Particle size and thicknesses were not reported for these systems in Tables 2and 3.The films were obtained by employing a withdrawal speed of 200mm/min.Samples were cured at 450°C for ½h.Formed films are expected to have amorphous structure due to low curing temperature.Thicknesses of the prepared films were measured to be generally in 80–90nm range.Only the film,which was prepared from the sol havingbimodalFig.1.FT-IR spectra of sol (a)as prepared,(b)after 20h duration.Table 2Variation of SiO 2particle size with respect to HNO 3/TEOS and H 2O/TEOS ratios.HNO 3/TEOS/H 2O/TEOS 4.74×10−3 4.74×10−4 4.74×10−5 4.74×10−6 4.74×10−77.809±2.0nm%80:20±2.0nm/%20:300±5.0nm 9.0830±2.1nm 10.3317±1.5nm12.95GelationGelation41±3.0nm40±1.5nm1516±2.5nm 18.1113±2.6nmGelationFig.2.Particle size distribution plots of representative systems.3132Ö.Kesmez et al./Journal of Non-Crystalline Solids 357(2011)3130–3135particle size distribution,had about 120nm of thickness.This behavior was observed in previous studies [7].Sols having larger particles result in thicker films as compared to sols having smaller particles,on the condition that the withdrawal speed is kept constant [7].Pencil hardnesses of the films were in 6H –9H range,as presented in Table 3.These results indicate that the hardnesses of the films were quite high and that the films can withstand mechanical environmen-tal effects.In addition,the films did not peel off or only slightly peeled off in adhesion tests.Along with these results,adhesion of the films was classi fied as 5B or 4B according to ASTM D 3359standard.Light transmittance increase values of the films are presented in Table 3.SiO 2films provided a light transmittance increase in the range of 4.6–5.6%.Light transmittance of the sample prepared after 45days aging of AR10sol was measured in order to investigate the effect of aging duration on transmittance.It was seen that the film provided 5.2±0.2%increase in transmittance,as compared to bare glass substrate.Before aging,transmittance increase was 5.6±0.2%.This result can be expected since particle size distribution of the sol did not present a major change with aging duration,as shown in Fig.3.Average particle size of SiO 2increased to 34±0.6nm from 30±2.1nm after 45days of aging.It was seen in SEM examinations that the formed AR films were crack free and they had a uniform structure.SEM micrograph of AR10sample is presented in Fig.4.SiO 2particles can be discerned in this high magni fication micrograph.Size of SiO 2particles observed in SEM micrographs was seen to be in accord with the results of particle size measurements performed from SiO 2sols.AFM image of AR10is presented in Fig.5.Uniform structure of the films was veri fied by AFM analyses (Fig.5inset).RMS roughness of the AR10film was determined as 0.8nm.Diffuse re flectance analysis (DRA)results presented in Fig.6indicate the anti-re flective character of the obtained films.DRA analyses are generally in accord with the %increase in transmittance results of the samples given in Table 3,which were measured at 550nm with a hazemeter.The re flectance of the uncoated sample is seen to be quite high (about 10–11%)as compared to the coated samples.The coated samples have a re flectance of 6–7%at 400nm,which is seen to decrease to 4.3–5.5%at 550–600nm,indicating the antire flective property provided by the coatings.The lowest re flec-tance is obtained by the sample AR10,with a re flectance of about 4.3±0.1%at 550nm.These results point out that coatings obtained with one step acid catalysis provide about 6%increase in transmittance of the glass in the visible region,which was also veri fied by transmittance measurements.4.DiscussionSiO 2particle size was seen to increase when H 2O/TEOS ratio was increased from 7.80to 10.33,keeping the HNO 3/TEOS ratio constant at 4.74×10−3.Growth of SiO 2particles with increase in H 2O amount can be suggested to be a result of increase in hydrolysis and condensation rates.When the H 2O/TEOS ratio was further increased to 18.11,particle size decreased.The decrease in the particle size may be attributed to the hydrolytic depolymerization reaction,which is the reverse reaction of condensation,as a result of increase in the excess H 2O amount in the system [28].Gelation occurred when HNO 3/TEOS ratios of 4.74×10−4M and 