Surface Energy Analysis of Treated Graphite Fibers

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Abstract
Wettability measurements and surface energy analysis are applied to isolate the (London-d) and (Keesom-p) polar contributions to solid-vapor surface tension γsv=γd sv + γp sv of surface treated graphite fibers. Surface treatments include metal coatings with Al, Cu, and Ni, chemically reducing heat treatments in H2 and vacuum, and films of highly chlorinated polymers such as polyhexachlorobutadiene and polychloral. This study shows that the highly polar surface properties γp sv|γsv ≃ γd sv|γsv ≃ 0.50 of commercial graphite fibers can be modified by surface treatment to display dominant dispersion character with γd sv|γsv ≃ 0.79 to 0.92 without substantial reduction in total surface energy γsv. For adsorption bonded fiber/matrix interfaces a new method of mapping the surface energy effects of an immersion phase upon the Griffith fracture energy γG is applied to define criteria for strong interfacial bonding under both air and water immersion.