SURFACTANT AGGREGATION IN THE PRESENCE OF POLYMERS

A model for surfactant aggregation in the presence of macromolecules that involves the adsorption of micellar aggregates in the 'free space' of the coiled macromolecules is suggested. The model accounts for the interactions between macromolecules and surfactant molecules via the changes the former cause in the interfacial free energies between the hydrocarbon core of bound aggregates and the microenvironment and between the polar headgroups of the bound aggregates and the microenvironment. If the headgroup is sufficiently small, the overall surface free energy is decreased and thus aggregation is stimulated. Under such conditions, micelles which are bound to macromolecules form at a critical concentration which is smaller than the cmc for the formation of the free micelles. This model is able to explain the variety of experimental data which are available, particularly why surfactants with large headgroups do not stimulate the formation of bound micelles while those with sufficiently small headgroups do stimulate their formation. Calculations have been carried out for sodium dodecyl sulfate, Triton X-100 and dodecyltrimethylammonium chloride in the presence of poly(ethylene oxide).