Dependence of poly(3-hydroxybutyrate) crystal modifications on film thickness as revealed by reflection-absorption infrared spectroscopy

Thickness-dependent ultrathin films of poly(3-hydroxybutyrate) (PHB) were investigated by using infrared reflection-absorption spectroscopy (IRRAS). It was first found that the autogenetic β-form of PHB could be easily obtained through confining the film thickness under 20 nm at room temperature. Moreover, the interphase of PHB simultaneously exists with the β-form of PHB in the films with a thickness less than 10 nm. With the film thickness increasing from several nanometers to about 30 nm, the PHB molecules gradually carry out an orientation shift at the b-axis of PHB crystallite; simultaneously, for the α-form of PHB a conformational rearrangement probably takes place for the growth of helical crystal unit cells in the ultrathin films. The molecular structures and crystal evolutions at sub–100 nm were explained in detail by analyzing the corresponding IRRAS features.