Chain dimensions in polysilicate-filled poly(dimethyl siloxane)

We present experimental results on the single chain dimensions of isotopic blends (both mismatched and matched molecular masses) of poly(dimethyl siloxane) (PDMS) containing trimethylsilyl-treated polysilicate particles (fillers) and compare these results with Monte Carlo calculations. For polymer chains which are approximately the same size as the filler particle, a decrease in chain dimensions is observed relative to the unfilled chain dimensions at all filler concentrations. For larger chains, at low filler concentrations, an increase in chain dimensions relative to the unfilled chain dimensions is observed. Both results are in agreement with existing Monte Carlo predictions. However, at even higher filler contents, which are beyond the scope of the Monte Carlo predictions, the chain dimensions reach a maximum value before decreasing to values which are still larger than the unfilled chain dimensions. A simple excluded volume model is proposed which accounts for these observations at higher filler content.