Molecular dynamics simulations of uniaxial deformation of bimodal polyethylene melts.

Tensile deformation behavior of bimodal polyethylene (PE) was investigated by employing coarse-grained (CG) molecular dynamics simulations based on a united atom model. The bimodal PE was modeled by blending two linear polyethylene chains with different molecular weights. The mechanical response and corresponding conformational behaviors of the polymer melt during stretching were recorded as a function of strain under both high and low strain rates. We find that the tensile toughness was enhanced in an additive fashion by increasing the fraction of polymers with high molecular weight in bimodal PE. During elongation, the polymer chain extends and orients itself along the loading direction. Surprisingly, varying the bimodal distribution and the strain rates, the disentanglement does not synergistically follow the tendency of chain expansion and ordering along the tensile direction as the strain is gradually raised, implying that multiple deformation modes might exist during the plastic flow process. The molecular origin of this unique development of the entanglement network in bimodal PE is discussed in detail. Image 1 • Tensile mechanical response of bimodal PE melts is elastomer-like. • Bimodal distribution and strain rate both influence degree of orientational order. • Disentanglement is strongly coupled with intermolecular non-bond energy. [ABSTRACT FROM AUTHOR]