Controlling drop coalescence using nano-engineered surfaces

Abstract

The dynamics of drop coalescence are explored on micro-scale surface features for the first time. Drop coalescence is defined as a process by which two or more droplets, bubbles or particles merge during contact to form a single droplet, bubble or particle. There are two regimes that limit the dynamics of drop coalescence of a liquid. The first is regime is limited by the viscosity of the droplets. The second regime is limited by inertial forces caused by the motion that merges the two droplets. Currently, much work has been done to study drop coalescence in a liquid-liquid environment and the phenomenon has been well defined and modeled. Previous work has been done to understand liquid-liquid drop coalescence using liquids with varying viscosity, but the effects of solid micro-textured surfaces on drop coalescence dynamics of low density liquids, such as water, have not yet been analyzed and quantified. Very little has been studied about drop coalescence in a solid-liquid-air interface. In this thesis, drop coalescence in its inertial regime will be defined in low viscosity liquid, water, on surfaces with varying wettability and micro-scale features. Surfaces include microstructures consisting of a regular array of square posts defined by the aspect ratio of the posts and the spacing between the posts. This work focuses on the development of a fundamental understanding and physical model of micro-scale surface texture effects on drop coalescence to provide aid in future surface design applications. These applications could allow for the controlling of this phenomenon to promote drop-wise condensation in order to increase efficiencies of condensers or to aid in water-oil separation procedures.