Title: Theory of ice premelting in porous media

Author (Talk): Hendrik Hansen-Goos, Yale University

Abstract:

Hendrik Hansen-Goos (1) and J. S. Wettlaufer (1,2,3) (1) Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA (2) Department of Physics, Yale University, New Haven, CT 06520, USA (3) Program in Applied Mathematics, Yale University, New Haven, CT 06520, USA The availability of liquid water is crucial for the survivial of organisms at low temperatures, e.g., in terrestrial habitats like the polar regions or extraterrestrial settings such as Mars. The phenomena of premelting is responsible for the persistence of liquid water at temperatures well below its bulk freezing point. In the bulk system, a freezing point depression occurs due to the colligative effect of dissolved impurities such as salts and due to grain boundary melting in ice. Finally, in contact with a foreign matrix, such as a colloid or a soil grain, interfacial premelting in planar regions and interfacial curvature induced premelting in regions where the shape of the matrix imposes strong curvature on the ice-liquid interface are both prevalent. We present a theoretical decription of the premelting of water ice contained in a porous matrix, made of a material with a melting temperature substantially larger than ice itself, to predict the amount of liquid water in the matrix at temperatures below its bulk freezing point. Our theory combines interfacial and curvature-induced premelting at the surface of the porous matrix and grain-boundary melting in the ice in the presence of dissolved impurities. Due to the small segregation coefficient in ice, impurities enrich the premelted liquid thereby enhancing premelting in partially frozen soils. Our principal result is an equation for the fraction of liquid in a porous medium as a function of the undercooling, the impurity concentration, the degree of polycrystallinity of the interstitial ice, the matrix material, and the average matrix particle size. The result is analyzed in detail and applied to a range of experimentally relevant settings.

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