Molecular dynamics simulations of nucleation details in stretched polyethylene

Molecular dynamics simulations were performed to investigate the microscopic mechanism of crystal nucleation in stretched polyethylene with different strains. The system consisted of 100 molecular chains, each containing 200 methylene groups. Polymer melts were first stretched to the states with different strains at a high temperature, and then the stretched polymers with different strains were further quenched to a low temperature for isothermal crystallization, respectively. Stretching causes local conformation transition from gauche-conformation to trans-conformation, together with segmental orientation along the stretching direction. Then, highly oriented segments with trans-conformation are further aggregated in local domains, which can be considered as the precursors for subsequent nucleation. During crystallization, most of crystallites originate from the precursors. Furthermore, the detailed process of crystal nucleation is closely related to strain. At low strains, the uncorrelated oriented nuclei containing trans-conformation connected by chain-folding appear. At high strains, the oriented nuclei containing trans-conformation with intermolecular alignments connected by ties dominate.