Abstract
We perform kinetic Monte Carlo simulations of flow-induced nucleation in polymer melts with an algorithm that is tractable even at low undercooling. The configuration of the noncrystallized chains under flow is computed with a recent nonlinear tube model. Our simulations predict both enhanced nucleation and the growth of shish-like elongated nuclei for sufficiently fast flows. The simulations predict several experimental phenomena and theoretically justify a previously empirical result for the flow-enhanced nucleation rate. The simulations are highly pertinent to both the fundamental understanding and process modeling of flow-induced crystallization in polymer melts.
Highlights
Introduction.—The nucleation of microscopic crystallites in polymer liquids is profoundly influenced by flow [1,2]
A fundamental understanding of flow-induced crystallization (FIC) promises extensive control of polymer solid state properties, as virtually every property of practical interest is determined by the crystal morphology
The widely postulated mechanism for FIC states that flow forces the polymer chains into elongated configurations, which lowers the entropic penalty for crystallization [1]
Summary
Deformation of the amorphous chains has two effects on the nucleation kinetics: stretching reduces the entropic penalty for crystallization; and monomer alignment modifies the probability of compatible alignment with the nucleus. The change in elastic free energy ÁFel for chains with ensemble average constraints f 1⁄4 hrri, but locally at equilibrium, can be calculated by statistical mechanics [23]. An analytic calculation is not possible for finitely extensible chains, steep free energy gradients in. Week ending 11 SEPTEMBER 2009 highly stretched chains suppress fluctuations. Our numerical calculations for uniaxial deformations show that ÁFelðhrriÞ can be accurately approximated by an expression that interpolates between Gaussian elasticity [23] for small Trf and Cohen’s [22] approximation with r2 1⁄4 Trf at high stretching, ÁFel
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