Polymer Nucleation under High-Driving Force, Long-Chain Conditions: Heat Release and the Separation of Timescales

This study reveals two important features of polymer crystal formation at high-driving forces in entangled polymer melts based on molecular dynamics simulations of polyethylene, a prototypical polymer. First, in contrast to existing literature on small-molecule crystallization, it is demonstrated that the heat released during polymer crystallization does not appreciably influence molecular-level structural details of early-stage, crystalline clusters (i.e., polymer crystal nuclei). Second, it is revealed that early-stage polymer crystallization (i.e., crystal nucleation) can occur without substantial chain-level relaxation and conformational changes, which is consistent with previous experimental work and yet in contrast to many previous computational studies. Given the conditions used to process polyethylene, the separation of timescales associated with crystallization and chain-level processes is anticipated to be of substantial importance to processing strategies. This study thus provides insights that highlight new research directions for understanding polymer crystallization under industrially-relevant conditions while also providing guidance as to how this work can be undertaken.