Wettability and Adhesion Characteristics of Plasma-Treated Carbon Fibers

The surface free energy (gamma (S)) of modified carbon fibers was determined by tensiometry and effects of CF4-O-2 plasma treatment were evaluated. The treatment with the gas mixture in which oxygen was above 40% accelerated preferentially the oxidation of fiber surfaces and the nondispersive component of the surface free energy, gamma (P)(S), increased to about three times that of the untreated fiber. On the other hand, the treatment with the gas containing CF4 above 80% induced fluorination and surface species such as - CF, - CF2, or - CF3 were formed. The gamma (P)(S) values decreased to almost zero and the dispersive component became about 18 mJ/m(2). The calculated work of adhesion between various fibers and the epoxy resin was well correlated with the interfacial shear strength of the composites formed with these materials.