A Theoretical and Experimental Study of Filler Effect on Stress-Deformation-Segmental Orientation Relations for Poly(dimethylsiloxane) Networks

Results of stress−strain, infrared dichroism, and birefringence experiments on silica-filled poly(dimethylsiloxane) networks show strong upturns of the stress with increasing deformation while segmental-orientation-strain relations remain linear over the same deformation range. As a result of this difference, the stress−optical coefficient exhibits an unusual dependence on deformation. The upturn in the stress results from the limited extensibility of the chains, inferred from the upturns in the Mooney−Rivlin plots presented. To explain these observations from a molecular perspective, we characterized the end-to-end distributions of different length poly(dimethylsiloxane) chains by Monte Carlo isomeric state calculations and derived stress-deformation-orientation relations for networks made of these chains by employing the three-chain network model. The results of the molecular model, in parallel with experimental observation, show strong differences between stress and orientation behavior.