EpoxyâAmine Based Nanocomposites Reinforced by Silica

ARTICLE pubs.acs.org/JPCC

Epoxy Amine Based Nanocomposites Reinforced by Silica Nanoparticles. Relationships between Morphologic Aspects, Cure Kinetics, and Thermal Properties Camille Alzina, Nicolas Sbirrazzuoli, and Alice Mija* Thermokinetic Group, Laboratory of Chemistry of Organic and Metallic Materials CMOM, University of Nice Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 2, France

bS Supporting Information ABSTRACT: In general, the incorporation of nanoparticles into polymers shows an increase of the materials performances, but the effect of the nanosized objects is still not well understood. In this study, we have investigated the impact of incorporation of silica nanoparticles in an epoxy/ amine (DGEBA/mPDA) system. Naked silica nanoparticles (SiNP) were synthesized via a sol gel technique. To evaluate the interfacial effect on properties of nanocomposites, the surface of the nanoparticles was modified by substituting silanol groups into epoxide functions (SiNPEp). A new method was elaborated for obtaining different organic inorganic nanocomposites with a very good dispersion without any aggregation according to transmission electron microscopy (TEM) analyses. The influence of the different silica nanoparticles (SiNP or SiNPEp) on the mechanisms of the reaction between epoxy and amine groups is highlighted. Important new inputs on the cure kinetics of the epoxy/amine mixture are given. The glass transition temperatures and thermal properties of nanocomposites have been examined, and relationships have been established.

1. INTRODUCTION Over the past decades, the combination of inorganic or organic inorganic hybrid nanoparticles with polymers enlarged the field of properties of these materials. These nanocomposites showed various applications in the domain of adhesives, coatings, and bulk composites or for optical applications as examples.1,2 The considerable increase of the interfacial area between the fillers and the polymeric matrix considerably improves the overall properties of polymers containing nanosized inorganic fillers. Among different materials, epoxy amine based polymers are intensively used in the industry for a wide variety of applications due to their physical properties such as thermal stability, mechanical strength, or chemical resistance.1 Silica nanoparticles (SiNP) are interesting inorganic materials for the reinforcement of epoxy/amine based systems. The physical properties of the nanocomposites are strongly related to the nature of nanoparticles such as their size and shape but also their dispersion in the polymer matrix. Zheng et al.3 studied the effects of the dispersion of silica nanoparticles on the mechanical properties of the nanocomposites and highlighted that functionalized SiNP allow a better dispersion in comparison with the naked SiNP. Investigations on the glass transition temperature (Tg) of the material showed that the size, loading, and dispersion conditions of the SiNP are important factors.4 The nature of the interactions at the interface of inorganic particles and the organic polymer matrix are crucial for having a good homogeneity at the nanoscale size. The surface modification of SiNP can be carried out using different methods. The use of r 2011 American Chemical Society

surfactants5 or the adsorption of macromonomers6 on the silica surface are techniques based on physical interactions and can be used for the functionalization. Different chemical reactions can be performed in order to conjugate different functional groups7 or to coat directly the polymer on the SiNP surface.8 Herein, we describe how the introduction of epoxy functionalized SiNP into the tridimensional network of an epoxy amine polymer affects the thermal properties of the polymer in comparison with those of naked SiNP. In order to obtain nicely dispersed epoxy functionalized SiNP in the epoxy matrix, we develop a new method of synthesis based on the work of Kang.9 Important modifications on the mechanisms of the reaction between epoxy and amine groups in the presence of SiNP and SiNPEp are highlighted, using differential scanning calorimetry (DSC) data and nonlinear isoconversional analysis.10,11 The catalytic effect of the nanoparticle surface is underscored, and the changes in the kinetic pathways at the molecular level are responsible for the modifications of the macroscopic properties of the final nanocomposites.

