COLLOIDAL DISPERSIONS OF SILICA-CONTAINING PHYSISORBED BETA-CASEIN - A SOLVENT NMR RELAXATION STUDY

Spin-spin relaxation rate measurements have been performed on the solv ent in aqueous silica dispersions containing a physisorbed polyelectro lyte, the milk protein beta-casein. An enhancement in the relaxation r ate resulting from the adsorption of beta-casein at the silica interfa ce has been studied as a function of pH, protein concentration and ion ic strength. Adsorption occurred over a narrow pH range. The conventio nal adsorption isotherm was measured and allowed a ''bound fraction'' to be extracted from the relaxation rate data. With increasing ionic s trength, the adsorbed amount was found to increase.