CALORIMETRIC INVESTIGATIONS ON THE EFFECT OF POSITION OF FUNCTIONAL-GROUPS ON SURFACTANT ADSORPTION

The effect of the positions of sulfonate and of methyl groups on the aromatic ring of isometrically pure alkylxylenesulfonates on their adsorption investigated in this study using microcalorimetry and electrokinetic measurements is found to be marked. It was observed that the position of the sulfonate with respect to the alkyl chain is more critical than that of the methyl groups in determining the adsorption behavior. The surfactant with the sulfonate in the para position with respect to the alkyl chain adsorbed more than that with the sulfonate in the meta position. Steric constraint to the packing of the molecules is proposed to be the main reason for the differences in the adsorption of these surfactants. Zeta potential measurements showed no difference in the charge characteristics of the surfactants. Calorimetric results suggest enthalpy to be the main driving force for adsorption at low surfactant concentrations while the adsorption is entropy driven at higher surfactant concentrations. © 1993 Academic Press, Inc.