4.74×10−5were utilized at H 2O/TEOS ratio of 12.95.When acid ratios of 4.74×10−6and 4.74×10−7were employed,formation of the SiO 2particles may be attributed to the decrease in the condensation rate as a result of decreasing HNO 3ratio.High rate of the reaction which leads to gelation decreases,providing the formation of SiO 2particles [28].Increase in the particle size can be expected when lower acid ratios were utilized (4.74×10−6or 4.74×10−7)since lower acid ratio results in initiation of polymerization from fewer points,leading to larger particle size,as compared to high acid ratio (4.74×10−4).RateFig.3.Particle size distribution plots of SiO 2sols (AR10system)when prepared and after 45days of aging.Table 3SiO 2average particle size in the sols,thicknesses and pencil hardnesses of the prepared films and %T increases provided by the films.Sample No Particle size (nm)Film thickness (nm)%T increase (%points)Pencil hardness and adhesion test results AR117±1.584.3±5.14.6±0.1N 9H/5B AR2***AR3***AR441±3.089.5±3.0 5.0±0.27H/4B AR516±2.591.7±1.4 4.6±0.19H/5B AR613±2.688.2±0.8 4.6±0.19H/4B AR740±1.580.9±2.2 5.0±0.27H/4B AR8%80:20±2.0%20:300±5.0122.6±5.2 4.8±0.16H/3B AR9***AR1030±2.1(34±0.6+)89.0±2.6 5.6±0.2(5.2±0.2+)8H/4B AR119±2.075.5±1.34.7±0.19H/4B*Gel formation occurred during synthesis.+Measured after 45days.Fig.4.SEM micrograph of AR10sample.3133Ö.Kesmez et al./Journal of Non-Crystalline Solids 357(2011)3130–3135of hydrolysis and condensation reactions of silicon alkoxides was suggested to be altered by utilizing acid catalysts [15,28].Pope and Mackenzie reported that variations on porosity,shrinkage and gelation duration can be obtained by altering the catalyst in hydrolysis and condensation of TEOS [29].Gelation time was found to decreaseto almost one-tenth of non-catalyzed system,when 5×10−2M HCl was added to TEOS-ethanol mixture [5].The ratio of H 2O to EtOH may also be signi ficant.EtOH,which was used as the solvent in the prepared sols,forms hydrogen bonds with H 2O molecules.This may reduce the available free H 2O which is required for the hydrolysis of TEOS.Ratio of H 2O to EtOH is presented in Table 1.It was seen that when this ratio falls below 1,abnormal particle size distribution is obtained such as bimodal distribution (Sample AR8)and 9nm average particle size (Sample AR11).These results indicate that it is possible to control the SiO 2particle size by altering the H 2O and HNO 3ratios.However,the growth behavior of SiO 2particles is complex and shows alterations with respect to changes in H 2O/TEOS and HNO 3/TEOS parameters.Indeed,as proposed by Hench and West [18],numerous factors affect hydrolysis and condensation rates,and the course of events is more complex than just simple hydrolysis and condensation reactions.Additionally,hydrolysis and condensation takes place simultaneously.As it was reported in the previous section,acid-water ratio has an in fluence on the size of the SiO 2particles.Size of the SiO 2particles varied in the range of 9–40nm as a result of the change in the acid –water ratio.However,light transmittance results reveal that the change in the SiO 2particle size in this range only slightly affects the antire flective property of the film.Therefore,acid –water ratio in the sols has a slight in fluence on the light transmittance of the obtained films.Increase in the transmittance provided by the films can be correlated with the average size of SiO 2particles in films.Sols and obtained films from these solscanFig.5.AFM figure of sampleAR10.Fig.6.Diffuse re flectance plots of bare glass and coated glass samples.3134Ö.Kesmez et al./Journal of Non-Crystalline Solids 357(2011)3130–3135be divided into3groups as a function of particle size and%T increase.In thefirst group,light transmittance increase is between4.6and4.8±0.1%, while the sols have average SiO2particle size of b20nm.On the other hand in the second group,thefilms obtained from sols with particle size of about40nm provided transmittance increase of5±0.2%.Sol having average SiO2particle size between20and30nm(sample AR10)was seen to increase transmittance5.6±0.2%.It can be inferred from these results that the pore size and volume ratio of pores in AR10film are more appropriate for reducing reflective losses than the other investigated systems.It was seen during high magnification