Under Liquid Wetting Dynamics

Liquid drops wetting a surface kept in ambient air has been widely studied over the last few decades due to its manifold applications in technology and industry. However, for a surface kept submerged under-liquid, such wetting processes have been studied to a lesser extent. Understanding how a liquid drop interacts with a surface in the presence of another liquid medium is pivotal towards growing applications in marine ecosystem, environmental effects of oil-spills, advanced manufacturing techniques like immersion lithography, etc. It also poses the challenging issues of liquid-liquid displacement and contact line dynamics. The present study delineated some fundamentals of under-liquid wettability like coalescence of two sessile drops on an under-liquid substrate, spreading of liquid drops on an underliquid substrate and drop interaction with submerged micro-patterned substrates.Through relevant theoretical analysis as well as experimentation, it was found that the existing theories of drop interaction with a surface in air are inadequate when a surrounding liquid medium is considered, and needs to be modified bringing into effect key parameters of the surrounding medium, such as its density and viscosity. Consideration of a surrounding liquid medium also allows to provide a unifying framework to study such wetting processes. For coalescence and spreading, a universal behavior was observed in terms of the initial fast wetting regime inherent to such processes, and the notion of coalescence-spreading analogy was found acceptable to describe such phenomenon. However, for under-liquid wetting signature of micro-patterned substrates, a non-universal behavior was observed which indicates the need of newer theoretical approach to better understand wetting phenomenon on such under-liquid surfaces.