The adsorption of low molecular weight poly-(acrylic acid) (PAA) from aqueous solutions on TiO2 (anatase) has been studied and at pH 10 as a function of the electrolyte type and concentration. At low pH an exothermic heat of adsorption is found but at high pH in CaCl2 and NaCl solutions heat is consumed during adsorption. This endothermic effect is related to specific interactions between the cations and the TiO2 surface. If a Ca-salt is used the endothermic effect also originates from Ca2+ PAA interactions. The most likely driving force for PAA adsorption on TiO2 at high pH is the entropy gain by the release of hydration water of specifically interacting ions. (C) 1994 Academic Press, Inc.