Polyvinylbutyral Based Hybrid Organic/Inorganic Films as a MoistureBarrier MaterialSatyajit Gupta,†,‡ Sindhu Seethamraju,‡ Praveen Chandrashekarapura Ramamurthy,*,†,‡

and Giridhar Madras‡

†Department of Materials Engineering, Indian Institute of Science, Bangalore, India‡Center for Nanoscience and Engineering, Indian Institute of Science, Bangalore, India

*S Supporting Information

ABSTRACT: Flexible and thermally stable, freestanding hybrid organic/inorganic based polymer-composite films have beenfabricated using a simple solution casting method. Polyvinylbutyral and amine functionalized mesoporous silica were used tosynthesize the composite. An additional polyol“tripentaerythritol”component was also used to increase the −OH groupcontent in the composite matrix. The moisture permeability of the composites was investigated by following a calciumdegradation test protocol. This showed a reduction in the moisture permeability with the increase in functionalized silica loadingsin the matrix. A reduction in permeability was observed for the composites as compared to the neat polymer film. The thermaland mechanical properties of these composites were also investigated by various techniques like thermogravimetric analysis,differential scanning calorimetry, tensile experiments, and dynamic mechanical analysis. It was observed that these propertiesdetoriate with the increase in the functionalized silica content and hence an optimized loading is required in order to retaincritical properties. This deterioration is due to the aggregation of the fillers in the matrix. Furthermore, the films were used toencapsulate P3HT (poly 3 hexyl thiophene) based organic Schottky structured diodes, and the diode characteristics underaccelerated aging conditions were studied. The weathered diodes, encapsulated with composite film showed an improvement inthe lifetime as compared to neat polymer film. The initial investigation of these films suggests that they can be used as a moisturebarrier layer for organic electronics encapsulation application.

■ INTRODUCTION

Moisture and gas barrier materials have versatile applications ina broad range of areas. Barrier materials are critical in food/beverage and electronics packaging industries. Organicconducting polymer based devices like organic photovoltaicsand organic field effect transistors are extensively studied1−3

because of their flexibility, light weight, and cost effectiveness.However, commercialization of these devices is hampered bythe instability of the devices toward moisture and oxygen.4−8

The active device components such as the electrode materialand the organic conducting polymer are highly susceptibletoward degradation due to oxygen and moisture. Therefore, asuitable encapsulant material is required to protect thesedevices and provide a lifetime of ≥10 years. This requires thatthe encapsulant has a water vapor transmission rate (WVTR)that should be no more than 10−6 g m−2 day−1 and an oxygentransmission rate (OTR) that should be no more than 10−3 cm3

m−2 day−1.9,10 Hence, development of a barrier material ishighly important for both organic and inorganic electronicdevices.Polymer based composite materials find a variety of uses

ranging from transportation, marine industries, packaging, andspace vehicles. The polymer based composite materials whichpossess mechanical flexibility, good barrier properties, andthermal stability can be used for the encapsulation of electronicdevices. Polymer nanocomposite materials based on siliconepolymers have been developed which can be used forencapsulation of organic devices.11−14 In the above studies,surface amine/allyl modified alumina nanoparticles and allyl

functionalized mesoporous silica particles were used as the fillermaterial for various silicone resins. Epoxy and hydrideterminated silicone resins were used as a polymer matrix, andthe composites were fabricated by in situ thermal curingtechnique. Two diverse routes, amine-epoxy curing11 andhydrosilylation reaction12,13 strategies were followed to obtain acomposite matrix for the potential application in organicdevices. Inorganic oxide nanoparticles (like Al2O3) can be usedas filler in the polymer matrix to reduce the gas permeability.15

The present work is focused on the fabrication andcharacterization of a polymer composite based matrix, as amoisture barrier material. Polyvinylbutyral was chosen as thepolymer matrix, which is a good ceramic binder and widelyused in the automotive industries.16 It is commonly used as acomponent in laminated safety glass and in photovoltaic solarpanels. This polymer matrix, having excellent film formingability, provides good adhesion to various surfaces.17 Othercritical properties of the PVB polymer include optical clarity,toughness, flexibility, resilience, and high impact strength at lowtemperatures.Amine functionalized mesoporous silica (prepared through

silane coupling methodology) was used as a reinforcing fillermatrix for the hybrid composite. Mesoporous silica serves as agood filler,18 because of the confinement of the polymer chains

Received: August 21, 2012Revised: February 17, 2013Accepted: March 1, 2013Published: March 1, 2013

Article

pubs.acs.org/IECR

© 2013 American Chemical Society 4383 dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−4394

in the mesopores of silica particles. It also provides a torturouspathway for the incoming molecules and thus reduces thepermeability.19 In addition, surface amine groups can also formhydrogen bonds with −OH groups in the polymer matrix(PVB) and enhance the interfacial interaction that wouldprovide good thermal and mechanical stability. Along withmesoporous silica, a polyol“tripentaerythritol” was alsoused for the composite matrix, which provides multiple polar−OH sites in the composite matrix. This can further reduce thepermeability of moisture through hydrogen bonding (polar−polar interaction)20 and hence acts as a trap for moisture. Incomparison to the existent organic/inorganic multilayeredencapsulation (VITEX)9/ALD (atomic layer deposition)/MLD(molecular layer deposition) based methods of encapsulation,this method of encapsulation is simple, faster, and less energyintensive but needs further optimization to achieve lowerWVTR values.The objective of this study was to synthesize functionalized

silica based PVB composite to be used as a moisture barriermaterial for the encapsulation of organic Schottky structureddevices. The general studies on the composites were carried outto evaluate the thermo-mechanical characteristics of thecomposites. The optimum loading of the silica particles thatcan be used for the application as an encapsulant for organicdevices was discussed. The effect of loading of functionalizedsilica in the hybrid composite materials was evaluated bythermo-mechanical and light absorbance techniques. Inaddition, the moisture permeability of the composites wasdetermined by the calcium degradation test.21 The compositeswere used to encapsulate diode devices, and the deviceproperties under accelerated aging conditions were studied.

