Manipulating Liquid Volumes by Wettability-Patterned Substrates

The interaction of liquids with surfaces (both impervious and porous) is one of the most commonly observed phenomena in our daily life. Several studies exist that highlight both the fundamentals and applications of liquid impingement (both as droplets and high-flow-rate liquid jets) on surfaces. However, existing studies have almost all been in the area of impermeable substrates. The few studies that exist on the interaction of droplets (and not high-flow-rate liquid jets) with porous materials are on substrates of uniform wettability. On the other hand, literature points to the fact that the wettability of the underlying substrate is essential for determining the outcome of liquid impingement. The potential usefulness of wettability-patterned substrates, i.e., surfaces possessing spatially juxtaposed wettable and non-wettable domains, can also be inferred from those studies. From a scientific point of view, the interaction of liquid jets with wettability-patterned surfaces is a more complex problem than that of a single droplet. The complexity is further compounded when the substrate is permeable. The focus of the present dissertation is to study the interaction of high flow rate (~ 1 L/min) liquid jets with wettability-patterned permeable substrates. However, the inherent difficulty of the problem necessitates it to be divided into three modules. The first module is concerned with the interaction of liquid droplets with wettability-patterned permeable substrates, while the second module presents theoretical and experimental results of orthogonal liquid-jet impingement on wettability-patterned impermeable substrates. Finally, the third module demonstrates the applicability of wettability-patterned permeable substrates for manipulation of orthogonally impinging liquid jets.