Measurement of forces between two mica surfaces in aqueous polyethylene oxide solution

Abstract

The force as a function of distance between two curved mica surfaces immersed in a solution of 0.01% polyethylene oxide (molecular weight 150,000) in 0.04 M MgSO4 (a good solvent) has been measured with precision by an interferometric technique. The most striking features of this study are the long-range nature of the interaction (i.e., many times the free coil diameter) and the marked hysteretic behavior. Our results indicate (1) the existence of a dilute long-range polymer layer forming on mica surfaces, probably possessing gel-like properties; (2) that even though the forces may be monotonically repulsive on approach, once significant overlap occurs there is sticking, probably through polymer bridging, resulting in effective adhesion; and (3) as the rate of segmental rearrangement toward equilibrium is very slow (> 1 hr) the effective forces between colloidal particles with adsorbed polymers of high molecular weight may often be determined by non-equilibrium relaxation mechanisms.