Surface properties of oxyfluorinated PAN-based carbon fibers

In this study, the oxyfluorination of PAN-based carbon fibers was undertaken at room temperature using fluorine–oxygen mixtures, and the influence of oxyfluorination on properties such as wettability, surface polarity, surface free energy, conductivity and tensile strength was investigated. As the oxyfluorination time increased at a total pressure of 5 kPa, both the fluorine/carbon and oxygen/carbon ratios increased. The contribution of semicovalent C–F bond to F1s spectra is considerably decreased with increasing total pressure from 5 to 80 kPa, and at the same time, the contribution of covalent C–F bond is increased. As the total pressure of fluorine–oxygen mixtures increased, the contact angle of water significantly decreased and again increased to a similar value to that of as-received carbon fiber. A short oxyfluorination of carbon fibers considerably increased the wettability, that is, hydrophilicity. The electrical conductivity of oxyfluorinated carbon fiber is larger than that of the as-received fiber. This is because the surface region of carbon fiber is fluorinated. An increase in the tensile strength of about 18% after oxyfluorination is observed. The increase in tensile strength of oxyfluorinated carbon fibers can be understood as being due to a decrease in the diameter of the fiber.