Experimental and theoretical insights into impact phenomena of small scale liquid interfacial systems

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PhD; 2023; Mechanical engineering

This work explores impact phenomena experimentally and theoretically for various interfacial systems ranging from medical diagnostics to drop impacts on solids and immiscible liquids. We study a hitherto unexplored impact phenomenon during an ophthalmology procedure called Non-Contact Tonometry. Using high fidelity experiments and theoretical modeling, we show that noninvasive ocular diagnostics demonstrate a propensity for droplet generation and present a potential pathway for pathogen transmission. The air puff-induced corneal deformation and subsequent capillary waves lead to flow instabilities (Rayleigh–Taylor, Rayleigh–Plateau) that lead to tear film ejection, expansion, stretching, and subsequent droplet formation. Effective cooling is one of the significant application areas of impact systems. In the context of cooling problems, we provide new insights using ab initio scaling and boundary layer analysis of the integral and differential forms of the conservation equations. We have probed the limiting scaling regimes by incorporating the evap- orative effects at the liquid-vapor interface. The dependence of liquid film thickness and Nusselt number on various non-dimensional numbers has been explored. We then investigate the class of drop impact problems where we study impacts on solids, bio-inspired substrates, and immiscible liquid pools at low to moderate impact en- ergies. We explore impacts on glass, PDMS, and soft lithographically fabricated replicas of the lotus leaf and rose petals. Surprisingly, the rose petal and lotus leaf replicas manifest similar impact dynamics. The observation is extremely intriguing and counter-intuitive, as rose petals and their replicas are sticky in contrast to lotus leaves.