Measurement of forces between two mica surfaces in aqueous poly(ethylene oxide) solutions

Abstract

WE have measured the forces between two curved mica surfaces immersed in a solution of 0.01% poly(ethylene oxide) (molecular weight 148,000) in 0.04 M MgSO₄ (a good solvent). The experimental technique allows the measureent of (1) forces as a function of surface separation; and (2) the refractive index of the medium between the surfaces^1,2. The forces exhibited large irreversibilities as well as short-term and long-term time dependent effects, and we conclude that—for observation times less than a few hours—these interactions cannot be described in terms of an equilibrium force law without specifying the previous history of approach of the surfaces.