■ EXPERIMENTAL SECTION

Materials. Aminopropyltrimethoxysilane (APTMS), tripen-taerythritol, Butvar B-98 polymer matrix (having hydroxylcontent about 18−20%, which is expressed as percent polyvinylalcohol, acetate content of 0−2.5%, expressed as percentpolyvinyl acetate, and butyral content of ∼80%, expressed aspercent polyvinyl butyral) of molecular weight about 40 000−70 000 g mol−1 and mesoporous silica [MSU-H, large pore 2D(pore volume 0.91 cm3 g−1 and pore size ∼7.1 nm) hexagonal,d = 2.6 g cm3 as specified by the manufacturer] were obtainedfrom Sigma-Aldrich Company Ltd. (St. Louis, MO) USA.Reagent grade toluene was obtained from local suppliers (SDFine Chem), which was distilled over pressed sodium andpreserved under an inert atmosphere before use. Absoluteethanol (purity ≥99.9%) was obtained from local suppliers(SD. Fine Chem) and was used as a solvent for the compositepreparation without further purification.

■ COMPOSITE FABRICATION

Step I: Synthesis of Amine Functionalized Silica. Inorder to modify the mesoporous silica surface, the particleswere dried at 120 °C for 10 h. Then, the surfacefunctionalization was carried out under dry toluene reflux(Scheme 1A).11,12 The mesoporous silica particles weredispersed in dry toluene for 30 min by sonication, ATPMSwas added to the mixture and refluxed under inert atmospherefor 20 h. These treated particles were separated usingcentrifugation; thoroughly washed multiple times using tolueneto remove the unreacted siloxanes; and then dried undervacuum (25 mm Hg) for 8 h at ∼100 °C to remove any

residual toluene. These dried functionalized silica powders wereused for further characterization and composite fabrication.

Step II: Composite Film Fabrication: Solution Casting.The composite fabrication was carried out by the solutioncasting method. A 5 g portion of PVB polymer (powderformstructure given in Scheme 1C) was added in 70 mL ofethanol (14 mL g−1), dissolved by stirring at 50 °C for 45 min.To the mixture, 0.01 g of the polyol (i.e., 5.37 μmol g−1 withrespect to the PVB content and this amount was held constantfor all the composites) was added and stirred at 60 °C for 2 h.Thereafter, various weight percentages (0.25, 0.5, and 1.5) offunctionalized silica particles (with respect to the polymermatrix and were dried prior to the use) were added, stirred for15 min, and sonicated for 30 min to assist in dispersion at roomtemperature (25 °C). The homogeneous solution was trans-ferred into a Teflon coated mold, dried at 40 °C in ambientatmosphere to obtain transparent films and further dried undervacuum. As a control, a neat polymer film was prepared byfollowing the same procedure described above, by dissolvingPVB in ethanol at 50 °C and then casted. The films were thenpulled out from the cast (average thickness ∼250 μm) and usedfor further studies. The pristine polymer, 0.25, 0.5, and 1.5 wt %of functionalized silica loading in the polymer are designated asPV0, PV1, PV2, and PV3.

■ CHARACTERIZATIONPerkin-Elmer (Spectrum GX) spectrometer was used to recordthe FTIR (Fourier transform infrared spectroscopy) spectra ofboth pristine and functionalized silica particles. The spectra

Scheme 1. (A) Pristine Silica Functionalization. (B)Composite Hybrid Matrix, Showing the Mechanism withWhich It Can Reduce the Permeability. (C) Schematic of thePolymer (PVB) Backbone Structure

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944384

were recorded using potassium bromide (KBr) pellet methodfor both samples in the range 400 to 4000 cm−1 with a spectralresolution of 4 cm−1. Raman spectra were collected using NXRFT-Raman Module (ThermoScientific). Solid-state 29Si (onepulse experiment) and 13C CPMAS (cross-polarization magicangle spinning) for both pristine silica and functionalized silicawere recorded on a 300 MHz Bruker DSX. In the case of 29Si,the relaxation delay was 12 s. In 13C, the spinning rate was 7kHz, the contact time was 1200 μs, relaxation delay was 5 s, anddecoupling sequence spinal 64 was used. The surface area ofpristine and functionalized silica was measured by theBrunauer−Emmett−Teller (BET) nitrogen sorption methodat 77 K with a Belsorp instrument from Japan. For the nitrogenadsorption/desorption experiments, samples were degassed at130 °C for 6 h. The quantification of APTMS was carried outby elemental (CHN) analysis and thermogravimetric analysis(TGA). The TGA (Perkin-Elmer) analysis was carried out inorder to evaluate the surface functionalization as well as thethermal stability of the composites, at a heating rate of 10 °Cmin−1. A Perkin-Elmer 2400 Series II CHNS/O system wasused for elemental (CHN) analysis.In order to monitor the thermal history of the composites as

well as the pristine polymer, a differential scanning calorimetry(DSC) technique was carried out on a Mettler Toledo (DSC822e) instrument. Analysis was carried out in argon atmosphereat a flow rate of 80 mL min−1 in a hermitic aluminum pan atheating rates of 10 °C min−1 (the DSC instrument wascalibrated using standard indium and zinc specimens). Thetensile studies for PVB/functionalized silica composite wereperformed using Zwick/Roell instrument by 0.15 mm s−1 astest speed and average value is reported. ASTM D638 was usedas a standard for the tensile studies. The morphologies of thecross-sectional surface of the fractured surfaces (after tensileexperiment) of the pure polymer and the composites wereobserved in field emission scanning electron microscope(FESEM), in Sirion. In case of pristine silica, powder samplewas directly coated over carbon tape and morphology wasobserved using scanning electron microscopy (SEM), whichwas carried out using ESEM Quanta. Prior to the SEM analysis,samples were sputter-coated with thin film of gold using JEOL(JFC-1100E) ion sputtering device. JEOL 2000 FX-II TEM(transmission electron microscope) was used to observe thesize and morphology of the silica at an accelerating voltage of200 kV. The specimen was dispersed in ethanol andultrasonicated and drop casted on a copper grid with acarbon-reinforced plastic film and then dried. UV−visiblespectra of the pristine polymer and composite films wereobtained in Hitachi U 3000 in a wavelength, ranging from 200to 1050 nm. Optical microscopy of the composites was taken intransmittance mode in Axiovert 200 MAT inverted microscope.Dynamic mechanical analysis (DMA) of the composites werecarried out in MetraVib DMA+100, in tensile mode at aconstant frequency of 1 Hz, in a temperature range from 50 to100 °C. A static force of 0.5 Newton and dynamic force of 2Newton was applied on the samples. The static contact anglemeasurement of the PVB composite films were carried out at25 °C, in an OCA 30 goniometer (Dataphysics, Germany)containing stepper motor for controlling the volume (3 μL) ofthe liquid (Millipore water) supplied from a microsyringe. Fivereadings were taken for each sample in different positions. Aprogrammable humidity chamber (Kaleidoscope, India, ModelNumber-KEW/PHC-80) was used for weathering study.

