Local phase separation at the growth front of a polymer spherulite during crystallization and nonlinear spherulitic growth in a polymer mixture with a phase diagram

Local phase separation at the growth front of a spherulite has been found during crystallization in a polymer mixture of poly({ε}-caprolactone) and polystyrene. The phenomenon can be qualitatively explained by the coupling between the preferential rejection of impurities (polystyrene) during crystallization and the existence of a phase diagram. This unusual phase separation clearly shows that there is an impurity-rich layer on the growth front of the spherulite. A nonlinear growth of spherulite and a shape instability have also been found in this system. They are discussed on the basis of the formation of an impurity-rich layer at the growing interface. We also discuss the relation between our results on spherulitic growth and the current theories on dense branching morphology in diffusion-controlled growth.