2. EXPERIMENTAL SECTION 2.1. Materials. Tetraethoxysilane (TEOS), potassium iodide (KI), 18-crown-6 ether, epichlorohydrin, bisphenol A diglycidyl Received: July 12, 2011 Revised: September 19, 2011 Published: October 03, 2011 22789

dx.doi.org/10.1021/jp2066259 | J. Phys. Chem. C 2011, 115, 22789–22795

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Figure 1. Synthesis of epoxy functionalized silica nanoparticles SiNPEpA and SiNPEpB.

ether epoxy resin (DGEBA), m-phenylenediamine (mPDA), and the solvents were purchased from Sigma-Aldrich and used without further purification. 2.2. Preparation of Silica Nanoparticles. 2.2.1. Synthesis of Naked Silica Nanoparticles (SiNP). Silica nanoparticles (SiNP) were synthesized using a sol gel technique developed by St€ober et al.12 by hydrolysis of tetraethylorthosilicate Si(OC2H5)4 (TEOS) in ethanol catalyzed by ammonia. Following the reaction conditions, nanoparticles within different sizes (between 10 nm and 2 μm) can be obtained. Silica nanoparticles with a theoretical size of 113 nm were obtained following the procedure described in the literature.12 A 47.25 g sample of an aqueous solution containing 28% NH4OH was diluted in technical ethanol (96%) in order to obtain 1 L of solution. A 208.3 g sample of TEOS dissolved in technical ethanol (1 L final volume) was slowly added to the NH4OH solution, and the mixture was stirred at 500 rpm over 12 h at room temperature. The nanoparticles were kept in the reaction medium. The mass of nanoparticles per volume of solution was determined after evaporation to dryness of a defined volume of solution. 2.2.2. Surface Modification of Silica Nanoparticles by Epoxidation (SiNPEp). Previously synthesized silica nanoparticles were chemically modified by epoxidation with epichlorohydrin using two different methods. First, the procedure described by Kang et al.9 (method A) was applied (Figure 1). The SiNP are previously dried under vacuum, and the reaction with epichlorohydrin in the presence of KI and 18-crown-6 ether used as catalyst is carried out at 130 °C for 24 h under vigorous stirring. Catalysts and excess of reagents were removed by several dilutions in acetone and centrifugation. The functionalized SiNPEpA nanoparticles were kept in acetone for further experiments. In a second method, we used solvated instead of dried SiNP (method B). The solution of SiNP was several times diluted in toluene and centrifuged to eliminate ethanol and ammonia. The SiNP were kept in a minimum of toluene, and the reaction with epichlorohydrin and purification were carried out as described above to afford the SiNPEpB. 2.3. Preparation of Epoxy/Silica/Amine Nanocomposites. 2.3.1. Incorporation of Silica Nanoparticles SiNP into Epoxy DGEBA Resin. The solution of SiNP in ethanol and ammonia was diluted in toluene and evaporated under reduced pressure until total removal of ammonia. DGEBA dissolved in acetone was then added and the mixture DGEBA/SiNP (ratios w/w 80/20 and 90/10) was evaporated to dryness under high vacuum after stirring and homogenization. 2.3.2. Incorporation of Modified Silica Nanoparticles SiNPEp into Epoxy DGEBA Resin. Four blends based on DGEBA/SiNPEpA

