Chemical-to-mechanical energy conversion at fluid interfaces: study of the fundamental properties and applications

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The second law of thermodynamics puts a fundamental limit on the efficiency of all heat engines: the Carnot theorem tells us that the efficiency coefficient should be less than the difference between the absolute temperatures of the hot and cold heat reservoirs normalized by that of the hot reservoir. On the other hand, all motor organs in living organisms, known for their efficiency, operate through the conversion of chemical energy directly into mechanical motion under almost isothermal conditions, i.e. through mechanisms other than the Carnot cycle. The proposed research is motivated by the fundamental and practical importance of the direct conversion of chemical energy into mechanical motion and will be performed in the context of complex fluid interfaces. The goals are to elucidate the physical origin and quantify the dynamics of self-sustained motions and topological changes of such interfaces. Since the motions arise due to interfacial (Marangoni) instabilities, driven by surface-active substances (surfactants) produced by chemical reactions, we will achieve these goals by (1) identifying the conditions when such instabilities occur, and (2) uncovering the role of interfacial singularities in sustaining such motions. Among the practical questions to be addressed are: what are the feasible system geometries and physical conditions for the most efficient operation of various devices based on self-sustained motions?This research effort will require novel theoretical tools and experimental capabilities. On the experimental side, in the laboratory we will study self-sustained motions as well as design and test isothermal motors based on them. While a limited number of such chemical reactions leading to interfacial motions have been identified in the literature, whether or not these are the most energy-efficient choices has yet to be determined. On the theoretical side, as a part of the longer-term objective, this work will lead to elaboration of new geometrically inspired (coordinate-free) theoretical methods based on the synergy of dynamical systems, differential geometry, singularity theories, and nonequilibrium thermodynamics. Such a theoretical framework for studying self-induced interfacial motion phenomena is a necessary step towards developing reliable computational methods for these multiscale systems, and designing real applications with desired functions. The proposed program will also help us to understand the interplay between singularity and instability phenomena and thus to make progress on Arnold's problem of unifying Cartan's and singularity theories.This work draws on the PI's unique combined expertise in both theoretical and experimental interfacial fluid dynamics as well as geometric methods of analysis. The experiments will be performed in the PI’s laboratory, the infrastructure for which is provided by both the Mechanical Engineering and Physics Departments.