WETTABILITY AND SURFACE FREE-ENERGY OF ELECTROLYTICALLY OXIDIZED GRAPHITE FIBERS

Wettability of electrolytically oxidized graphite fibers has been inve stigated by contact angle measurements employing the Wilhelmy method. The atomic ratio of oxygen to carbon, O/C, in the surface layer of the graphite fiber increased with increasing electric specific charge. Co ntact angle hysteresis was not observed for the untreated graphite fib er (O/C = 0.01). The contact angles decreased with increasing O/C, esp ecially for the receding angle, and approached constant for O/C > 0.2. The nondispersive and dispersive surface free energies of the oxidize d graphite fibers were calculated from the experimentally determined c ontact angles. The nondispersive surface free energy increased by the oxidation, whereas the dispersive one decreased. From the results of s urface analysis, it was found that the changes in the nondispersive an d dispersive surface free energies were caused by the increase in O/C ratio and the decrease in surface crystallinity, respectively.