Morphogenesis and non-equilibrium pattern formation in two-dimensional polymer crystallization

Abstract

Polymer crystallization is discussed in the context of nonequilibrium structure formation. In particular, we focus on the morphogenesis of polymer crystals during growth and annealing processes. We combine observations on quasi-two-dimensional polymer films, mainly obtained with atomic force microscopy, with computer simulations using a generic algorithm for growth and reorganization in two-dimensional ordering processes. Because of the simplicity of the simulation model, we are able to explain many properties of growth, morphogenesis, and melting of polymer crystals. In particular, we show that melting in polymer crystals is preceded by reorganization processes and the stability of the polymer crystal is not directly related to the structures formed immediately after crystallization. In our simulations, we identify and systematically investigate some morphological phases which are observed under various conditions of growth and annealing such as edge-thickening of crystals, hole-rim patterns, and a droplet phase. The simulations allow for the determination of some nonequilibrium properties such as the internal energy and the nonequilibrium heat capacity. We show that multiple-peak melting endotherms result from morphogenetic transformations and we scrutinize some widely used concepts such as melting-recrystallization phenomena.