Band-to-Nonband Transition into Unique Poly(ε-caprolactone) Crystals by Modulating the Interplay of Diffusion and Growth

Previously, by modulating the interplay of chain diffusion and crystal growth rate in evaporating solution-cast poly(epsilon-caprolactone) (PCL) thin films, discrete banded crystals were obtained when diffusion and growth are competitive. In this study, we further investigated the effect of diffusion and growth, here mainly the growth rate on the crystallization of PCL. We found that there is a threshold (or range of) growth rate above which the banding cannot develop, and thus a band-to-nonband transition leads to the emergence of a novel crystal pattern. Accompanied by the band-to-nonband transition, the lamellar orientation also changes from flat-on to mainly tilted or even edge-on. The result reveals the significant impact of the diffusion and growth, especially the growth rate on the crystal construction and then the crystal morphology.