Wettability improvement of bacterial polyhydroxyalkanoates via ion implantation

Water wettability of polyhydroxyalkanoates (PHAs), which were produced by bacteria, were improved by carboxyl ion implantation. Ion implantation was performed at an energy of 150 keV with fluences ranging from 5×1012 to 1×1015 ions/cm2. The surface properties were characterized by means of contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Similar contact angle changes were observed on polyhydroxybutyrate (PHB) and poly (hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx). For PHB, the contact angle of water decreased from the original 68.5° to zero at the fluence of 1×1015 ions/cm2. For PHBHHx, it decreased from 91.5° to 68.5°. The results revealed that ion implantation improved water wettability of the PHAs. Furthermore, it was found that the intensities of three components CC, CO and CO, which were resolved from the C1s spectra for pristine PHAs, decreased after the COOH+ implantation. Notably, a new component at 284.6 eV, which corresponds to the amorphous carbon structure, appeared after implantation. The present study suggests that the improvement of water wettability of the PHAs might come from the destruction of original surface chemical bonds and formation of an amorphous carbon phase by ion implantation. The influence of surface morphology on wettability is also discussed.