Calcium Degradation Test. The moisture permeabilitywas measured by the calcium degradation test. A calcium square(1 cm × 1 cm) of 150 nm thickness (which acts as a moisturesensor) was deposited over a cleaned glass slide using a shadowmask, inside a glovebox (MBRAUN, MB 200B, ultra high pureargon atmosphere, H2O < 10 ppm, O2 < 10 ppm), connectedwith a thermal evaporator (Sigma Instruments), under highvacuum of ∼10−6 mbar. Then aluminum, which acts as anelectrode, was deposited (200 nm) on the top of the asdeposited calcium layer through a shadow mask. Then thecalcium/aluminum deposited glass substrate was covered withthe composite films (of same thickness and prepared undersimilar conditions as discussed previously) and the sides weresealed with a glue (room temperature curing epoxy glue-LapoxL12) to stop the leakage through sides (an image of the setup isgiven in Figure S1see the Supporting Information). To verifythe permeability through the glue, a control experiment wascarried out by sealing a glass substrate, with the same glueunder similar conditions as maintained for the sealing of thecomposites.The encapsulated glass slides were inserted in a program-

mable humidity chamber (RH = 95% and T = 35 °C,Kaleidoscope, India), and the resistance values were measuredover time. The change in resistance (R), due to the degradationof the calcium is inversely proportional to the height of theremaining calcium layer (H).21

∝R H(1/ ) (1)

The permeation rate of moisture (P) through the compositefilm is proportional to the slope of 1/R (conductance) over themeasured period (T). This can be expressed as21

δρ= −P nM

MLB

RT

d(1/ )d

(H2O)

(Ca) (2)

where n is molar equivalence for the reaction between waterand calcium, M(H2O) is the molecular weight of water, and M(Ca)is the molar mass of calcium, δ is the density, and ρ is theresistivity of calcium. L and B are the length and width of the asdeposited calcium. In this study, we have used the same valuefor both L and B.The swelling studies of the composites were carried out in

deionized (DI) water (∼5 mL) at 25 °C. The composite filmswere cut into 8 mm × 8 mm (l × w) and were dipped in DIwater for 36 h. The solvent (water) attached to the surface wasremoved using tissue paper, and the weight change wasmeasured using an analytical microbalance (Essae TeraokaLimited with a resolution of 0.01 mg).

Organic Device Encapsulation and Weathering Study.An organic device fabrication was carried out inside a glovebox.One weight percent of poly(3-hexylthiophene) (P3HT)(P3HT was synthesized in a previously reported method)22,23

was dissolved in chlorobenzene by stirring for 12 h, under inertatmosphere. Then, the solution was filtered using a 0.45 μmNylon filter to remove agglomerates. The filtrate was used fordevice fabrication. At first 25.4 mm × 25.4 mm indium tinoxide (ITO) coated glass slides, obtained from DeltaTechnologies, Limited, USA, were pretreated with concentratedHCl to remove the ITO from the sides using a mask at thecenter. The ITO layer area in the middle of the slides becomes15 mm × 25.4 mm. Then these ITO coated glass slides werecleaned using isopropanol and acetone, and then, they were

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944385

subjected to RCA1 solution (5:1:1 of H2O:H2O2:NH4OH).Finally they were rinsed with water and dried with dry argon.A solution (150 μL) of P3HT in chlorobenzene was spin

coated (1000 rpm speed for 10 s) on a cleaned ITO coatedglass slide. Then it was annealed at 120 °C for 10 min. Thenaluminum (contact area of 4 mm2) electrodes were depositedover P3HT layer using a shadow mask (Figure S2, see theSupporting Information) by thermal evaporation inside aglovebox. Devices were encapsulated using the composite filmas well as neat polymer film. The glue used for encapsulationwas Lapox L12, which is the same glue as used for calcium test.The current−voltage (I−V) characteristics of the fabricateddevices were measured using a source meter (Keithley, Model2420). The accelerated aging of the devices were carried outinside a humidity chamber (Figure 2).

■ RESULTS AND DISCUSSION

Fabrication of the Composite Films. In the presentwork, solution casted PVB film as well as PVB/aminefunctionalized silica based hybrid composite films werefabricated using ethanol as solvent. The amine functionalizedsilica particles were used for the reinforcement of the polymermatrix. The functionalization of mesoporous silica was carriedout using aminopropyltrimethoxysilane as a coupling agent. Inaddition to functionalized silica particles, a polyoltripentaer-ythritolwas used for the composite matrix fabrication. Hence,it is envisioned that the synergistic effect (Scheme 1B) of theinorganic phase−silica particles and polyol, employed tofabricate the composite matrix, that can reduce the permeabilityof the water vapor.

■ PART I: CHARACTERIZATION OF AMINEFUNCTIONALIZED SILICA

FTIR and Solid State NMR: 13C MAS NMR and 29SiNMR. The FTIR spectra of pristine and amine functionalizedsilica particles (Figure 1A and B) were carried out in order tovalidate the functionalization at the silica surface. In the spectra,a few new peaks were observed after functionalization whichwere absent in the pristine silica, which is due to the grafting ofsiloxane molecules onto the surface of the nanoparticles. In theFTIR (Figure 1A) spectra of pristine silica, the broad peak at3436 cm−1 is due to the presence of −OH groups at the silicaparticle surface and peak at 1637 cm−1 is due to bending of−OH groups. After functionalization (Figure 1B), the peakobserved at 2937 cm−1 is characteristic of asymmetric −CH2stretching vibrations and at 1494 cm−1 is due to −CH2 bending(scissoring). The peak appearing at 1562 cm−1 is due to N−Hbending (scissoring) vibrations. The Raman study (Figure S3see the Supporting Information) also shows a peak around2900 cm−1, characteristic of the aliphatic domain (C−H). Thesiloxane grafting was further analyzed by solid state NMR.Figure 2A shows the solid-state 29Si spectra of pristine

mesoporous silica, which shows three signals at −100 (Q2-geminal silanols), −109.7 (Q3-free silanols), and −114.9 (Q4-siloxane groups) ppm.13 After functionalization, new peakswere observed (Figure 2B) in the range from −50 to −80 ppmindicating that the silica surface is chemically modified.24 Forthe functionalized silica, the peaks appearing at −58.5 (T2-bidentrate) and −67.3 (T3-tridentrate) ppm can be assigned tothe chemical grafting of the organic ligand in two differentmodes24 of the siloxane−APTMS.

