Simulation of Polymer Crystal Growth with Various Morphologies Using a Phase-Field Model

A finite element-based phase-field model was developed to simulate crystal growth in semicrystalline polymers with various crystal morphologies. The original Kobayashi's phase-field model for solidification of pure materials was adopted to account for polymer crystallization. Evolution of a non-conserved phase-field variable was considered to track the interface between the melt and the crystalline phases. A local free energy density was used to account for the meta-stable states in polymer solidification. The developed model was successfully applied for simulation of two-dimensional (2D) polymer single- and polycrystalline morphologies (rectangular, orthorhombic, hexagonal, and spherulitic) in polypropylene and polystyrene (example in Fig.1). These morphologies were compared based on different supercooling and interface anisotropy. The results of simulated crystal morphology and growth rates were validated using experiments (example in Fig.2). The unique aspect of this work is that the employed model is capable of simulating multiple arbitrarily-oriented crystals and has no limitations with respect to the crystal morphology. The results show significant thermal effects on the shape and growth rate of polymer crystals.

Fig.1. 2D representations of a single spherulite growth of isotactic polypropylene crystal.

Fig.2. Optical microscope (OM) images of spherulites in isotactic polypropylene at

 (a) 100x and (b) 500x magnifications obtained with the Carl-ZeissŪ inverted OM in DIC mode.