Polymer-surfactant interactions: an ultrasonic relaxation study.

Polymer-surfactant interactions in water-poly(vinylpyrrolidone)-Na dodecyl sulfate systems have been investigated, at 25°, by ultrasonic relaxation methods as a function of polymer and surfactant concn. At fixed polymer content, three regions, characterized by significant differences in their kinetic behavior, have been obsd. In the first region the relaxation time increases with the surfactant content, in the second it is nearly const., and in the third region it decreases with increasing surfactant concn. Such behavior has been ascribed to the binding of the surfactant aggregates on the polymer backbone and to micelle formation above the satn. threshold. To account for the reported behavior, a kinetic model has been developed from the theory of ultrasonic relaxation in micellar solns. Some thermodn. quantities related to polymer-surfactant interactions, i.e. the Gibbs energy of binding per monomer, ΔGbind/〈m〉, where 〈m〉 is the no. of monomers in polymer-bound micelles, and the vol. change of binding of the surfactant to the polymer, ΔVbind, have been obtained from the data anal.