In addition to solid state 29 Si NMR, 13C NMR was alsocarried out. Figure 2C shows a peak around 10.8 ppm, which isascribed to the carbon atom directly bonded to silicon (−Si−CH2−). The peak at around 24.5 ppm corresponds tomethylene carbon where as the peak observed around 44.8ppm is due to the methylene group carbon atoms (−CH2−NH2) attached to the amine group. These results of solid state29 Si NMR and 13C NMR indicate the grafting of APTMS at thesurface25 and support the results obtained from FTIR.

BET Isotherm Analysis. BET analysis shows a decrease inthe Vm [the monolayer adsorption amountcm3 (STP) g−1],pore volume, C constant26 (related to the enthalpy ofadsorption and a dimensionless quantity; the decrease in theC constant indicates a decrease in the interaction betweenadsorbate nitrogen molecules and the particle surface), and thesurface area reduced by ∼84% after functionalization, which isdue to the attachment of the APTMS at the surface. All theparameters obtained from BET analysis are as shown in Table1. The adsorption/desorption isotherm (Figure 3A) resemblestype IV and has an H2 type of loop due to the mesoporousnature of the particles as per IUPAC classification.27 Afterfunctionalization, the mesoporosity is retained, as observed inthe BET adsorption/desorption curve for the functionalizedsilica. It can be also observed that the shape of hysteresis loopsbefore and after functionalization are almost similar,13 whichshows that the pore shape may not be significantly changedafter siloxane functionalization. The morphology of themesoporous silica (SEM image) and the TEM images of usedsilica are as shown in Figure 3B and C.

Figure 1. FTIR spectra of (A) pristine and (B) functionalized silica.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944386

Quantification of Surface Grafting: TGA and Elemen-tal (C, H, and N) Analysis. Thermogravimetric analysis(Supporting Information Figure S4) of pristine and function-alized silica was used further to calculate the extent of graftingat the surface. Pristine silica shows some weight loss in theregion of 40−125 °C, due to loss of adsorbed moisture. Thehuge weight loss of functionalized silica as compared to pristinesilica of ∼17.2% in the region 125−730 °C is due to thedegradation of the organic fragment. Surface APTMS groupswere calculated to be 4.39 ± 0.3 μmol m−2, using the followingequation28

Figure 2. (A) 29Si NMR of pristine silica, (B) 29Si NMR of functionalized silica, and (C) 13C NMR spectra of functionalized silica.

Table 1. Various Parameters Obtained from the BET SurfaceArea Analyzer and CHN Analysis Experiments

parameterspristinesilica

functionalizedsilica

surface area (aBET) [m2 g−1] 679.6 111.4

total pore volume (P/Po = 0.99) [cm3 g−1] 0.9982 0.2894Vm [cm3 (STP) g−1] 156.2 25.6C 124.8 33.4mean pore diameter [nm] 5.87 10.39carbon (%) from CHN analysis 0.38 12.20hydrogen (%) from CHN analysis 1.42 3.09nitrogen (%) from CHN analysis 4.43

Figure 3. (A) Adsorption/desorption isotherm of the pristine and functionalized silica, (B) SEM image of the neat silica, and (C) TEM image ofneat silica before functionalization.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944387

= ×Q W M S/( )TGATGA OF silica (3)

In the above equation, QTGA is the grafting density inmicromoles per squared meter, WTGA is the weight loss(∼17.2%) obtained from TGA in the specified temperaturerange, MOF is the molecular weight of corresponding organicfragment, and Ssilica is the specific surface area of the usedmesoporous silica (679 m2 g−1obtained from BET).Elemental (CHN) analysis indicates an increase in the

carbon content (Table 1) as well as appearance of nitrogencontent after functionalization. Carbon content as detected inpristine silica could be due to the adsorbed CO2. From CHNanalysis, the grafting APTMS density was found to be 4.8 μmolm−2 by using the following equation28

δ= × ×Q M N SC/( )CHNC C silica (4)

Where QCHN is the grafting density in micromoles per squaredmeter, δC is the increase in carbon content (%), afterfunctionalization, as observed (Table 1) from elemental(CHN) analysis. MC is the atomic weight of carbon, NC isthe number of carbon atoms, and Ssilica is the specific surfacearea of used mesoporous silica (679 m2 g−1obtained fromBET).The estimation from elemental (CHN) analysis (4.8 μmol

m−2) shows a similar value obtained from TGA analysis (4.39 ±0.3 μmol m−2), which are normalized with respect to surfacearea obtained from BET.

■ PART II: COMPOSITE CHARACTERIZATION

Tensile Studies of PVB−Amine Functionalized Silica/PVB Composites and Fractured Surface SEM. The stress/strain curves for neat polymer and the composites are as shownin the Figure 4, and the obtained Young’s modulus, yield stress,and the percent elongation at break values are tabulated inTable 2 (the tensile experiments were carried out at 25 °C). Itis observed, that the yield stress increased from 22.5 to 44 MPa,for PV0 to PV3, which shows an increase of 2 times the yieldstress value with respect to PV0. For PV1 and PV2, the increasein yield stress is in the range of 1.2 and 1.4 times, respectively,as compared to PV0. There exists an effective interaction andintegrity between amine functionalized silica and the PVBmatrix, and it transmits the tensile load effectively. It can be alsoobserved that Young’s modulus increased from neat PVB(PV0) to PV3. The modulus values for PV1, PV2, and PV3 arealmost similar showing that the materials are stiffened with thesilica particle addition within the proportional limits.16 Thepercent elongation at break was 0.11 for PV0 and 0.94 for PV2.In comparison, PV1 and PV2, the decreasing strain percentvalue may be due to the brittleness of the PVB matrix upon theaddition of excess silica particles due to agglomeration. This isalso evident from the existence of plateaus, observed in PV3(Figure 4) which is due to the possibility of slippage byfunctionalized silica fillers upon higher loadings in thecomposite matrix. The “agglomeration/cluster” effect in PV3

Figure 4. Stress/strain curves of the polymer and the composites.

