PROBLEM OF MEASURING STERIC INTERACTION FORCES BETWEEN SURFACES BEARING ADSORBED LAYERS OF MACROMOLECULES IN GOOD SOLVENTS

Several new techniques based on the use of a magnetoelectric dynamometer are described. The dynamometer can be used to measure an adhesion force f(a)(*) (with a precision of +/- 5 nN) between two fluid particles (heptane drops or air bubbles) of radius R approximate to 1 mm and between two curved mica sheets in polymer solutions, as well as a thinning rate dH(f)/dt of microscopic liquid films between two mica surfaces and two liquid particles bearing a load of a constant joining force f(p) in a film thickness range H-f less than or similar to 1 mu m. Use was made of poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA) and acrylic acid-vinyl acetate copolymers (CP) in aqueous electrolyte solutions which are good solvents for these polymers. Attention was paid to the problem of measurement of adhesion forces between surfaces bearing adsorption layers of polymers in good solvents, in order to explain a possible evolution of the system of two interacting adsorption layers from 'restricted' to 'full' equilibrium during a pull-off process.