Crystallization of a polymer on a surface

TL;DR

This study investigates the structural transitions and free energy landscape of a semi-flexible lattice-polymer on a surface, revealing deviations from classical surface nucleation theory during early crystallization stages.

Contribution

It provides new insights into the crystallization process by showing that initial nuclei are more complex than previously assumed, affecting theoretical models.

Findings

Identification of two-dimensional crystal coexistence at low temperatures

Observation of a transition to disordered coil and three-dimensional structures with increasing temperature

Discovery of deviations from classical surface nucleation theory in early crystallization stages

Abstract

We have studied the structure and free energy landscape of a semi-flexible lattice-polymer in the presence of a surface. At low temperatures coexistence of two-dimensional integer-folded crystals is observed. As the temperature is increased there is a transition from these crystalline configurations to a disordered coil adsorbed onto the surface. The polymer then gradually develops three-dimensional character at higher temperatures. We compute the free energy as a function of increasing crystallinity and compare with the free energy profiles assumed by the Lauritizen-Hoffman surface nucleation theory of polymer crystallization. Our free energy profiles exhibit a `sawtooth' structure associated with the successive formation of chain folds. However, in the early stages of crystallization our profiles significantly deviate from those assumed by surface nucleation theory because the initial nucleus is not a single stem but two incomplete stems connected by a fold. This finding has significant implications for the theoretical description of polymer crystallization.