FORCES BETWEEN SOLID-SURFACES IN BINARY-SOLUTIONS

Experimental measurements of the solvation forces between mica surfaces immersed in a binary solution of octamethylcyclotetrasiloxane and cyclohexane are reported. At all bulk concentrations examined (0-14, 32 and 42 mol% cyclohexane), the force varies between attraction and repulsion as the surface separation is decreased. The magnitudes of the forces at the attractive force minima decay exponentially with surface separation. The characteristic decay length and the average separation between attractive minima are functions of the bulk concentration. The statistical mechanics of inhomogeneous one-dimensional hard rod mixtures can be used to interpret the experimental results. The distribution functions and thermodynamic properties of a multicomponent hard rod fluid confined in a one-dimensional slit-pore are summarized. Density profiles and disjoining pressures are calculated as functions of pore width. Because of mechanical instabilities associated with the force measurement technique as presently used, not all theoretically predicted force minima (and maxima) are experimentally accessible.