INVESTIGATION OF THE INTERACTION FORCES OF POLYMER-COATED SURFACES USING FORCE BALANCE, RHEOLOGY, AND OSMOTIC-PRESSURE RESULTS

The forces between layers of poly(methyl methacrylate)/poly(12-hydroxystearic acid) comb copolymer adsorbed on macroscopic (mica) surfaces have been measured. Results show that the interaction energy increases monotonically and approximately exponentially with decreasing surface separation, with the force commencing at a surface separation of approximately 24 nm. Comparisons have been made with rheological and osmotic pressure data for latices stabilized by adsorbed layers of the same copolymer taken from the literature. The osmotic pressure data agree reasonably closely with the macroscopically measured forces, although due to the increased sensitivity of the surface forces apparatus, a softer, longer range interaction was observed. The general form of the rheological data is similar to the results obtained in the surface force experiments; however, the elastic moduli predicted from the force data are more than an order of magnitude greater than those experimentally determined. This implies that the models used to make the comparison do not hold at the high volume fractions used.