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and DGEBA/SiNPEpB (ratios 80/20 and 90/10) were obtained following the same procedure by mixing the functionalized SiNPEpA or SiNPEpB with DGEBA in acetone followed by evaporation under vacuum. 2.3.3. Preparation of Epoxy/Silica/Amine Thermoset Nanocomposites. Thermosetting nanocomposites were obtained by adding the curing agent mPDA previously warmed to 70 °C to an epoxy/silica mixture in order to have stoichiometric epoxy/amine proportions, taking into account the epoxy functions present on SiNPEpA or SiNPEpB. Determination of the thermodynamic (T, t) curing program requires running a series of preliminary DSC experiments under dynamic or isotherm conditions. In order to obtain a maximum cured material, three continuous stages of temperature were conducted. We cured the system using an isotherm program: at 75 °C for 2 h, at 125 °C for 2 h, and a last isotherm at 185 °C during 2 h was added in order to measure Tg∞. 2.4. Techniques. Fourier transform infrared (FTIR) spectra were obtained using a Perkin-Elmer Paragon 1000 spectrophotometer at room temperature with a resolution of 4 cm 1 ranging from 4000 to 400 cm 1. The dried nanoparticles were analyzed after dispersion in KBr in reflective diffusion mode. A drop of TEOS was analyzed between two KBr windows in transmission mode. The granulometric size and distribution of silica nanoparticles were estimated by a Zetasizer Nano ZS from Malvern. The epoxy equivalent weight (EEW) was titrated using potentiometry.13 Differential scanning calorimetry (DSC) measurements were carried out on a DSC 823e from Mettler-Toledo. The apparatus is equipped with an HSS7 ceramic sensor (heat-flux sensor with 2 120 thermocouples, Au Au/Pd), which allows very high sensitivity. Temperature and enthalpy calibrations were performed by using indium and zinc standards. Integrations of DSC peaks were done using a straight baseline. Samples of about 10 mg were placed in 40 μL aluminum crucibles. An advanced isoconversional method10,14 16 was applied at four different heating rates (1, 2, 3, 4 °C 3 min 1) to compute the Eα dependence vs conversion α. The dispersion of the silica nanoparticles within the matrix was controlled by transmission electronic microscopy (TEM). The TEM images were obtained from a Philips CM12 using an accelerator voltage of 120 kV. Before analysis, the samples were cut with an ultramicrotome. The thermogravimetric measurements were made on a TGA 851e from Mettler-Toledo. The microbalance has a precision of (0.1 μg and is kept at constant temperature (30 °C) during analyses to avoid the variation of weight measurement with temperature. Samples of about 10 mg were placed into 70 μL alumina pans. The samples were heated from 30 to 900 °C at 5 °C 3 min 1 under a nitrogen flow of 50 mL 3 min 1.

3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization of Silica Nanoparticles and Epoxy-Based Nanocomposites. The synthesized silica

nanoparticles were analyzed by FTIR spectroscopy showing a total conversion of the organosilane TEOS into nanoparticles (see Figure S1 in the Suppporting Information). SiNP size dispersity was evaluated at 88 nm by dynamic light scattering (DLS) which is in the range of the theoretical size determined by St€ober equations (see Figure S2 in the Suppporting Information). TEM investigations demonstrated the presence of spheric SiNP with an average size in accordance with the value obtained by DLS (see Figure S3 in the Suppporting Information). 22790

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We first used the method of Kang et al.9 (method A) for the epoxy silica nanoparticle functionalization (SiNEpA). In this method, the SiNP starting materials are dried and then reacted with epichlorhydrin in the presence of KI and 18-crown-6 ether. The drying of the SiNP induces the formation of aggregates that are not dispersed during the modification, affording a partial functionalization and a latter poor dispersion of the SiNPEpA into the epoxy matrix (DGEBA). In order to circumvent these drawbacks, we chose to use solvated SiNP as starting materials (method B). Several cycles of dilution/centrifugation in toluene were applied for the removal of the ethanol and ammonia from the mother solution. Using the B method, the SiNP do not aggregate, being dispersed in the solvent and so can fully react with the epichlorhydrin. The resulting SiNPEpB showed a good dispersion in the DGEBA, without aggregation. The FTIR spectra of SiNPEpA and SiNPEpB highlight the functionalization of the SiNP with characteristic bands between 3000 and 2800 cm 1 of the methylene of the epoxy group (see Figure S1 in the Suppporting Information). The epoxy equivalent weights (EEWs) of the different mixtures were determined by potentiometry, and the values are resumed in Table 1. According to the EEW of DGEBA equal to 175.2, the theoretical value of the mass of the epoxy mixture DGEBA/SiNP 80/20 should be of 219, which is close to the experimental value (222.8). For mixtures containing SiNPEpA or SiNPEpB, the values of the EEWs are very different depending on the mode of incorporation of silica in the

