Systematic Kinetic Analysis on Monolayer Lamellar Crystal Thickening via Chain-Sliding Diffusion of Polymers

Abstract

Lamellar polymer crystals are metastable due to their limited lamellar thickness. We performed dynamic Monte Carlo simulations of lattice linear polymers to investigate the kinetics of isothermal thickening via chain-sliding diffusion in single lamellar crystals of polyethylene and poly(ethylene oxide). We sorted out three typical cases for controversial experimental observations. The basic case is a continuous increase of lamellar thickness for heavily folded long chains, with a logarithmic time dependence typical at the lateral growth front. Its kinetics is dominated by the activation energy barrier for sliding diffusion with higher speeds at higher temperatures. For integer-folded short chains, however, the lamellar thickness increases discontinuously, and its kinetics is dominated by a free energy barrier for surface nucleation. The latter can be further split into two cases: the thickening in the melt is mainly driven by the bulk free energy, with lower speeds at higher temperatures due to a temperature-sensitive barrier; while the thickening on a solid substrate is mainly driven by the surface free energy, with higher speeds at higher temperatures due to a temperature-insensitive barrier. The simulations facilitate our systematic understanding to the case-by-case microscopic mechanisms for the thickening of monolayer lamellar crystals via sliding diffusion of polymers.