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Abstract
The surface free energy (γ s ) of modified carbon fibers was determined by tensiometry and effects of CF4-O2 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, γ 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 γ P S values decreased to almost zero and the dispersive component became about 18 mJ/m2. 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.