Thermodynamics of interaction between sodium bis(2-ethylhexyl) sulfosuccinae and polymers in aqueous solutions by isothermal titration microcalorimetry

nonionic water-soluble polymers, including polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) have been investigated by using isothermal titration microcalorimetry in aqueous solutions at 298.15 K. The results show that the critical aggregation concentration, which corresponding to the first turning point in the curve of experimental interaction heat versus concentration of the surfactant, is lower than the critical micellar concentration (cmc), confirming the existence of polymer-surfactant interactions. The value of cac is not sensitive to the relative amount of polymer in low concentration range of the polymer. The mono-layer saturated adsorption concentration, which corresponding to the second turning point, rises as the polymer concentration is increased. The interaction between PVP and AOT is stronger than that between PEG and AOT. The results also indicate that the aggregation of AOT in water and polymers solutions is entropically driven. The observed thermal effects have been interpreted in terms of the interactions of the polymer molecules with AOT monomers or the molecular clusters. (c) 2005 Wiley Periodicals, Inc.