Thermodynamic studies of interaction between cationic surfactants and polyvinyl pyrrolidone using potentiometric techniques

The interaction between a homologous series of n-alkyl trimethyl ammonium bromides and polyvinyl pyrrolidone was studied by a potentiometric method using a surfactant-selective electrode. The binding isotherms were measured for different conditions and show a concentration dependence attributable to aggregation of the polymer-surfactant complexes. The binding isotherms are discussed in terms of the binding potential concept of Wyman and are used to calculate an apparent Gibbs energy of binding per surfactant cation. The binding isotherms show that the C-1 decreases with increasing chain length of surfactant. The degree of dissociation of the counterion and thermodynamic parameters such as Delta H-v (enthalpy of binding) and Delta S-v (enrropy of binding) were calculated. (C) 1998 Elsevier Science B.V. All rights reserved.