Adsorption pattern of mixtures of trimethylammonium-modified hydroxyethylcellulose and sodium dodecyl sulfate at solid-liquid interfaces

We studied mixtures of aqueous solutions of cationic hydroxyethylcellulose JR400 polymer and anionic sodium dodecyl sulfate using dynamic light scattering and atomic force microscopy (AFM). A ternary phase diagram was established showing three interesting realms of the polymer-surfactant-water mixture: a preprecipitation area of lowered viscosity (polymer excess) compared to the pure polymer solution, a postprecipitation area (resolubilization at surfactant excess), and highly diluted samples with a stoichiometrical surfactant-polymer ratio close to that of maximum precipitation. Samples with various compositions representing these areas were imaged by atomic force microscopy on mica and on hydrophobically modified silica in contact mode. A correlation between light scattering data concerning particle size and, more important, structuring in the bulk on one hand and AFM images on the other hand was observed. It was revealed that the influence of surface properties is of less importance for adsorption, compared to the influence of the mixture in the bulk, provided that the mixture is prepared prior to adsorption.