Photoetching and modification of poly(tetrafluoroethylene-co-hexafluoropropylene) polymer surfaces with vacuum UV radiation

Abstract

Films of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) were exposed to radiation from 6.7 x 104 Pa He and Ar dc arc plasmas that were made to rotate inside of a graphite tube by the application of an auxiliary magnetic field. The films were covered with optical filters having different cut-off wavelengths to vary the vacuum ultraviolet (VUV) radiation that modified the fluoropolymer surface. With arc currents of 7 A and sample temperatures up to 110 oC, the photoetch rate of FEP was ca. 50% higher than for PTFE. Consistent with results for PTFE, treated FEP showed the following: (1) contact angles that started to decrease in the wavelength region between 173 and 160 nm and continued to decrease with shorter wavelengths; (2) surface roughening; (3) defluorination of the surface with a slight increase in the atomic%C and formation of C-C bonds in the top 3-5 nm of the surface as detected by XPS analysis; and (4) incorporation of oxygen, presumably from reaction with oxygen in air.