Fundamentals and Applications of Liquid Drop Interactions with Engineered Surfaces

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The proposed research is a unique program that seeks to understand the behavior of advanced materials and their interactions with liquid drops. Specifically, it will tackle areas of drop motion on a surface, fabrication of textured surfaces and understanding their wetting, and drop impact onto complex surfaces. This research can produce the necessary knowledge to enable advanced technologies of strategic importance today, such as, energy systems (e.g. efficient condensers, and water management for fuel cells), or biotechnology (e.g. printing of living cells, and lab-on-a-chip). A comprehensive study of incipient motion of a sessile drop placed on a simple (smooth hydrophobic or hydrophilic), or a complex (textured) surface exposed to a shearing airflow will be done. We will seek relations between drop properties and air velocity for incipient motion. As airflow will cause drop oscillations, scaling laws for understanding the oscillation frequency with respect to drop size and properties such as contact angle, and viscosity will be developed. This enables understanding of how oscillations can aid or hinder shedding. Free energy analysis will be used to study the effect of topography, specifically sharp edges, on apparent contact angle as well as liquid penetration into troughs of a textured surface. We will also fabricate novel multifunctional textured surfaces, specifically, a textured surface that has dual functionality of being superhydrophobic and electrically conductive, so it can be resistively heated. Drop impact onto bulk soft surfaces will be studied with the aim of understanding surface deformation, and impact morphology (e.g. splash limits, resting drop shapes, and oscillation times), in comparison to impact on regular "hard" surfaces of similar wettabilities and roughness. Also, a systematic study of a single drop and a single particle collision in midair will be done to provide the fundamental information regarding the modes of drop-particle interactions, e.g. coalescence, bouncing, or shattering, etc. This proposal, at its core, is designed to provide advanced training for 17 students at different levels.