Reinforcement of poly(dimethylsiloxane) networks by mica flakes

A poly(dimethylsiloxane) (PDMS) network was reinforced with spherical and plate-like particles. The shape, size distribution, aspect ratio, and surface area of the particles were examined by laser diffraction, gas adsorption, cation exchange, and scanning electron microscopy (SEM). The optimal ratio of cross-linker to PDMS precursor was ascertained from the mechanical properties of networks prepared with different cross-linker concentration. Homogeneous distribution of the filler in the polymer matrix as well as complete dispersion (disaggregation) of the particles are prerequisites for studying the influence of other parameters on the mechanical properties of composites. Mica platelets increased the elastic modulus of PDMS dramatically and were much superior to glass spheres with similar diameter. The modulus rose with increasing diameter and aspect ratio as well as with the volume fraction of the particles. The ultimate strength of the composite was also better enhanced by the plate-like particles than by spheres. However, the strength enhancement was less dramatic and the dependence on the particle size was reversed compared to that of the modulus. The tensile strength increased with increasing volume fraction of the filler but the rise was probably limited in the case of large particles by the emerging agglomeration at high loading. The ultimate elongation of the mica composites was comparable to that of glass spheres. The polymer chains did net intercalate the aluminosilicate layers of mica, as expected. (C) 2001 Elsevier Science Ltd. All rights reserved.