Orientation Mismatch Induces Suppressed Nucleation in Equi-Biaxial Stretch-Induced Polymer Crystallization

Stretch-induced crystallization (SIC) under equi-biaxial deformation remains poorly understood due to the complex interplay between multiaxial strain fields and molecular orientation. Herein, we employ molecular dynamics simulations to investigate SIC in polymer melts subjected to equi-biaxial stretching, focusing on the role of segment orientation anisotropy in nucleation. By varying the Deborah number ( De )─a dimensionless parameter characterizing the ratio of chain relaxation time to deformation time─we reveal two distinct nucleation regimes: for De < 10, nucleation is accelerated by segment orientation, with shorter induction times correlating with higher orientational order parameter b s; conversely, for De > 10, nucleation is unexpectedly suppressed despite enhanced segment orientation, with induction times increasing monotonically with De . This counterintuitive suppression arises from an “orientation mismatch” mechanism: equi-biaxial stretching induces planar segment orientation (elevated b s and c s, where c s quantifies deviation from cylindrical symmetry), whereas nucleation requires cylindrical orientation (increasing b s but decreasing c s ). an Arrhenius-type model confirms that the transition from planar to cylindrical orientation introduces an additional energy barrier, dominating nucleation kinetics at high De . Morphologically, crystallization is further modulated by entanglement and cluster crowding, with higher De increasing cluster density and reducing stem length. These findings highlight the critical role of orientation anisotropy in SIC under multiaxial deformation, offering a new insight in stretch-induced crystallization.