Study of the Mechanisms of Filler Reinforcement in Elastomer Nanocomposites

We performed a large-scale dissipative dynamics simulation to study the structural changes in unfilled and filled elastomers during uniaxial deformation, which helped to shed some light on the underlying reasons of filler reinforcement in rubber nanocomposites. Equilibrium stress-stain curves for different cross-linker concentrations and filler content were obtained, and their features were compared to the experimental data. Dependences of segmental orientation on deformation and true stress were studied; these dependences are discussed in the light of theoretical predictions and available experimental data. The structural changes in the deformed state were studied as well, namely, the dependences of mean end-to-end distance on the subchain length. For the filled elastomers it was found that in the matrix there are several sets of subchains with distinct properties. Part of the subchains which are not connected to the filler particles are deformed slightly more than in the unfilled matrix; the subchains connected to the filler particles are deformed significantly more. This "separation" is the main reason for reinforcement; its influence on the properties of the filled systems is discussed. In addition, the effect of the network topology (randomly cross-linked, end-linked, ideal diamond-like) on the mechanical properties of unfilled elastomers was studied.