|Abstract:||Lubricant-infused porous surfaces (SLIPS) demonstrate extreme liquid repellency such that a droplet immiscible with the lubricant can roll off at a very small tilt angle < 5°. There have been many applications in using SLIPS to achieve complex fluids handling, anti-fouling, self-cleaning, anti-icing, and enhanced condensation heat transfer. In recent studies of droplet dynamics on SLIPS, it was observed that a moving droplet on the lubricant film follows lubrication theory and the Landau-Levich law — there is a zone of capillary pressure-driven flow inside the lubricant wetting ridge around the droplet base when the capillary number is much smaller than one. The viscous dissipative force, which resists this capillary suction of lubricant, depends non-linearly on the capillary number with a two-thirds power.
This doctoral thesis focuses on the enhanced droplet transport on vibrating SLIPS, as well as the applications in anti-biofouling, enhanced self-cleaning and condensates heat transfer. To study oscillating droplets on SLIPS, we developed SLIPS that can be put in motion by a dielectric elastomer actuator (DEA). This system demonstrates its ability to generate tunable surface wettability that can precisely control droplet dynamics, from complete pinning to fast sliding, and even more complex motions such as droplet oscillation, jetting and mixing. Next, more detailed analysis of the synergistic effect among deforming droplet, lubricant film, and vibrating device on the fast sliding speed is discussed, in particular (i) transverse membrane velocity and resonant mode shapes of SLIPS membrane studied by laser vibrometer, and (ii) oscillatory droplet contact line dynamics studied by high-speed photography. Finally, we further demonstrate how vibrational actuation into SLIPS achieves enhanced condensate repellency and heat transfer compared to conventional repellent surfaces. Faster departing speed and smaller departing size of condensates on vibrating SLIPS were observed compared to non-vibrational SLIPS, which are crucial to enhance heat transfer during dropwise condensation. The time-averaged size distribution and temporal growth of condensates on this surface are experimentally analyzed. The roles of these unique behaviors on condensation dynamics are explained with the assist of a condensation heat transfer model.