resin. The EEW of SiNPEpA is close to the value of the mixture with SiNP and is higher than that of SiNPEpB. This suggests that the SiNP epoxy functionalization by method A is less effective or that the silica is in the form of aggregates; therefore, few epoxide functions are measured. The dispersion of the different nanoparticles in epoxy-based nanocomposites was evaluated by TEM analyses (Figures 2 and 3). The SiNPEpB were better dispersed in the DGEBA matrix. Functionalized nanoparticles obtained by the method described by Kang et al.9 (SiNPEpA) gave larger aggregates with SiNPEpB nanoparticles well dispersed in the matrix. Due to the poor dispersion of the SiNPEpA, DGEBA/SiNP and DGEBA/SiNPEpB systems were chosen for further studies. 3.2. Influence of Silica Nanoparticles on the Cure Kinetics and Reaction Mechanism. Hydroxymethyl groups are known to have a catalytic effect on the epoxy ring-opening reactions, acting as hydrogen-bond donor molecules.17 19 Thus, addition of silica nanoparticles could modify the kinetic pathways of the epoxy amine additions, facilitating the ring-opening reactions. This catalytic effect is illustrated by the DSC data (Figure 4). The

Table 1. Epoxy Equivalent Weights (EEWs) Determined by Potentiometry resin EEW (g 3 equiv1 ) DGEBA

175.2

DGEBA/SiNP

90/10

205.9

DGEBA/SiNP

80/20

222.8

DGEBA/SiNPEpA DGEBA/SiNPEpA

90/10 80/20

198.5 218.7

DGEBA/SiNPEpB

90/10

187.3

DGEBA/SiNPEpB

80/20

202.9

Figure 4. DSC data of the heat release during nonisothermal cures of different mixtures at 3 °C 3 min 1. Solid stars, DGEBA/mPDA system; open squares, DGEBA/SiNP/mPDA 80/20 system; open triangles, DGEBA/SiNPEpB/mPDA 80/20 system.

Figure 2. TEM micrographs of 80/20 epoxy/silica mixture: (a) DGEBA/SiNP/mPDA; (b) DGEBA/SiNPEpA/mPDA; (c) DGEBA/SiNPEpB/ mPDA (scale bar =2 μm).

Figure 3. TEM micrographs of 90/10 epoxy/silica mixture: (a) DGEBA/SiNP/mPDA; (b) DGEBA/SiNPEpA/mPDA; (c) DGEBA/SiNPEpB/ mPDA (scale bar =2 μm). 22791



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Figure 5. Proposed mechanisms for the reaction between epoxy and amine groups in the presence of SiNP and SiNPEp.

thermoanalytical curves show that incorporation of SiNP shifts the thermal event associated with epoxy amine addition to lower temperature. This can be attributed to the catalytic effect in the presence of Si OH of silica particles (DGEBA/SiNP/mPDA system).20,21 As shown in Figure 4, the shape of the DSC curve is also modified in the presence of nanoparticles. This may indicate a change in the kinetic parameters16 designating that different mechanisms occur in this case. Indeed, the protonation of epoxy in the presence of acidic hydroxyl groups Si OH, which act as an epoxy ring-opening initiator due to the release of a proton H+, produces a highly reactive oxonium ion (Figure 5). This reaction enters into competition with the ring opening produced by epoxy amine addition. As indicated by DSC data in Figure 4, addition of functionalized SiNPEpB does not affect the heat flow rate (DGEBA/SiNPEpB/mPDA system), indicating that functionalization of the Si OH groups is total, or that only part of the hydroxyl groups were functionalized but the inserted epoxy groups hinder the accessibility of the Si OH groups, preventing the hydroxyl groups from acting as a catalyst. Isoconversional methods can be helpful for the elucidation of reaction mechanisms of complex cures,16,22,23 because the Eα dependencies may reflect changes in the rate-limiting steps of the overall process of polymer cross-linking. An advanced isoconversional method14,15 was applied to these systems, and the results are presented in Figure 6a. The systems DGEBA/mPDA and DGEBA/SiNPEpB/mPDA show very similar Eα dependencies vs extent of conversion (Figure 6a). This indicates that the rate-limiting steps and the overall reaction mechanism of the two systems are very similar. This conclusion is in good agreement with the hypothesis of full functionalization of the SiNPEpB. On the contrary, the mixtures DGEBA/mPDA and DGEBA/SiNP/mPDA show very different Eα dependencies at the beginning and end of the reaction. Depending on the heating rate, the same value of α is accomplished at different temperatures, and this was used for evaluating an average temperature associated with the α value (Tα). The resulting Eα versus Tα dependence is shown in Figure 6b. This dependence allows us to correlate the Eα values

