Poly(3-hydroxybutyrate-co-10%3-hydroxyhexanoate)(PHBHHx) thin films were prepared by means of spin-coating PHBHHx/chloroform solutions on the silicon substrate. The crystalline morphologies of PHBHHx thin films were observed by atomic force microscopy(AFM) at room temperature. A novel crystalline morphology, that is like sunflower was found when the film is very thin and named as sunflower-like crystalline morphology. Compared with usual PHBHHx spherulites, there are obvious differences in aspects of nucleation, crystal growth process and crystalline morphology for the sunflowers. The PHBHHx/chloroform solution properties and the substrate have great effects on the formation of the sunflower. A circular boundary that may result from a liquid-liquid phase separation in PHBHHx solution first formed in the thin film during the spin-coating process, then it induced the formation of the sunflowers.
On polyhydroxybutyrate banded spherulites, concentric rings were observed between cross polarizers or without polarizers. The rings used to be considered as cracks. In this paper, we provide evidences to distinguish the concentric rings from cracks observed on PHB spherulites. Furthermore, atomic force microscopy confirmed that these concentric rings with varying spacing were growth terraces rather than cracks. The height of the terraces reached up to several hundred nanometers. It was observed that the external terraces were higher than the internal terraces, which was proposed to result from layer by layer growth. This is the first report on the new microscopic feature of polyhydroxybutyrate spherulites. Spherulites with birefringent bands, wavy fluctuation of height were also observed.
