Effect of Film Thickness on Morphological Evolution in Dewetting and Crystallization of Polystyrene/Poly(ε-caprolactone) Blend Films

In this Article, the morphological evolution in the blend thin film of polystyrene (PS)/poly(e-caprolactone) (PCL) was investigated via mainly AFM. It was found that an enriched two-layer structure with PS at the upper layer and PCL at the bottom layer was formed during spinning coating. By changing the solution concentration, different kinds of crystal morphologies, such as finger-like, dendritic, and spherulitic-like, could be obtained at the bottom PCL layer. These different initial states led to the morphological evolution processes to be quite different from each other, so the phase separation, dewetting, and crystalline morphology of PS/PCL blend films as a function of time were studied. It was interesting to find that the morphological evolution of PS at the upper layer was largely dependent on the film thickness. For the ultrathin (15 nm) blend film, a liquid–solid/liquid–liquid dewetting–wetting process was observed, forming ribbons that rupture into discrete circular PS islands on voronoi finger...