Kinetic Monte Carlo simulations of the growth of polymer crystals

TL;DR

This paper uses kinetic Monte Carlo simulations to propose a new dynamic mechanism explaining why polymer crystal lamellae maintain a thickness near the thermodynamic minimum, contrasting with existing theories.

Contribution

It introduces a novel simulation-based mechanism showing how energetic costs constrain lamellar thickness to a stable value, differing from traditional models.

Findings

Crystal thickness converges to near l_{min} during growth

Energetic costs of extension and stem length constrain thickness

At small supercoolings, growth is inhibited by profile rounding

Abstract

Based upon kinetic Monte Carlo simulations of crystallization in a simple polymer model we present a new picture of the mechanism by which the thickness of lamellar polymer crystals is constrained to a value close to the minimum thermodynamically stable thickness, l_{min}. The free energetic costs of the polymer extending beyond the edges of the previous crystalline layer and of a stem being shorter than l_{min} provide upper and lower constraints on the length of stems in a new layer. Their combined effect is to cause the crystal thickness to converge dynamically to a value close to l_{min} where growth with constant thickness then occurs. This description contrasts with those given by the two dominant theoretical approaches. However, at small supercoolings the rounding of the crystal profile does inhibit growth as suggested in Sadler and Gilmer's entropic barrier model.