Kinetics of post-treatment structural transformations of nitrogen plasma ion immersion implanted polystyrene

The surface chemistry of a synthetic material in contact with a biological system has a strong influence on the adhesion of proteins to the surface of the material and requires careful consideration in biomedical applications. The structure of plasma immersion ion implantation (PIII) treated polymer and its surface free energy depend on the ion fluence delivered during the treatment and on the time after the PIII treatment. These dependences have been investigated using the example of nitrogen plasma implanted polystyrene (PS). Contact angle measurements, FTIR–ATR spectra and X-ray photoelectron (XPS) spectra were acquired as a function of ion fluence and time after treatment. The results showed a close relationship to the kinetics of free radicals that had been examined in a previous study. The kinetics of oxidation and surface free energy had two stages, one with a characteristic time of several hours and the other with a characteristic time of several days. The concentration of nitrogen-containing groups decreased with time after PIII treatment, partly, due to their release from the PS surface.