Characteristics of poly(vinylidene difluoride) modified by plasma-based ion implantation

Surface modification of polymers using radiation effects has been studied in a variety of fields, such as gas barrier or biochemical applications. However, the mechanism of improvement or degradation of polymers induced by radiation has not been well understood. In this study, poly(vinylidene difluoride) (PVDF) of crystalline phase of II (alpha form) was modified by plasma-based ion implantation (PBII) to control its adsorption properties for protein. Helium ions with applied bias voltages ranging from −1 to −20 kV were irradiated to the PVDF substrate for one minute and protein adsorption properties on the modified PVDF substrates was evaluated by the Western blotting method. As a result, adsorption of PVDF decreased with increasing the applied bias voltage, whereas the modification with only plasma treatment did not cause a significant change in adsorption properties for protein. The PBII-induced decrease in adsorption can be used for monitoring or patterning the protein. In order to study the mechanism, chemical and physical properties of the modified surfaces were analyzed with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) in attenuated total reflection (ATR) mode. Contact angles on the modified surfaces were also measured and surface free energies were calculated by Owens–Wendt–Rabel–Kaeble method. The surface morphology observed AFM and SEM did not show a significant change after the modification but the concentration of fluorine decreased and the surface energy on the surface increased after the modification. The influential factors in adsorption properties of the modified PVDF for protein are discussed.