Morphological change of self-organized protrusions of fluoropolymer surface by ion beam irradiation.

Polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP) are typical fluoropolymers displaying several desirable technological properties such as electrical insulation and high chemical resistance. When their surfaces are irradiated with ion beams, dense micro-protrusions formed after the emergence and spread of micropores across the entire irradiated area, allowing culture cells to spread on the top of the protrusions. In this study, we investigate the morphological changes introduced in the fluoropolymer surfaces by ion beams as the energy of the beams is increased. When an FEP sample was irradiated with a nitrogen ion beam with an energy of less than 350keV at 1.0μA/cm2, protrusions were formed with a density between 2×107/cm2 and 2×108/cm2. However, at energies higher than 350keV, the protrusions became sparse, and the density dropped to 5×102/cm2. Protrusions appeared sporadically during irradiation at high energies, and the top of the protrusions appeared as spots inside the sample, which were difficult to etch and became elongated as the erosion of the surface progressed. Erosion was caused by sputtering of FEP molecules and evaporation at notably elevated temperatures on the surface. Analysis based on attenuated total reflectance/Fourier transform infrared spectroscopy showed the presence of C C bonds as well as –COOH, –C O, and –OH bonds on all irradiated samples. Their concentration on the surface densely covered with micro-protrusions was higher than that on the surface with sparse protrusions after irradiation at energies exceeding 350keV. Thus, we determined a suitable range for the ion energy for creating FEP surfaces densely covered with protrusions. [ABSTRACT FROM AUTHOR]