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Micellar properties of sodium dodecyl sulfate (SDS) in aqueous mixtures of ethylene glycol (EG) were determined using techniques such as conductivity, density, EMF, surface tension, viscosity, ultrasonic velocity, and spectroscopy (fluorescence). The effective degree of disssociation of micelles ( a ) was determined using three different methods. Thermodynamics of micellization were obtained from the temperature dependence of critical micelle concentrations (cmc) values. The difference in Gibbs energies of micellization ( A G~) of SDS, between water and mixed solvent systems, was calculated to evaluate the influence of cosolvent on the micellization process. Surfactant aggregation numbers (N,) obtained from static fluorescence quenching methods indicated a decrease in the aggregation numbers with increasing concentration of ethylene glycol in the binary solvent mixtures. In addition, the micropolarity of the micellar interior was determined from the pyrene I,II:, ratios. These values were consistent with a decrease in the micropolarity surrounding the probe molecule as the EG content in the solvent mixture was increased.

The rheology of the air/water interface of mixed polymer/surfactant systems has been examined by the talc particle test. Polymer/surfactant pairs studied range from strongly interacting polyelectrolytes/ oppositely charged surfactant systems, such as sodium hyaluronate/alkyltrimethylammonium halides, carboxymethylcellulose/hexadecyltrimethylammonium chloride (HTAC), and an alternating copolymer of acrylamide and diallyldimethylammonium chloride (Merquat-550)/sodium dodecyl sulfate (SDS) to less strongly interacting systems of neutral polymers and charged surfactants, such as ethylhydroxyethyl cellulose/SDS or /HTAC, hydroxypropyl cellulose/SDS, poly(N-isopropylacrylamide)/SDS and poly-(Nvinylpyrrolidone)/SDS. Clear indications of surface viscoelasticity at the air/water interface were obtained over a wide range of compositions for several, but not all, polymer/surfactant pairs examined. These results extend our previous findings (Regismond, S. T. A.; Winnik, F. M.; Goddard, E. D. Colloids Surf., A 1996, 119, 221-228.) on mixed solutions of SDS and a cationic derivative of hydroxyethyl cellulose (polymer JR400). Generally, viscoelasticity provides evidence of a synergistic adsorption of the two components. Factors influencing the development of surface viscoelasticity are assessed.

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