Measurement of the interaction between adsorbed polyelectrolytes

Abstract

Direct measurements of the force between layers of gelatin adsorbed on mica surfaces have been carried out. Gelatin adsorbs on mica surfaces both above and below its isoelectric point (pH = 5). At pH's below the isoelectric point the gelatin appears to adsorb in a flat configuration, whereas at pH's above the isoelectric point the adsorbed polymer assumes a more extended conformation, and the steric interactions are of longer range. The effect of electrolytes on measured forces is different for different pH values, because the nature of the electrostatic interaction between the surface and the gelatin and between gelatin segments changes as the pH is varied with respect to the isoelectric point. The adhesion measured upon separation of the surfaces shows a maximum at the isoelectric point. It is concluded that the adsorption of gelatin and the range of the interactions are governed by the relative magnitude of electrostatic surface-segment and segment-segment interactions. The results can be interpreted by describing the structure of the adsorbed layer using a 'three-layer model' originally proposed by W. Norde and J. Lyklema (1978). Show more