with temperature. Because the two chemical reactions do not occur in the same temperature interval, the conversion degrees are not related to the same reaction temperature. Thus, analysis of Figure 6b can give additional information on the cure kinetics of the system with and without silica nanoparticles. Addition of SiNP leads to a higher decrease of Eα at the beginning of the reaction (0.02 < α < 0.10, Figure 6a) characteristic of autocatalytic reactions.24 Thus, hydroxyl groups present on the SiNP promote catalytic reactions because the generated oxonium ion may reacts with an epoxy group, entering into competition with the mPDA curing agent. Then, the epoxy ring can react with the oxonium ion to form ether links. For the DGEBA/SiNP/mPDA system, the characteristic decrease of Eα reported for the catalytic effect is greater, in agreement with the hypothesis of an easier ring opening in the presence of SiNP. The addition of SiNP shifts the reaction to lower temperatures. Higher apparent activation energy values are obtained for the system DGEBA/SiNP/mPDA. However, these higher Eα values reported in Figure 6a for the system DGEBA/SiNP/mPDA as a function of the relative extent of conversion correspond to lower temperature, where the reaction of the system DGEBA/mPDA is negligible. Thus, we can conclude that these higher Eα values correspond mainly to the ring opening initiated by the hydroxyl groups of SiNP, rather than epoxy amine addition.16 On the other hand, the comparison of Eα dependencies as a function of temperature (Figure 6b) shows that the values are always slightly lower in the chemically controlled part of the reaction when silica nanoparticles are added. After the early autocatalytic stages of the reaction (α > 0.10), it was shown that the overall reaction is mainly controlled by primary amine addition.22 For 0.30 < α < 0.90, a competition takes place between secondary amine addition and diffusion control. During this conversion interval of the reaction, the rate of reactant diffusion becomes the rate-determining factor, with the molecular motion being hindered. Once the epoxy curing system has passed the gel point, the small molecules can restart chemical reactions. Gelation corresponds to the region where the overall reaction, being initially chemically controlled, starts to 22792



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Table 2. Tg Values of the Different Materials materials Tg (°C) DGEBA/mPDA

Figure 6. (a) Eα dependencies versus conversion rate α. Solid stars, DGEBA/mPDA system; open squares, DGEBA/SiNP/mPDA 80/20 system; open triangles, DGEBA/SiNPEpB/mPDA 80/20 system. (b) Eα dependencies versus temperature. Solid stars, DGEBA/mPDA system; open squares, DGEBA/SiNP/mPDA 80/20 system; open triangles, DGEBA/SiNPEpB/mPDA 80/20 system.

become diffusion controlled.22 The diffusion control is associated with activation energy values as low as Eα ∼ 10 20 kJ 3 mol 1 when the system enters the glassy state. The resulting value (∼20 kJ 3 mol 1) is too small to activate primary or secondary amine additions or etherification. However, this value is typical for the activation energy of diffusion of small molecules.25 For a higher extent of conversion α < 0.80 0.90, a competition takes place between the control by diffusion of the monomers and oligomers, and the beginning of etherification reactions. As seen in Figure 6, the characteristic Eα decrease associated with the diffusion phenomena occurring at the end of the reaction (0.65 < α < 0.85 0.90) is less pronounced in the DGEBA/SiNP/mPDA system. It was shown that etherification occurs at high temperature and is associated with high activation energy (Eα ∼ 100 kJ 3 mol 1).23 The resulting Eα increase for higher extent of conversion (0.90 < α < 0.98) has been associated with the temperature range where etherification and homopolymerization start to become significant, and can be explained by

