FORCES BETWEEN LIQUID INTERFACES IN THE PRESENCE OF POLYMER - CONCENTRATION, SOLVENT, AND MASS EFFECTS

We report surface force measurements; between emulsion droplets and fl at air-water interfaces (foam films) in the presence of an aqueous sta tistical copolymer solution (of poly(vinyl alcohol) and poly(vinyl ace tate)) in the dilute regime. We observe a repulsive force that is expo nentially decaying and that cannot be attributed to electrostatic doub le-layer repulsion. The qualitative behavior of the repulsive force we akly depends on the polymer concentration, while its range is a functi on of the polymer average molecular weight that is varied from 10 000 to 155 000. The force is drastically affected when the temperature app roaches the Theta point (going from gl,od to Theta conditions). We sho w that the force range scales as the polymer coil radius of gyration. These results are compared with theoretical predictions.