Table 2. Mechanical, Thermal Properties and Contact Angle Values for PVB, Amine Functionalized SilicaPVB Composites

sample Young’s modulus (MPa) yield stress (MPa) (avg) elongation at break (%) (avg) degradation temperature (°C) −10% contact angle (deg)

PV0 6 ± 1 22.5 ± 1 11 ± 2 362 87 ± 1PV1 11 ± 2 27.0 ± 1 61 ± 1 360 85 ± 0.5PV2 9 ± 1 32.5 ± 3 94 ± 3 362 83.6 ± 0.3PV3 10 ± 1 44.0 ± 2 30 ± 2 356 82 ± 0.3

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944388

could be possible due to hydrogen bonding between thefunctionalized silica particles, containing unreacted −OH andsurface decorated −NH2 groups as the number densityincreases inside the matrix (See the Supporting Information,Figure S5).The fractured surface (obtained from the tensile testing)

images show (Figure 5) more cracks and cleavages in thecomposites compared to polymer, which could be due to theincreased interfacial interaction between amine functionalizedmesoporous silica and the polymer matrix. Thus the mechanicalproperties of the composites increased from PV0 to PV1 toPV2 but decreases for PV3 due to agglomeration as evidencedfrom the fractured surface image (Figure 5, PV3 (inset)). Inorder to verify the homogeneity of the functionalized silica inthe composites, EDAX (energy dispersive analysis X-rayspectroscopy) was also carried out in the fractured surfaces ofPV2. The Si relative wt % was found to be similar in variousplaces (two EDAX spectra are shown in the SupportingInformation, Figure S6). This indicates a relative uniformity inthe silica content in the matrix. In addition, to verify thepresence of silica in the composite matrix, TEM was carried outfor the composite (PV3) after dissolving the composite in

ethanol. TEM images showed the presence of aggregated silicain the composite matrix (Supporting Information Figure S7).

Thermal and Optical Properties of the Composites:TGA, DSC and UV - Visible spectroscopy. Thermogravi-metric analysis (Figure 6) of the composites shows that these

Figure 5. Fractured surface morphology of the pure polymer and the composites obtained from the tensile testing.

Figure 6. Thermogravimetric analysis of the polymer and thecomposites.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944389

composite materials are stable up to ∼360 °C (10%degradation). This is an important property for anencapsulation/passivation layer as it has to protect the deviceor important components over a long period of time. Noimprovement in the degradation temperature was observed asthe loading was increased (see the inset of Figure 6, the hightemperature region). Rather a significant decrease in thedegradation temperature (356 °C) was observed for PV3 withrespect to other compositions. This effect could be due to“agglomeration/cluster” formation of the silica particles insidethe hybrid matrix and hence a loss of integrity, which is alsoreflected in the mechanical properties (Table 2), as discussedearlier. In addition, the basic amine groups at the surface of thesilica particles may also catalyze the degradation, by thenucleophilic attack at the butyral fragments of the polymer.Since, in PV3 the relative amine group density is high due tohigher functionalized silica loadings, so the reduction in thedegradation temperature is more pronounced.DSC was carried out, in order to verify the effect of silica

loadings on the thermal history of the composites. In the DSCanalysis of the polymer as well as the composites, only glasstransition temperature (Tg) at ∼73 °C was observed (Figure 7)

in the specified temperature range (25−250 °C). It can be alsoobserved from DSC that Tg of the composites (PV1, PV2,PV3) did not change with respect to the neat polymer (PV0).Therefore, the increase in loading seems to have no effect onthe glass transition temperature. The DMA analysis (discussedlater) shows that Tg of the composites improves with theincrease in loadings of functionalized silica. The DSC trace ofthe as received powdered PVB is shown in Figure S8(Supporting Information). In the UV−visible spectra of thecomposites, a reduction of transmittance was observed with anincrease in loading (Supporting Information Figure S9). Thiscould be due to the increased silica particle density inside thematrix.DMA Analysis. The DMA results indicate an improvement

in the E′ (storage modulus) which is related to the elasticproperties of the material) from PV1 to PV2 (see theSupporting Information Figure S10), i.e. in the increase inthe functionalized silica content. Due to the better integrity andhomogeneity of the distribution of compatible functionalizedsilica in the polymer matrix, the storage modulus showed animprovement from PV1 to PV2. PV3 did not show anyimprovement in storage modulus as compared to PV1 and PV2,

which could be due to the aggregation effect, as observed fromthe tensile studies. It can be also observed that the relativechanges in the modulus values are small, which is due to thesmall relative increase of silica content in the composites.From DMA experiment, tan δ, which is a ratio of loss

modulus to storage modulus [E″/E′], can be obtained. This isrelated to the damping coefficient of the material. At the glasstransition (Tg) of a material, the tan δ (damping coefficient)value shows a maxima and hence a peak is observed in thecurve of tan δ as a function of temperature. Hence the glasstransition (Tg) temperatures of the composites can be observedfrom Figure 8 (tan δ vs temperature). It shows that the tan δ

value has shifted to a higher temperature with an increase in thesilica loading (PV1 71.7 °C, PV2 72.6 °C, and PV3 74.6 °C).This could be due to the better integration betweenfunctionalized silica nanoparticle and the polymer matrix athigher temperature under mechanical force. The betterintegration may be due to the hydrogen bonding interactionbetween silica surface −NH2 groups and the polar componentsof the polymer matrix. This improvement in the Tg was notresolved from the DSC analysis of the composites.

Contact Angle Measurement. Contact angle measure-ment values for the polymer and the nanocomposites areshown in the Table 2. On comparing with the neat polymer(87°), composites showed a reduced contact angle value(Figure 9). The reduction in the contact angle is due to theaddition of hydrophilic amine decorated silica particles in thematrix, which enhances the wettability of the matrix. Thisenhanced wettability can be further exploited in development ofsandwich/multilayered architecture with other polymer matrix.

