The use of XPS and labelling techniques to study the surface chemistry of carbon fibres

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Abstract
A technique has been developed for the chemical analysis of carbon-fibre surfaces. This is based upon the labelling of acidic COOH groups, with barium Ba2+ for X-ray photo-electron spectroscopy (XPS). The technique provides a quantification of the surface concentrations of oxygen atoms and acid groups and has demonstrated the general chemisorptive ability of the fibre surface. It is shown that a saturation level exists for oxygen present as functional groups, which is approximately equal to 6000 atoms per (10 nm)2 unit surface area, for both Type I and II fibres. However, the maximum unit area concentrations of acid groups are 550 (Type I) and 1900 (Type II), as a result of oxidative surface treatments. Oxidation of Type I samples results in an approximately threefold increase in chemisorptive power. The overall picture of surface chemistry which emerges is important to an understanding of the true and complex nature of the adhesive interfacial bond, between the fibre and resin matrix, in a composite material.