(78g) Rates of Replacement of Initially Oil-Filled Microscopic Cavities with Bulk Water

We present experimental results and analysis for determining the rate at which initially oil-filled microcavities are replaced with bulk water and how factors such as viscosity, diffusion, density, and saturation affect this rate. While wetting phenomena has largely been explored for the liquid-gas-solid system, we investigated wetting phenomena in immiscible liquid-liquid-solid systems. Specifically, we investigated the factors affecting replacement rates of initially oil-filled microscopic cavities with water, undergoing a change from the Cassie-Baxter state (cavities fully-filled with oil and immersed in water) to the Wenzel state (cavities either partially emptied or completely emptied of oil, and instead filled with water) or from partially-water-filled to completely-water-filled (no oil remaining) Wenzel states. We fabricated cylindrical microscopic cavities in a silicon wafer, filled the cavities with various organic solvents dyed with fluorophores, then submerged the silicon wafers in water. Through fluorescence microscopy techniques, we observed the transition or replacement rates of the initially-oil-filled cavities with water in both oil-saturated and oil-absent water conditions. Among the factors we investigated, namely viscosity, density, surface chemistry, and diffusion (composed of solubility and diffusivity), diffusion dominated replacement rates. The rates for each of seven hydrocarbons we investigated were obtained by adapting 3P model after applying diffusion model. By using solvent-saturated water to minimized the effect of diffusion to the rates, the effect of other factors was investigated. We found a correlation between the surface tension and the rates of replacement. Understanding liquid-liquid-solid systems will open a new door in designing commercial and consumer products as well as broadening the scope of wetting phenomena.