Surface Morphology of the Composites. Opticalmicroscopy and scanning electron microscopy (SEM) wereused to observe the surface topography of the films, which areshown in Figure S11 (see the Supporting Information). Imagesshow the surface morphology and texture of the freestandingfilms. The images obtained from optical microscopy can becorrelated with the images of SEM, which shows the filmsurface is not uniform. The increase in the surface roughnesscould be also responsible for the enhancement of thewettability as observed from the contact angle.29

Swelling Study in Water. The composites show noswelling or weight increase, after they were immersed in the

Figure 7. DSC thermogram of the polymer and the composites.

Figure 8. Variation of tan δ with temperature.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944390

water for a period of ∼36 h. Similar behavior was previouslyobserved for PVB/TiO2 composites.30 The samples were alsokept in a humidity chamber (90% RH at 25 °C) for 72 h, andno increase in weight was observed. This swelling behavior is acritical property for the hybrid composites indicating that thehybrid is resistant to moisture and thus can be used forencapsulation.Permeability Measurement of the Composites: Cal-

cium Degradation Test. Permeability studies of thecomposites were carried out in order to observe the effect ofsilica loadings in the matrix. The variation of the inverse ofnormalized resistance (Ro/R) with time for the composites aswell as for the glue, at ≥95% RH and T = 35 ± 0.2 °C is shownin Figure 10. This degradation curve shows the moisture

permeation behavior/rate through the composite matrix. Withthe increase in the functionalized silica content, a reduction inthe moisture permeability was observed. The moisturepermeability for the neat polymer was found to be higherthan the composites. A huge reduction in permeability wasobserved in the composites from PV1 to PV2 and PV3. Since

the slope of (Ro/R) vs time varies at each point, the derivative(d(1/R)/dt) at every point was used and the permeabilityvalues at each time were calculated (Figure 11) depicting the

moisture permeability behavior through the polymer. Theaverage values of permeation rates at various time intervals aregiven in Table 3. The reduction in permeability is due to the

increase in number density of the mesoporous silica particles inthe polymer matrix, which provides a resistance for the watervapor. For PV1, the permeability is higher (less extendedtorturous pathway) since the number density of silica is less. Asthe number density increases for PV2 and PV3, permeabilitydecreases due to more extended torturous pathway, whichretards the movement of moisture molecules.In addition, as the number density of functionalized silica

increases, the number of amine groups also increases in thematrix. The amine group density of as prepared PV0, PV1, PV2,and PV3 can be calculated as 0, 37.37, 74.75, and 224.25 μmol,respectively. These values have been calculated from dataobtained from TGA, which showed a surface APTMS graftingdensity as 4.39 ± 0.3 μmol m−2 and BET, which showed asurface area of 679.6 m2 g−1. In Figure 12, the variation ofWVTR of the neat polymer matrix and the composites on theamine group density has been shown. This increase in the polaramine groups in the matrix also contributes to the relativereduction in the permeability of the composites. The polar−NH2 groups at the surface can also interact with moisturemolecules through hydrogen bonding and can retard thediffusion through the matrix.In the case of comparison between PV0 and the composites,

in addition to surface amine groups, the polyol also contributesto the reduction of permeability. The relative variation in

Figure 9. Contact angle values of the polymer and the compositesfilms.

Figure 10. Ro/R plot for the two composites and the glue.

Figure 11. Permeability value obtained from the slope of each point.

Table 3. Average WVTR (g m−2 day−1) for the Compositesat Various Time Intervals

average WVTR (g m−2 day−1)

composites 0−75 s 75−200 s 200−800 s 800 s−end

PV 0 0.24 3.24PV 1 1.58 3.05 5.6PV 2 0.26 0.08 0.07 0.12PV 3 0.10 0.10 0.11 0.67

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944391

permeability is not significant between PV2 and PV3 (Table 3),which could be due to aggregation of functionalized silica, eventhough the amine group density increased in the matrix.After the permeability test, the sealed film was peeled out

from the glass slide and SEM images were obtained for thedegraded calcium (calcium oxides/hydroxides species formedafter reaction with moisture, see Supporting Information FigureS12). This suggests that the permeation could be throughpinhole mediated moisture flow channels. The low permeabilityat such a high percent RH and temperature (acceleratedconditions) suggests that these composites can be used as abarrier material at ambient conditions at which the devices areoperated for practical applications.Diode Characteristics of the Devices under Accel-

erated Weathering. In order to illustrate the composite as amoisture barrier material, organic device encapsulation wascarried out. The encapsulated (with PV0 and PV3) andnonencapsulated organic Schottky structured diode devices(see Supporting Information Figure S2) were exposed to a RHof 90% at a temperature of 25 °C and current−voltage (I−V)characteristics were measured using a source-meter. After atime period of 0.5 h, the reduction in current densities withrespect to the initial current densities was calculated in a voltagerange of 0−1 V. The percentage change [100(Ii −If)/Ii; where Iiis the initial current density and If is the final current density] inthe current density for each device was calculated with respectto the initial current density over the 0−1 V range (Figure 13).This gives the reduction in current density with time underaging condition (90% RH and 25 °C) for all the devices. It canbe observed from Figure 13 that after 0.5 h, the relativereduction in current density is less (20 ± 5%) for the deviceencapsulated with PV3 than the diode, encapsulated with PV0(55% reduction) within the voltage range from 0 to 1 V. Whilein the nonencapsulated device, current density drops downrapidly to almost 97 ± 1%. This is due to the moisture barriercomposites, which protects the device from moisturepermeation, leading to device failure. The behavior of PV3and PV0 is inconsistent with the result observed from calciumdegradation test, i.e. the silica loaded composite reduces thepermeation of moisture and, therefore, shows lower reductionin current density of the diodes.