176

DGEBA/SiNP/mPDA

90/10

DGEBA/SiNP/mPDA

80/20

168 166

DGEBA/SiNPEpA/mPDA

90/10

164

DGEBA/SiNPEpA/mPDA

80/20

164

DGEBA/SiNPEpB/mPDA

90/10

173

DGEBA/SiNPEpB/mPDA

80/20

172

the possibility of reactivation of chemical reactions due a higher molecular mobility of the medium.23 Thus, etherification reactions become significant at lower values of the relative extent of conversion, (i.e., lower T value) due to the catalytic effect of SiNP. As a result, the Eα dependency starts to increase for lower α value (Figure 6a), i.e., for lower T value (Figure 6b). This change in the rate-limiting step of the overall polymer crosslinking becomes significant at lower temperature when SiNP are added. In contrast, the Eα dependencies of DGEBA/mPDA and DGEBA/SiNPEpB/mPDA systems are very similar over the whole range of extent of conversion. The diffusion control is slightly less important for the epoxy functionalized silica nanoparticles system. Indeed the nanoparticles are included in the polymer network; mesh is therefore more important and molecular mobility is slightly higher. Chemical reactions continue and the decrease of Eα is lower for the DGEBA/SiNPEpB/mPDA systems. This is in agreement with a lower cross-linking density and lower Tg values as confirmed by results presented in section 3.3. 3.3. Glass Transition Temperature. Tg values of thermoset materials were obtained by DSC measurements (Table 2). The incorporation of 10 or 20% naked silica nanoparticles in DGEBA/mPDA decreases the Tg of the material about 8 10 °C (reference, 176 °C; 10% SiNP, 168 °C; and 20% SiNP, 166 °C). Introduction of SiNPEpA nanoparticles leads to a similar effect, leading to a decrease of the Tg of the material of 12 °C. However, the Tg of the materials DGEBA/SiNPEpB/mPDA for 10 and 20% contents (respectively 173 and 172 °C) showed a lower difference from the reference material regarding the materials containing SiNEpA. These values reflect the very good dispersion of SiNPEpB nanoparticles in the matrix. In contrast, the materials obtained by method A showed a lower Tg because of the aggregation of silica nanoparticles (Figures 2 and 3). 3.4. Thermal Stability. Thermogravimetric analyses of thermoset nanocomposites are presented in Figure 7. The degradation of DGEBA/mPDA reference material initiates at about 350 °C. When silica nanoparticles were added, the material started to degrade at a slightly lower temperature, especially when silica nanoparticles were poorly dispersed (method A). The material containing 10% SiNPEpB nanoparticles and the nanocomposites containing the naked silica nanoparticles were the ones whose degradation profiles were nearest the material DGEBA/mPDA. Three reasons are at the origin of this order of degradation. First, the organic materials grafted on the SiNPEpA and SiNPEpB are degraded at lower temperature; the linkage Si O C is poorly stable. In addition, a good dispersion of nanoparticles in the matrix leads to a more tortuous way of escape for the 22793



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loads while epoxy functionalized SiNPEpB reacted with amine and were included in the three-dimensional network of the material. Kinetic studies revealed a catalytic effect of SiNP due to the presence of hydroxyl groups on the surface of nanoparticles where the epoxy functionalized SiNPEpB did not affect the kinetics of polymerization of the epoxy amine thermosetting system. The present study gives new insight into the influence of the different silica nanoparticles on the mechanisms of the reaction between epoxy and amine groups. Etherification reactions become significant at lower temperatures when SiNP are added due to their catalytic effect. The incorporation of SiNP in the system DGEBA/mPDA decreased the Tg of the material. This decrease is less important when well-dispersed epoxy functionalized SiNPEpB were incorporated due to their integration into the three-dimensional network of the material. The general method developed here for silica nanoparticles using isoconversional analysis can be applied to other crosslinked systems for a better understanding of the mechanisms involved at the interface nanofiller/matrix during polymerization and linking them to the macroscopic properties of the resulting polymer.

