Fundamentals and Applications of Liquid Drop Interactions with Complex Surfaces

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The proposed research is a unique program that seeks to understand the behavior of complex surfaces and their interactions with liquid drops. Specifically, it will tackle areas of drop motion on a surface, fabrication of novel opto-fluidic devices based on liquid bridges, and drop impact onto complex (e.g. woven textile) 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), protective textile and clothing, or biotechnology (e.g. accurate dispensing in PCR machines).A comprehensive study of incipient motion of sessile drop arrangements placed on a simple (smooth hydrophobic or hydrophilic), or a complex (patterned) surface exposed to a shearing airflow will be done. We will seek relations between drop properties, arrangement geometry and air velocity for incipient motion of drops on a surface. Through surface engineering strategies we seek to further assist the shedding of drops, by a shearing airflow, using patterned surfaces with hydrophobic and hydrophilic regions.Gaining fundamental knowledge about how to transfer liquids using a liquid bridge (e.g. used in dispensing and printing industries) is the key to advance such processes. We will study the complex case of bridges between non-parallel surfaces to understand the role of surface wettabilities, and dihedral angle between surfaces, in liquid transfer. In doing so we will consider liquid properties (surface tension, viscosity, etc.) and study both dynamic and quasi-static regimes. We have recently shown that by mechanically stimulating a liquid bridge, we can make a varifocal liquid lens; but to improve the response time of the lens, we will explore morphological changes of a liquid bridge under an electrical stress to develop novel optofluidic devices (e.g. a varifocal cylindrical lens). Simultaneous impact of multiple drops onto moving surfaces will be studied with the aim of understanding the impact morphology (e.g. splash limits, and resting drop shapes). Also, a systematic study of a single drop impact onto surfaces covered with a thin layer of an immiscible liquid will provide the fundamental information regarding the modes of drop-film interactions, e.g. film entrainment, bouncing, splashing, etc. A first comprehensive study of drop impact onto woven surfaces will allow determining the effectiveness of the claims made recently about protective nature of liquid infused or superhydrophobic textiles.This proposal, at its core, is designed to provide training for 20 students at different levels. They will gain skills needed for Canada's knowledge based economy by working on advanced imaging systems, surface fabrication and characterization, as well as analytical and modeling techniques. Communication skills will be honed through disseminating their findings.