■ CONCLUSIONSThe properties of PVB film and PVB/functionalized meso-porous silica hybrid composite films were investigated forpotential use as an encapsulant for Schottky structured organicdevices. Thermal analysis of the films shows no significantchanges after functionalization but APTMS functionalized silicashowed improved mechanical properties. The fracture surfacemorphology shows more crack and cleavages (observed aftertensile testing) with an increase in the functionalized silicaloadings as compared to the neat polymer matrix. It indicatesthat the filler is compatible with the polymer matrix (higherinterfacial interaction between amine functionalized silicaparticles and the polymer matrix). However, higher loadingleads to agglomeration and results in the brittleness of the films,as observed from tensile testing. The degradation in theproperties was observed due to aggregation behavior; hence, anoptimization in functionalized silica loading is important forapplication purpose. The study reveals that the optimumloading is PV2. After this composition, various propertiesstarted deteriorating, due to aggregation of functionalized silica.An increase in silica loadings showed a reduction in water vaporpermeability. As compared to neat polymer PV0 (WVTR of3.24 g m−2 day−1), more than one order reduction in WVTR at35 °C has been observed in case of PV2 (WVTR of 0.08 g m−2

day−1) and PV3 (WVTR of 0.10 g m−2 day−1), as observedfrom calcium degradation test. The encapsulated devices werefound to be stable than nonencapsulated devices underaccelerated weathering condition. The device encapsulatedwith the neat polymer showed two times decrease in currentdensity, as compared to the composite film encapsulatedSchottky structured devices. The composite films did not showany swelling in water. Coupled with this property, an improvedmoisture barrier property of the composites as compared to theneat polymer (PV0) indicates that the composite material couldserve as a good encapsulant. Furthermore, the hybrid layers canbe integrated/sandwiched between two other polymer layers(like Surlyn, PET etc.) for further reduction in permeability.

■ ASSOCIATED CONTENT*S Supporting InformationFigure S1: Calcium degradation test setup (A) and moisturesensing device for calcium degradation test (B). Figure S2:

Figure 12. WVTR of various composites with amine group density ofthe respective composites.

Figure 13. Diode characteristic of the devices with and withoutencapsulation after 0.5 h at 90% RH at 25 °C.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944392

Schematic for weathering study of devices. Figure S3: Ramanspectra of neat and functionalized silica. Figure S4:thermogravimetric analysis of neat and functionalized silica.Figure S5: possible inter particle hydrogen bonding inter-actions. Figure S6: EDAX spectras of PV2 in various regionsand compositional analysis. Figure S7: TEM image of PV3 afterdissolution in ethanol. Figure S8: DSC thermogram of asreceived powdered PVB. Figure S9: UV−visible spectra of thepolymer and the composites. Figure S10: Variation of storagemodulus (E′) with temperature. Figure S11: SEM images (top)of the films and optical microscopy images (bottom) of neatpolymer and the composites. Figure S12: SEM image of thedegraded calcium layer after the calcium degradation test: afingerprint for permeation pathway. This material is availablefree of charge via the Internet at http://pubs.acs.org/.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: praveen@materials.iisc.ernet.in. Fax: +91-80-2360-0472. Tel.: +91-80-2293-2627.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSS.G. acknowledges the Council of Scientific and IndustrialResearch (C.S.I.R), New Delhi, for financial support andfellowship. The authors gratefully acknowledge Dr. RoyMohapatra and Mr. Harsabardhan of the Aerospace Engineer-ing Department, Indian Institute of Science, Bangalore, forDMA studies, Tribology lab, Mechanical Engineering depart-ment, for technical support, and Dr. G. S. Avadhani for TEMstudies, Department of Materials Engineering, Indian Instituteof Science, Bangalore, and Indian Institute of Science,Bangalore. In addition, the authors gratefully acknowledge thefinancial support from DST No SR/S3/ME/022/2010-(G) andtechnical support from IISc advanced facility for microscopyand microanalysis (AFMM), and NMR research centre.

■ REFERENCES(1) Chen, C. H.; Cheng, W. T.; Tsai, M. L.; Huang, K. T. Fabricationand Performance of Copper Phthalocyanine/Squaraine Dye/PeryleneComposite with Bulk Heterojunctions by the Solution BlendingProcess. Ind. Eng. Chem. Res. 2012, 51, 3630−3638.(2) Lu, X. W.; Wu, W.; Chen, J. F.; Zhang, P. Y.; Zhao, Y. B.Preparation of Polyaniline Nanofibers by High Gravity ChemicalOxidative Polymerization. Ind. Eng. Chem. Res. 2011, 50, 5589−5595.(3) Watanabe, S.; Fukuchi, Y.; Fukasawa, M.; Sassa, T.; Uchiyama,M.; Yamashita, T.; Matsumoto, M.; Aoyama, T. Electron Donor andAcceptor Spatial Distribution in Structured Bulk HeterojunctionPhotovoltaic Devices Induced by Periodic Photopolymerization.Langmuir 2012, 28, 10305−10309.(4) Smith, P. F.; Gerroir, P.; Xie, S.; Hor, A. M.; Popovic, Z.; Hair, M.L. Degradation of Organic Electroluminescent Devices. Evidence forthe Occurrence of Spherulitic Crystallization in the Hole TransportLayer. Langmuir 1998, 14, 5946−5950.(5) Qiu, Y.; Hu, Y. C.; Dong, G. F.; Wang, L. D.; Xie, J. F.; Ma, Y. L.H2O Effect on the Stability of Organic Thin-Film Field-EffectTransistors. Appl. Phys. Lett. 2003, 83, 1644−1646.(6) Pietro, R. D.; Fazzi, D.; Kehoe, T.; Sirringhaus, H. SpectroscopicInvestigation of Oxygen and Water Induced Electron Trapping andCharge Transport Instabilities in n-Type Polymer Semiconductors. J.Am. Chem. Soc. 2012, DOI: 10.1021/ja304198e.(7) Scurlock, R. D.; Wang, B.; Ogilby, P. R; Sheats, J. R.; Clough, R.L. Singlet Oxygen as a Reactive Intermediate in the Photodegradation

