Kinetic Monte Carlo Simulations of Anisotropic Nucleation in Polymer Melts Under Strong Flow.

Abstract

The tube model is the most established framework to describe the dynamics of entangled polymers under flow. Recent refinements of tube model have been verified against both bulk stress and neutron scattering measurements and these comparisons show that the model can accurately predict the configurations of polymer chains under strong flow[l, 2]. This effect of flow on chain configuration is believed to play a key role in the effect of flow on crystallisation in semi‐crystalline polymer melts. However, these models have not yet been used to provide insight into flow induced crystallisation. In this work, we present a scheme for computing the effect of molecular configuration under flow on anisotropic nucleation and growth of polymer crystals. We use a kinetic Monte Carlo algorithm to model the growth of polymer crystals, resulting in a computationally inexpensive model for polymer crystal nucleation. Changes in crystallisation kinetics due to molecular stretching and orientation are accounted for using the instantaneous molecular configuration under flow, which is computed using a tube model. The effect of flow on the orientation of polymer crystallites is also accounted for during the simulation, with the crystallites' orientational relaxation time depending on the crystallite size and aspect ratio. The simulation algorithm predicts the effect of bulk flow conditions and melt molecular weight distribution on both the nucleation rate and resulting crystal orientation.