In this study, we address the question of the equivalent role of the pressure and temperature on the mechanical properties of highly filled elastomers. It is well known that in polymer matrixes, the equivalence of temperature and pressure results from free volume variations. Our measurements performed on phenylated polydimethylsiloxane (PDMS) chains filled with silica particles show that a temperature-pressure superposition property is still observed in both linear and nonlinear regimes in these systems. However, the temperature-pressure equivalence involves coefficients that are two orders of magnitude larger than those in non-reinforced matrixes. We suggest that the mechanical response of the filled elastomers is controlled by the shape of the rigid network made by fillers that are connected by rigid polymer bridges. In this frame, we provide quantitative evidence that the macroscopic behavior of reinforced elastomers is controlled by the variation in the degree of the confinement of polymer chains between particle surfaces.

It has been known for several decades that rubbers exhibit a hydrostatic pressure-temperature superposition, interpreted by the free-volume theory. Moreover, our experimental results, on a filled rubber, demonstrate a hydrostatic pressure-temperature superposition which is two orders of magnitude larger than the one observed in pure rubbers. A new physico-mechanical model is proposed to account for the hydrostatic pressure effect responsible for a local glass transition temperature shift. It is suggested that it comes from the change of distances between aggregates. The predicted shift, given by the model, is found to be consistent with experimental data.