Entropy-Driven Preordering Assists Nucleation in Polyethylene

TL;DR

This study reveals that in polyethylene, preordering during nucleation is driven by entropy, specifically interchain translational entropy gain, challenging traditional enthalpy-driven models and providing new insights into polymer crystallization.

Contribution

The paper demonstrates that entropy, not enthalpy, drives preordering in polyethylene nucleation, offering a novel perspective on polymer nucleation mechanisms.

Findings

Preordering occurs before crystal nucleation in polyethylene.

Entropy gain from interchain translation drives preordering.

Flexible polymers with high entropy penalties can still nucleate rapidly.

Abstract

Non-classical two-step nucleation including preordering and crystal nucleation has been widely proposed to challenge the one-step nucleation framework in diverse materials, while what drives preordering has not been explicitly resolved yet. With molecular dynamics simulation, we find that two-step nucleation occurs in polyethylene, during which preordering precedes through the coupling between intrachain conformation and interchain orientation orders. Unexpectedly, preordering is driven by entropy rather than enthalpy, during which the interchain translational entropy gain compensates for the intrachain conformation entropy loss. This entropy-driven mechanism resolves the longstanding puzzle why flexible polymers with high entropy penalty still show high nucleation rate and opens a new perspective for understanding nucleation of synthetic and bio-polymers with conformation and orientation orders.