Randy D. Hazlett

Fractal applications: Wettability and contact angle

Abstract A theromodynamic expression is derived fro the equilibrium contact angle on fractal surfaces in which the welted surface area is a function of the contacting fluid. The correlation for fractal surfaces can be decomposed into an areal contribution analogous to Wenzels roughness ratio, which alway enhances the natural wettability characteristics of the material, and a wettability alteration factor due to fluid adsorbate size differences. Reported fractal properties of reservoir materials suggest that for most fluid pairs, such porous media will appear perfectly wetted by one of the fluids. Fractional and mixed wettability states are not prohibited by the theory but exist as combinations of perfectly wetting and perfectly nonwetting domains.

Stability of macroemulsions

Abstract The rupture of the thin films separating emulsion droplets has long been considered to be triggered by the long-range, attractive van der Waals forces; however, this study conducted in a shearfield coalescer shows that systems containing surfactant may, in some cases, yield trends contrary to predictions based on this hypothesis. These trends can be understood in terms of a new mechanism leading to film rupture which is called here percolation-enhanced coalescence. Those regimes in which this new mechanism dominates can be determined based on simple equilibrium phase behavior studies of the surfactant, oil, and water mixtures using the percolation model proposed here.

Droplet coalescence near liquid/liquid critical points

Abstract The state of matter within a fluid layer near a critical point differs profoundly in many aspects from states further removed from the critical point. The interfacial tension tends to vanish, the interface thickens, and long-range concentration fluctuations exist. Because of these effects, critical phenomena have been investigated as possible sources of instability in thin films. Shear-field coalescence studies have been performed between phases of a simple ternary system containing no surfactant as a function of distance from a critical point. The coalescence efficiency was measured as a function of temperature through time dependent photomicrographic analysis of emulsion samples within a shear-field coalescence cell. The apparatus, procedure, and analysis are outlined. No evidence was found for the promotion of coalescence by critical phenomena for values of reduced temperature, T r = ( T − T c )/ T c , down to 4×10 −4 .