Determination of the acidity of carbon-fibre surfaces by means of X-ray photoelectron spectroscopy adsorption isotherms

Abstract

The acidity of carbon fibres before and after an electrolytic surface treatment has been investigated by means of a novel method, adopting adsorption isotherms to interpret the uptake of labelling ions from solution. X-Ray photoelectron spectroscopy (XPS) can measure the amount of ions taken up directly so that gas adsorption isotherms can be applied and a monolayer coverage calculated. This can be converted to a measure of the number of acidic groups on the surface available for bonding. For the particular fibre tested, the fibre acidity increased with surface treatment up to the optimum adhesion level determined previously by single-fibre fragmentation tests. Additional information on bonding has been obtained from the form of the isotherms and consideration of the heat of adsorption determined from them, as well as chemical information obtained by measurement of the Auger parameters of the adsorbing ions.