’ ASSOCIATED CONTENT

bS

Supporting Information. FTIR spectra, DLS results, and TEM images of the silica nanoparticles. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

Figure 7. Thermogravimetric stability of different materials: stars, DGEBA/mPDA system; squares, DGEBA/SiNP/mPDA 90/10 system; circles, DGEBA/SiNPEpA/mPDA 90/10 system; triangles, DGEBA/ SiNPEpB/mPDA 90/10 system.

degraded compounds. These explain why the degradation occurs faster in the presence of SiNPEpA than with SiNEpB and finally with SiNP in accordance with the TEM analyses. A faster degradation of the polymer could be expected without nanoparticles since the way of escape is less tortuous. However, the presence of nanoparticles increases the distance of the crosslinking nodes that decreases the cross-linking density and leads to lower Tg and faster degradation in comparison with the reference polymer DGEBA/mPDA.

4. CONCLUSIONS The synthesis of silica nanoparticles by a sol gel process was carried out to obtain individual nanoparticles. These silica nanoparticles were functionalized by epoxidation and inserted into an epoxy DGEBA matrix. A new route of nanocomposite elaboration was achieved, giving a very good dispersion. This study determined the effects of the incorporation of silica nanoparticles on the properties of an epoxy amine thermosetting system. The naked silica nanoparticles, SiNP, behaved as

’ ACKNOWLEDGMENT The authors acknowledge the PACA region and SICOMIN Composites for financial support. Thanks to Dr. Franc-oise Giulieri for her advice on the silica nanoparticle synthesis. The authors also wish to thank Dr. Urs Joerimann, Dr. Franck Collas, and Laurent Zoppi from Mettler-Toledo Inc. for fruitful collaboration and scientific exchanges. ’ REFERENCES (1) Hussain, F.; Hojjati, M.; Okamoto, M.; Gorga, R. E. J. Compos. Mater. 2006, 40 (17), 1511–1575. (2) Zhang, S.; Sun, D.; Fu, Y.; Du, H. Surf. Coat. Technol. 2003, 167 (2 3), 113–119. (3) Zheng, Y.; Zheng, Y.; Ning, R. Mater. Lett. 2003, 57, 2940–2944. (4) Sun, Y.; Zhang, Z.; Moon, K.-Z.; Wong, C. P. J. Polym. Sci., Part B: Polym. Phys. 2004, 42, 3849–3858. (5) Wu, T.-M.; Chu, M.-S. J. Appl. Polym. Sci. 2005, 98, 2058–2063. (6) Reculusa, S.; Poncet-Legrand, C.; Perro, A.; Duguet, E.; BourgeatLami, E.; Mingotaud, C.; Ravaine, C. Chem. Mater. 2005, 17, 3338–3344. (7) Liu, Y.-L.; Hsu, C.-Y.; Wang, M.-L.; Chen, H.-S. Nanotechnology 2003, 14, 813–819. (8) Ruan, W. H.; Mai, Y. L.; Wang, X. H.; Rong, M. Z.; Zhang, M. Q. Compos. Sci. Technol. 2007, 67, 2747–2756. (9) Kang, S.; Hong, S. I.; Choe, C. R.; Park, M.; Rim, S.; Kim, J. Polymer 2001, 42, 879–887. (10) Vyazovkin, S.; Sbirrazzuoli, N. Macromol. Rapid Commun. 2006, 27, 1515–1532. 22794



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EpoxyâAmine Based Nanocomposites Reinforced by Silica

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EpoxyâAmine Based Nanocomposites Reinforced by Silica