THE KINETICS OF DISPLACEMENT WETTING IN LIQUID LIQUID SOLID SYSTEMS

Spontaneous displacement wetting, where a drop of one liquid displaces a second immiscible liquid from a smooth solid surface, has been investigated experimentally. Relationships between dynamic advancing contact angle and displacement velocity were established for systems of widely ranging viscosity ratio. The experiments were interpreted by extending a previously established correlation for liquid/vapor systems, as well as via a comparison with the hydrodynamic theory of Cox (J. Fluid Mech. 168, 169 (1986)). To compare experimental data with the hydrodynamic theory, a parameter which was unknown a priori-the ratio of slip length to macroscopic length scale-had to be estimated. Consequently, the relationships between displacement kinetics and material properties of the liquids (viscosities, interfacial tension) and the solid (equilibrium contact angle) were shown to depend on the microscopic dynamics, which were in turn characterized by a degree of uncertainty. Nonetheless, by estimating the ratios of slip lengths to macroscopic length scales, it was possible to obtain a reasonable theoretical description for experimental systems of widely ranging viscosity ratio. © 1990.