Lewis acid/base interactions were shown to play an important role in the optimization of the interfacial adhesion of reinforcing carbon fibers to thermoplastic polymer matrices. Inverse gas chromatography (IGC) and x-ray photoelectron spectroscopy (XPS) were used to characterize the acid/base nature of the carbon fiber surfaces. Capillary column IGC (CIGC) was used to determine the acid/base nature of thermoplastic polymer surfaces. To quantify the non-dispersive (acid/base) interactions, the dispersive component had to be factored out by separate experiments. The carbon fibers (both surface pretreated and untreated) were found to be predominantly acidic while the polymer matrices (polysulfone, polycarbonate, and polyetherimide) exhibited basic properties. Single fiber fracture tests showed that increased acidity in the fiber surfaces (as a result of surface pretreatment) resulted in a significant improvement in the interfacial adhesion to the basic polymers. The acid/base interactions, however, were not solely responsible for the most favorable adhesion. The dispersive component and thus, the carbon fiber structure also played a role. / Master of Science