Influence of oxygen plasma treatment of PAN-based carbon fibers on their electrokinetic and wetting properties

Oxygen plasma treatment was used to modify the surfaces of high-tenacity po lyacrylonitrile-based carbon fibers. Changes in the surface composition of plasma-treated fibers were investigated by electrokinetic (zeta-potential) measurements as well as by wetting studies to evaluate the solid surface te nsion. Treating carbon fibers in an oxygen plasma results in an increased s urface acidity, as can be seen from the overall shape of the zeta = f(pH) f unction and from the shift of the isoelectric points toward lower pH. The i ncreased surface polarity improves the wetting behavior versus water. Altho ugh the fibers become more hydrophilic, the adsorption of ions from the ele ctrolyte solution, which should compete with water adsorption, increases. A lmost no changes in the surface morphology could be monitored by scanning e lectron microscopy. However, wetting and zeta-potential measurements confir m changes at the fiber surface. zeta-Potential measurements and wetting (co ntact angle) measurements complement each other. This allows observation of changes taking place in the surface chemistry after modifications applied to industrially available unmodified carbon fibers. (C) 1999 Academic Press .