Mechanical Behavior of Polymer Nanocomposites: a discrete simulation approach
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Mechanical Behavior of Polymer Nanocomposites : a discrete simulation approach E. Chabert1, C. Gauthier1, R. Dendievel2, L. Chazeau1 and J.-Y. Cavaillé1 1 GEMPPM-INSA Lyon, 7 Avenue Capelle, 69621 Villeurbanne Cedex 2 GPM2-INPG, 101 Rue de la Piscine, 38402 Saint Martin d'Hères Cedex
ABSTRACT This work reports the dynamic mechanical characterization of nanocomposites based on a poly(butyl acrylate) matrix filled with spherical particles of either polystyrene or silica both of diameter around 100 nm. A discrete numerical simulation, taking into account the microstructure and the nature of contact between reinforcing particles has been developed. This simulation enables to quantify the effect of interactions between filler particles on the elastic modulus, and in a more general sense, to clarify the concept of mechanical percolation. It gives results in very good agreement with experimental data.
INTRODUCTION Nanocomposite materials consist of a nanometer-scale phase in combination with another phase acting as a matrix. Work about polymer nanocomposites has exploded over the last few years. Their properties are reported to be different from that of their micro-scale counterparts [1,2]. The specific features in nanocomposites are (i) the large interfacial area which can reach 100-1000 m2/g, (ii) the average distance between particles, down to a value comparable with the macromolecule coils. This can favor the short-distance filler-filler interactions leading, above a threshold fraction, to the formation of a network (percolation). Moreover, the presence of an interphase polymer layer near the inorganic surface with properties differing dramatically from the bulk polymer is often assumed. Due to the large surface area of the nanofillers, the interphase polymer is expected to dominate the properties of the nanocomposites. Though significant progress has been made in developing nanocomposites with different polymer matrices, a general understanding has yet to emerge. A major challenge to further development of nanocomposites is the lack of structure - properties modeling taking into account the influence of filler-filler and filler-matrix interactions.
MATERIALS AND EXPERIMENTAL RESULTS Nanocomposites materials were prepared using the emulsion polymerization route. PS and PBuA latexes were blended varying the PS content (from 10 to 45 vol. %). After film formation (35°C, 90 % of relative humidity), this process leads to rigid spherical PS fillers (d=110nm) randomly dispersed in a soft PBuA polymer matrix (these films are referred as "as dried" films). When PS-PBuA films have undergone an annealing treatment at 140°C (i.e. above the glass transition of the PS) for several hours, films were designated "annealed". Silica particles (Stöber synthesis [3]) with similar diameter (125 nm) were also introduced in the same PBuA matrix.
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