EXPERIMENTAL INVESTIGATIONS OF THE INTERACTION FORCES IN CONCENTRATEDDISPERSIONS

Currently there are no techniques which enable one to measure directly the interaction energy between two colloidal particles. However, one can get a handle on the particle interaction profile either by measuri ng the interactions between macroscopic surfaces or by measuring some bulk property of a colloidal dispersion from which the interparticle f orce can be calculated. In this paper we have used both of these techn iques on similar systems for comparison. We have chosen to measure the steric interaction between (1) layers of poly(vinyl alcohol) (PVA) an d (2) layers of a comb copolymer of poly(methyl methacrylate)/poly(eth ylene oxide). The forces of interaction for layers of these two polyme rs adsorbed on mica were measured using the surface forces apparatus. In both cases a long-ranged repulsive interaction was observed; this c ommenced at a surface separation of some 150 nm for the PVA and 25 nm for the comb copolymer. The same polymers were then adsorbed to poly(s tyrene) latex particles and the osmotic pressures of the latices measu red as a function of their volume fraction. From the volume fraction o f the latex the average separation between the particles could be calc ulated, and the interaction energy could be calculated from the osmoti c pressure data. Qualitatively similar results for the two techniques were found and quantitatively the results were in agreement to within an order of magnitude.