Influence of Poly(vinylphenol) Sublayer on the Crystallization Behavior of Poly(3-hydroxybutyrate) Thin Films

The crystallization behavior of poly(3-hydroxybutyrate) (PHB) thin films on poly(vinylphenol) (PVPh) substrate was investigated by surface-sensitive grazing incident X-ray scattering and infrared reflection-absorption spectroscopy techniques. Compared with the crystallization of PHB on a Si wafer, the PVPh sublayer did not significantly affect the crystallization behavior of PHB in solution-cast samples, while significantly inhibited the melt crystallization of PHB. For films thinner than 175 nm, amorphous PHB was always fabricated irrespective of melt crystallization temperature. Only when the film thickness increased to 185 nm, the PHB started to crystallize at temperatures above 53 degrees C. The PHB crystals preferred to orient with the b-axes perpendicular to substrate. The inhibition of PHB melt crystallization was attributed to the thickness confinement and interdiffusion of PVPh and PHB, which caused a concentration gradient of PVPh in the PHB layer. From the thickness dependence of crystallization behavior, the PHB film can be divided into two layers: the inactive layer with high fraction of inter C=O and stable amorphous state; the interactive layer in which crystallization of PHB is sensitive to temperature. The existence of inactive layer accounts for the formation of crystals oriented with b-axes perpendicular to substrate.