Role of Glassy Bridges on the Mechanics of Filled Rubbers under Pressure

Abstract

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.

Relation between mechanical response of reinforced elastomers and dynamics of confined polymer chains

“…This is exactly what we observed experimentally in industrial samples as shown in Fig- ure 11 [34]. Experimentally, π * is of the order of a few MPa, which is in good agreement with the aforementioned estimation.…”

“…In the case of reinforced elastomers, pressure causes an increase in the elastic modulus, which can similarly be expressed in terms of an increase in the glass transition temperature. However, the increase in amplitude of the T g is approximately 50 K/MPa, two orders of magnitude larger than the one measured for a pure elastomer [34]. Under pressure, the density increases.…”

“…C. R. Physique -2021, 22, n S5,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] …”

Evidence of the Transition from a Flexible to Rigid Percolating Network in Polymer Nanocomposites

“…Over the past few decades, many attempts have been made to better understand how nanoparticles are connected in a PFN. ,− ,− Although there is a growing consensus that the formed PFN consists of fillers as the nodes and interfacial polymer layers as the bridges, − ,,− several fundamental questions concerning the dynamic nature of the polymer bridges and its relation to the mechanical reinforcement are still in active debate. ,,,,− The idea of a flexible PFN, in which the polymer bridge exhibits a flexible viscoelastic/rubbery response, has been widely accepted in the PNC community when studying the mechanical reinforcement in numerous PNCs at temperatures relatively far above the glass transition temperature ( T g ). ,,,,, On the other hand, Long and co-workers proposed the idea of a rigid PFN, in which the polymer bridge exhibits a rigid glassy response, for interpreting a marked increase in the mechanical reinforcement in PNCs upon approaching the T g . ,,− Despite a significant difference in the dynamic nature of polymer bridges in these reinforcement models, a recent study by Chen and co-workers theoretically predicted a possible transition from flexible to rigid PFN in PNCs by simply decreasing the filler size and/or increasing the filler fraction . The emergence of such a transition can provide important insights into understanding the reinforcement performance of PNCs as a function of temperature, filler characteristics, and filler/polymer interaction strength .…”

“…The emergence of such a transition can provide important insights into understanding the reinforcement performance of PNCs as a function of temperature, filler characteristics, and filler/polymer interaction strength . However, direct experimental observation evidencing the transition from flexible to rigid polymer bridges remains significantly challenging. ,, …”