SEM investigations that the SiO2particles on thefilms formed cluster-like structures,among which there were gaps.These gaps,which can be seen as black,curved lines in Fig.4are not cracks,since cracks infilms follow a straight path with brittle nature.The gaps are believed to form from clustering of the SiO2particles most probably during drying and baking of thefilms, as a result of densification and shrinkage.Nevertheless,as can be inferred from the cross-cutter test and pencil hardness test results, mechanical properties of thefilms are quite good and they appear not to be deteriorated by the presence of these gaps.5.ConclusionEffects of HNO3and water amount on size of SiO2nano-particles in sols and on light transmittance of the obtainedfilms from these sols have been investigated.SiO2particle sizefirst increased and then decreased with increasing H2O ratio,when4.74×10−3HNO3/TEOS ratio was used.The decrease in the particle size with increasing H2O/ TEOS ratio was attributed to the hydrolytic depolymerization reaction, which is the reverse reaction of condensation.Control of the SiO2 particle size was seen to be possible by altering the H2O/TEOS and HNO3/TEOS ratios,although SiO2particle growth behavior is complex and show alterations with respect to changes in H2O and HNO3ratios. Obtainedfilms are generally80–90nm in thickness and they have high hardness and high adherence to the glass substrate.A light transmit-tance increase of5.6±0.2%was provided by thefilm which had an average SiO2particle size of30±2.1nm.Particle size distribution of this sol presented a slight change in45days(34±0.6nm),indicating that the sols were stable for long durations and that they had long shelf life.Thefilm obtained from45day aged sol provided a light transmittance increase of5.2±0.2%.AcknowledgementsAuthors thank Akdeniz University Research Fund forfinancial support.Technical andfinancial support of NANOen and Mattek is gratefully acknowledged.Help of Prof.Dr.TayfurÖztürk(METE/METU) for FESEM analyses is acknowledged.References[1]S.Lien,D.Wuu,W.Yeh,J.Liu,Sol.Energ.Mat.Sol C90(2006)2710–2719.[2]K.Abe,Y.Sanada,T.Morimoto,J Sol-Gel Sci Technol22(2001)151–166.[3]Lin J-H(Zuel),US Patent6929861,16August2005.[4] C.Schelle,M.Mennig,H.Krug,G.Jonschker,H.Schmidt,Journal of Non-CrystallineSolids218(1997)163–168.[5] C.J.Brinker,G.W.Scherer,Sol-Gel Science,,Academic Press,San Diego,1990.[6] B.G.Prevo,Y.Hwang,O.D.Velev,Chem Mater17(2005)3642–3651.[7]Ö.Kesmez,N.Kiraz,E.Burunkaya,H.E.Çamurlu,M.Asiltürk,E.Arpaç,J Sol-Gel SciTechnol(2010),doi:10.1007/s10971-010-2290-x.[8]Ö.Kesmez,H.E.Çamurlu,E.Burunkaya,E.Arpaç,Ceram Int.36(2010)391–394.[9]Ö.Kesmez,H.E.Çamurlu, E.Burunkaya, E.Arpaç,Sol Energ Mat93(2009)1833–1839.[10] E.Burunkaya,Ö.Kesmez,N.Kiraz,H.E.Çamurlu,M.Asiltürk,E.Arpaç,Mater ChemPhys120(2010)272–276.[11]K.Koc, F.Z.Tepehan,G.G.Tepehan,Journaşof materials scince40(2005)1363–1366.[12]G.R.Fowles,Introduction to Modern Optics,Dover Publications,New York,1989.[13] D.Chen,Sol Energ Mat Sol C68(2001)313–336.[14]P.Nostell,A.Ross,B.Karlsson,Thin Solid Films351(1999)170–175.[15]M.A.Fardad,J Mater Sci35(2000)1835–1841.[16]I.V.Kityk,J.Ebothe,Q.Liu,Z.Sun,J.Fang,Nanotechnology17(2006)1871–1877.[17]H-S Tong,C-M Hu,US Patent5582859,10December1996.[18]L.L.Hench,J.K.West,Chem.Rev90(1990)33–72.[19]H.Schmidt,H.Scholze,A.Kaiser,Journal of Non-Crystalline Solids63(1984)1–11.[20]BE(Churchill)Yoldas,DP(Wilkinsburg)Partlow,US Patent4535026,13August1985.[21]I.A.Rahman,M.Jafarzadeh,C.S.Sipaut,Ceram Int35(2009)1883–1888.[22] C.J.Brinker,K.D.Keefer,D.W.Schaefer,R.A.Assink,B.D.Kay,C.S.Ashley,J Non-Cryst Solids63(1984)45–59.[23] A.S.Dorcheh,M.H.Abbasi,J Mater Process Tech199(2008)10–26.[24] A.Vincent,S.Babu,E.Brinley,A.Karakoti,S.Deshpande,S.Seal,J Phys Chem C111(2007)8291–8298.[25]New Test Method for Optical Imaging Evaluation of Adhesion by Tape TestSpecimens,ASTM D3359WK97.[26]G.Wu,J.Wang,J.Shen,T.Yang,Q.Zhang,B.Zhou,Z.Deng,B.Fan,D.Zhou,F.Zhang,Mater Sci Eng B78(2000)135–139.[27] F.Rubio,J.Rubio,J.L.Oteo,Spectrosc Lett31(1998)199–219.[28] C.J.Brinker,J Non-Cryst Solids100(1988)31–50.[29] E.J.A.Pope,J.D.Mackenzie,J Non-Cryst Solids87(1986)185–198.[30]S.Tabatabaei,A.Shukohfar,R.Aghababazadeh,A.Mirhabibi,J.Phys.Conf.Ser.26(2006)371–374.3135Ö.Kesmez et al./Journal of Non-Crystalline Solids357(2011)3130–3135。