UNS: Exploiting novel surface rheology to probe and tailor 2D suspension dynamics

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The goal of the proposed research is to discover and understand phenomena that occur in two-dimensional suspensions of particles. These are particles that are suspended in solutions that are so spread-out that they form what are known as monolayer suspensions. This is a very fundamental problem with industrial and biological implications, since such suspensions are very common in both industry and nature, including emulsions and foams, cells, organelles and biological fluids. The proposal is focused on the understanding of the rheological behavior of particulate dispersions embedded in insoluble monolayers of surfactants. Carefully conceived theoretical and experimental studies of model two-dimensional particulate dispersions are proposed. It is very important to note that the choice of a 2D system was made so that study of the lubrication phenomena in flows between approaching particles can reveal new modes of behavior in interfacial suspensions that have no analog in conventional three dimensional suspensions. In other words, this is a case where the investigation of a 2D system offers as rich a field of exploration and relevance to the real world as the investigation of 3D systems. The proposed research will involve theoretical analysis of a series of paradigmatic problems (e.g. lubrication flows and colloidal pair dynamics) involving monolayers whose surface rheology thickens, thins, or exhibits phase transitions as a function of surface pressure. It will also involve complementary experiments using photolithographically-designed particles and structures dispersed within surfactant monolayer. Exploratory experimental studies of concentrated 2D suspensions, including detailed particle dynamics, effective rheology, and discontinuous shear thickening will be conducted. Outreach and dissemination of research is planned, involving URM students in research. In addition, there are activities planned to reach out to 4th-6th grade students and attract them to mechanical, computer, and chemical engineering.