Dynamic and thermodynamic aspects of polymer-surfactant interactions. The SDS-PVP-water system.

The water-PVP (polyvinylpyrrolidone)-SDS (sodium dodecylsulfate) system was investigated by ultrasonic relaxation measurements. In water-PVP mixts. the relaxation time is independent on the polymer content, whereas in water-SDS solns. it decreases on increasing the amt. of surfactant in micellar form. In the ternary water-PVP-SDS systems, at fixed PVP content, 3 different regions were obsd. on increasing the amt. of SDS: namely, at very low surfactant content the relaxation time, τ1, increases then remains nearly const. and finally decreases. The above behavior was ascribed to surfactant binding onto the polymer and to micelle formation, resp. By analyzing the dependence of relaxation time(s) on compn., it was possible to divide the investigated region in 3 domains (i.e. non-interaction region, polymer-surfactant interaction region, and micellar region). A phase diagram for the above system was drawn according to the exptl. kinetic results. From the data obtained by ultrasonic relaxation expts. the no. of SDS mols. bound to PVP, 〈m〉, was evaluated and the Gibbs energy of binding, [ΔGbind/〈m〉], calcd.