Theoretical Studies of Near-Critical Fluids in Dilute Porous Media

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Andrea Liu is supported by a Faculty Early Career Development Award from the Theoretical and Computational Chemistry Program to study equilibrium phase behavior and diffusive transport in near-critical fluids, such as vapor-liquid systems or binary liquid mixtures, confined in dilute porous media such as silica gels. In general, the behavior of a near-critical fluid in a porous medium is an extremely difficult theoretical problem, because the surface of the medium strongly prefers one phase of the fluid and because the structure of the medium is highly disordered. The approach used by Liu focuses on the strong interaction between the fluid and the surface; previous theoretical work has assumed that the interaction is weak and that disorder is the dominant factor. The keystone of the proposal is a model of the confining medium as a simple periodic network of cylindrical strands, which Liu has solved within the mean-field approximation. The proposed work builds on this basic model by using a coordinated combination of analytic and numerical techniques to investigate the effects of critical fluctuations and long-wavelength disorder in the gel structure, as well as the nonequilibrium behavior. This approach represents the best hope of isolating the effects of surface interactions and of disorder in the geometry of the medium in order to determine their relative importance for equilibrium and nonequilibrium behavior. The proposed education plan is centered around effective scientific communication. The objectives are to demystify science for non-majors and to convince them that chemistry is an important and interesting part of daily life, and to teach majors and graduate students how to communicate their work more effectively. Nearly critical fluids in dilute porous media, such as those studied by Liu, are models for more general multiphase fluids in more realistic porous media. Applications that are of industrial importance range from catalysis in porous beds, to storage of liquid wastes and liquid fuels in porous glasses, to the extraction of liquids such as oil from porous media like sandstone. An improved theoretical understanding of transport in porous media could have a significant impact in several of these strategic areas.