Effects of Entanglement on Polymer Crystal Growth and Intercrystalline Phase Formation
Lingyi Zou, Wenlin Zhang
Abstract
We apply atomistic molecular dynamics simulations to investigate the structural evolution in the intercrystalline phase of polyethylene (PE) during crystallization. Two crystalline seeds with various relative orientations and distances are placed in molten PE samples to trigger instantaneous crystallization under quiescent conditions. Using the Z1+ algorithm, we monitor the distributions and relaxation of entangled chains near the seeds during crystallization. We show that crystal growth requires alignment and disentanglement of polymer strands. As crystallization proceeds, the polymer dynamics become hindered near the crystals. A layer of trapped entanglement consisting of loops and ties accumulates near the crystal surface and, in turn, impedes the crystal growth. Our work also reveals the formation of the stress transmitters, including tie chains and entangled loops, in the amorphous regions. The tie-chain fraction increases with increasing molecular weight and decreasing intercrystal distance, which is well-described by a modified Huang–Brown model.