Solid/Liquid Interactions on Wettability-Modified Surfaces

This thesis explores the intricate domain of solid-fluid interaction on wettability-modified surfaces, addressing novel and underexplored aspects in the field. It investigates the fundamental studies that contribute to a deeper understanding with a specific focus on parametric investigations that have been lacking in existing literature. The first part of the thesis unfolds with an examination of single droplet impact on non-uniform wettability surfaces. The investigation involves experimental characterizations of axisymmetric droplet impact on a circular area with a specific wettability, surrounded by a region exhibiting different wettability properties. Three distinct regimes of droplet spreading: I) Interior spreading, II) Contact-line entrapment, and III) Exterior spreading are identified depending on the droplet momentum. A theoretical analysis, based on energetic principles, is also presented and compared to experimental observations to enhance further understanding. The second part of the thesis concentrates on understanding the impact of liquid-jet impingement on superhydrophobic metal meshes, probing into the influence of flow parameters, mesh geometry, and liquid properties. The investigation delves further into the different regimes of jet impact—prebreakthrough, breakthrough, and post-breakthrough, offering comprehensive insights into the dynamics of these phases. In the final segment, the focus shifts towards the fabrication of superoleophobic surfaces capable of repelling very low surface tension liquids. The study successfully designs and fabricates surfaces that can repel very low surface tension liquids like octane (21.14 mN m−1) and arrest the spreading of even lower surface tension liquids like heptane (19.74 mN m−1) using a facile and straightforward technique. By unraveling the complexities of these solid-fluid interaction studies, this thesis provides a robust foundation for the design of engineering devices for diverse technological domains, particularly in microfluidic applications like lab-on-a-chip technology. The potential applications of this research span high-rate fluidic transport, enhanced condensation heat transfer, water capture, area-selective cooling, and hydrodynamic drag reduction.