Long-range attractive forces between two mica surfaces in an aqueous polymer solution

Abstract

High polymers are widely used as flocculants in aqueous colloidal dispersions^1,2. All direct investigations to date of the forces between surfaces bearing adsorbed polymers in good solvent media, however, have indicated a monotonically increasing repulsion, rather than attraction, as the surfaces approached^3–8. We have now measured the interactions between two smooth mica surfaces immersed in an aqueous solution of polyethylene oxide (a good solvent system) in the range 0–300 nm apart, and find that at low adsorbance of the polymer on the mica there is a reversible, time-independent, long-range (∼2.5 R_g, the unperturbed radius of gyration of the polymer) attraction as the surfaces approach. On permitting equilibrium adsorption of the polymer to take place, the attraction disappears, to be replaced by monotonically increasing, long-range repulsion.