of an Electroluminescent Polymer. J. Am. Chem. Soc. 1995, 117,10194−10202.(8) Sutherland, D. G. J.; Carlisle, J. A.; Elliker, P.; Fox, G.; Hagler, T.W.; Jimenez, I.; Lee, H. W.; Pakbaz, K.; Terminello, L. J.; Williams, S.C.; Himpsel, F. J.; Shuh, D. K.; Tong, W. M.; Lia, J. J.; Callcott, T. A.;Ederer, D. L. Photo-Oxidation of Electroluminescent PolymersStudied by Core-Level Photoabsorption Spectroscopy. Appl. Phys.Lett. 1996, 68, 2046−2048.(9) Burrows, P. E.; Graff, G. L.; Gross, M. E.; Martin, P. M.; Hall, M.;Mast, E.; Bonham, C. C.; Bennett, W. D.; Michalski, L. A.; Weaver, M.S.; Brown, J. J.; Fogarty, D.; Sapochak, L. S. Gas Permeation andLifetime Tests on Polymer-Based Barrier Coatings. Proc. SPIE 2001,4105, 75−83.(10) Lewis, J. S.; Weaver, M. S. Thin-film permeation-barriertechnology for flexible organic light-emitting devices. IEEE J. Sel. Top.Quantum Electron. 2004, 10, 45−57.(11) Gupta, S.; Ramamurthy, P. C.; Madras, G. Synthesis andCharacterization of Flexible Epoxy Nanocomposites Reinforced withAmine Functionalized Alumina Nanoparticles: A Potential Encapsu-lant for Organic Devices. Polym. Chem. 2011, 2, 221−228.(12) Gupta, S.; Ramamurthy, P. C.; Madras, G. Covalent Grafting ofPolydimethylsiloxane over Surface-Modified Alumina Nanoparticles.Ind. Eng. Chem. Res. 2011, 50, 6585−6593.(13) Gupta, S.; Ramamurthy, P. C.; Madras, G. Synthesis andCharacterization of Silicone Polymer/Functionalized MesostructuredSilica Composites. Polym. Chem. 2011, 2, 2643−2650.(14) Gupta, S.; Ramamurthy, P. C.; Madras, G. MechanisticOverview of the Curing Behavior of Hydride Terminated Poly-dimethylsiloxane with Allyl Functionalized Alumina by Calorimetryand Rheometry. Thermochim. Acta 2011, 524, 74−79.(15) Lin, J. S.; Chung, M. H.; Chen, C. M.; Juang, F. S.; Liu, L. C.Microwave-Assisted Synthesis of Organic/Inorganic Hybrid Nano-composites and their Encapsulating Applications for PhotoelectricDevices. J. Phys. Org. Chem. 2011, 24, 193−202.(16) Dhaliwal, A. K.; Hay, J. N. The Characterization of PolyvinylButyral by Thermal Analysis. Thermochim. Acta 2002, 391, 245−255.(17) Nakane, K.; Kurita, T.; Ogihara, T.; Ogata, N. Properties ofPoly(vinyl butyral)/TiO2 Nanocomposites Formed by Sol−GelProcess. Compos. Part B: Eng. 2004, 35, 219−222.(18) Zhang, F. A.; Lee, D. K.; Pinnavaia, T. J. PMMA/MesoporousSilica Nanocomposites: Effect of Framework Structure and Pore Sizeon Thermomechanical Properties. Polym. Chem. 2010, 1, 107−113.(19) Jin, J.; Lee, J. J.; Bae, B. S.; Park, S. J.; Yoo, S.; Jung, K. H. SilicaNanoparticle-Embedded Sol−Gel Organic/Inorganic Hybrid Nano-composite for Transparent OLED Encapsulation. Org. Electron. 2012,13, 53−57.(20) Jung, K.; Bae, J. Y.; Park, S. J.; Yoo, S.; Bae, B. S. HighPerformance Organic Inorganic Hybrid Barrier Coating forEncapsulation of OLEDs. J. Mater. Chem. 2011, 21, 1977−1983.(21) Paetzolda, R.; Winnacker, A.; Henseler, D.; Cesari, V.; Heuser,K. Permeation Rate Measurements by Electrical Analysis of CalciumCorrosion. Rev. Sci. Instrum. 2003, 74, 5147−5150.(22) McCullough, R. D. The Chemistry of Conducting Poly-thiophenes. Adv. Mater. 1998, 10, 93−116.(23) Kumar, P.; Ranjith, K.; Gupta, S.; Ramamurthy, P. C.Electrochemical Copolymerization of Thiophene Derivatives; APrecursor to Photovoltaic Devices. Electrochim. Acta 2011, 56,8184−8191.(24) Bauer, F.; Ernst, H.; Decker, U.; Findeisen, M.; Glasel, H. J.;Langguth, H.; Hartmann, E.; Mehnert, R.; Peuker, C. Preparation ofScratch and Abrasion Resistant Polymeric Nanocomposites byMonomer Grafting onto Nanoparticles, 1 FTIR and Multi-NuclearNMR Spectroscopy to the Characterization of Methacryl Grafting.Macromol. Chem. Phys. 2000, 201, 2654−2659.(25) Rana, S.; Mallick, S.; Parida, K. M. Facile Method for Synthesisof Polyamine-Functionalized Mesoporous Zirconia and Its CatalyticEvaluation toward Henry Reaction. Ind. Eng. Chem. Res. 2011, 50,2055−2064.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944393

(26) Brunaur, S.; Emmett, P. H.; Teller, E. J. Adsorption of Gases inMultimolecular Layers. J. Am. Chem. Soc. 1938, 60, 309−319.(27) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.;Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. ReportingPhysisorption Data For Gas/Solid Systems - With Special ReferenceTo The Determination of Surface Area and Porosity. Pure Appl. Chem.1985, 57, 603−619.(28) Bordelanne, O.; Delville, M. Metal Oxide Modification viaTransition Metal Complexes: Hybrid Materials Characterizations andPotential Applications in Molecular Recognition. Sol. Stat. Sci. 2002, 4,851−858.(29) Gaume, J.; Taviot-Gueho, C.; Cros, S.; Rivatona, A.; Therias, S.;Gardette, J. L. Optimization of PVA Clay Nanocomposite for Ultra-Barrier Multilayer Encapsulation of Organic Solar Cells. Sol. EnergyMater. Sol. Cells 2012, 99, 240−249.(30) Nakane, K.; Ohashi, J.; Suzuki, F. Preparation and Properties ofa Composite of Poly(vinyl butyral) and Titania. J. Appl. Polym. Sci.1999, 71, 185−188.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie3022412 | Ind. Eng. Chem. Res. 2013, 52, 4383−43944394