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

热力学第二定律对所有热机的效率提出了一个基本的限制：卡诺定理告诉我们，效率系数应该小于热热源和冷热源的绝对温度之差，热热源的绝对温度归一化。另一方面，生物体中所有以效率著称的运动器官，都是在几乎等温的条件下，通过将化学能直接转化为机械运动来运作的，即通过卡诺循环以外的机制。提出的研究的动机是化学能直接转化为机械运动的基础和实际重要性，并将在复杂流体界面的背景下进行。目的是阐明这些界面的物理起源和量化自维持运动和拓扑变化的动力学。由于这些运动是由化学反应产生的表面活性物质（表面活性剂）驱动的界面（马兰戈尼）不稳定性引起的，我们将通过(1)确定这种不稳定性发生的条件，以及(2)揭示界面奇点在维持这种运动中的作用来实现这些目标。需要解决的实际问题包括：基于自我持续运动的各种设备的最有效运行的可行系统几何形状和物理条件是什么？

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.