Deformation Behavior of Homogeneous and Heterogeneous Bimodal Networks

Abstract

In this study, the effect of spatial heterogeneities on the deformation behavior during uniaxial elongation as well as the ultimate properties of bimodal gels consisting of both short and long chains was investigated by molecular simulations. Defect-free networks were created containing dense short-chain clusters and compared with gels having a homogeneous distribution of chains. In both cases, the first chains to rupture were the ones already aligned along the strain axis prior to imposing a strain. The presence of clusters was generally not found to improve the ultimate stress or toughness; the short chains within the clusters were effectively shielded from deformation, even at large fractions of short chains. The heterogeneous network tended to be weaker than the corresponding homogeneous network at a given fraction of short chains, fracturing before any significant deformation of clusters had taken place. The deformation behavior was, however, found to be sensitive to the degree of heterogeneity and the number of intercluster connections. At large fractions of short chains, clustering offered an improvement in the ultimate strain compared to a homogeneous bimodal network and also an equivalent unimodal network with the corresponding number-average chain length, thus providing a small improvement in toughness.

Strain Softening of Bimodal Isoprene Rubber Vulcanizates

“…In the IR/LIR vulcanizates at similar ν e , the deformational stress at given strains increases significantly with increasing LIR content ( Figure ), which could be ascribed to the short strands being forced to align and break prior to the long strands. [ 64,80 ] The IR‐10LIR vulcanizate shows the highest tensile strength corresponding to highest values of the energy required for rupture. [ 60 ] The multimodally distributed network strands make unusually tough elastomers in which the short strands elevate deformational stress and the relatively long strands retard the ultimate rupture.…”