Ideal mixing of polymer-surfactant complexes of polyethylene oxide and sodium dodecyl sulfate plus sodium dodecanoate

Mixtures of the anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecanoate (SDoD) were investigated regarding their ability to bind to a hydrophilic nonionic polymer, polyethylene oxide (PEO). By electrical condu ctivity measurements, the parameters with respect to the onsets of surfacta nt aggregation were determined in the presence of 0.06 M PEO (critical aggr egation concentration) and in its absence (critical micelle concentration). It was found that both plots of these parameters for the multicomponent mi xtures against molar fraction of SDoD showed an ideal mixing behavior. The same technique was used to estimate the degree of ionization as a fundament al parameter relating to the interfacial composition of mixed aggregates. I n addition, in order to monitor changes in polymer-surfactant structures, w e used steady-state quenching fluorescence measurements to characterize the sizes of PEO-SDS/SDoD complexes at different compositions of the complex m ixture. (C) 1999 Academic Press.