Effects of Time and Compression on the Interactions of Adsorbed Polystyrene Layers in a Near-ϑ Solvent

Abstract

We have investigated the effects of molecular weight, adsorption time, force-measuring rate, and repeated compression−decompression cycles (previous history) on the interactions between high molecular weight polystyrenes adsorbed on mica from dilute cyclopentane solutions under near-ϑ solvent conditions. On the first slow approach, a long-range bridging attraction, which needs several minutes to fully develop for each incremental movement of the surfaces, is found at separations below 6Rg. The interaction becomes a steep hard-wall repulsion at separations below 0.5Rg. With increasing molecular weight the thickness of the adsorbed layers increases, and the attractive bridging force on approach and adhesion on separation decreases. Self-consistent field theory underestimates the onset location and depth of the attractive minima but accurately predicts the location of the hard-wall repulsion. For shorter (nonequilibrium) adsorption times, the bridging attraction and adhesion are stronger and occur at smaller...