Crystal Morphology of Poly(3-hydroxybutyrate) on Amorphous Poly(vinylphenol) Substrate

The crystalline morphology and orientation of poly(3-hydroxybutyrate) (PHB) thin film on the poly(vinylphenol) (PVPh) sublayer with different thickness was studied by atomic force microscopy, X-ray diffraction, and infrared spectroscopy. PVPh sublayer influences the morphology of PHB greatly. Although edge-on lamellae form on both Si and PVPh surfaces at relatively lower crystallization temperature, the morphology of them is quite different. It appears as sheaflike edge-on lamellar morphology on PVPh sublayer. In addition, the edge-on lamellae prefer to form on the PVPh sublayers at much higher crystallization temperature compared with that on Si wafer. The PVPh layer thickness also influences the crystalline morphology of PHB. On a 30 nm thick PVPh layer, sheaflike edge-on lamellae form in a wide range of crystallization temperatures. When the PVPh thickness increases to 65 nm, fingerlike morphology is observed when the crystallization temperature is lower than 95 °C. The fingerlike morphology is caused by a diffusion-limited aggregation process, and it requires an optimum condition. Thickness ratio between PHB and PVPh sublayer and temperature are two key factors for the formation of fingerlike morphology.