Studies on confined crystallization behavior of polycaprolactone thin films

The confined crystallization behavior of polycaprolactone (PCL) in thin and ultrathin films was studied by AFM (atomic force microscopy). It was found that the crystalline morphology of PCL depended on the film’s thickness. When the thickness is d > 2 Rg (radius of gyration), the polymer can crystallize into spherulites; when Rg < d < 2 Rg, a dense-branch morphology and dendrites could be found; when d < Rg, an “islands” structure could be obtained. Moreover, the effects of the crystallization temperature and the substrate and the molecular weight on the crystalline morphology were discussed. It was shown that the crystallization of PCL in thin films is a diffusion-controlled process, and it can be explained by diffusion-limited aggregation.