Under ambient atmospheric conditions, a thin film of water wets many solid surfaces, including insulators, ice, and salt. The film thickness as well as its transport behavior sensitively depend on the surrounding humidity. Understanding this intricate interplay is of the highest relevance for water transport through porous media, particularly in the context of soil salinization induced by evaporation. Here, we use molecular simulations to evaluate the transport properties of thin water films on prototypical salt and soil interfaces, namely NaCl and silica solid surfaces. Our results show two distinct regimes for water transport: at low water coverage, the film permeance scales linearly with the adsorbed amount, in agreement with the activated random walk model. For thicker water films, the permeance scales as the adsorbed amount to the power of 3, in line with the Stokes equation. By comparing results obtained for silica and NaCl surfaces, we find that, at low water coverage, water permeance at the silica surface is considerably lower than at the NaCl surface, which we attribute to difference in hydrogen bonding. We also investigate the effect of atomic surface defects on the transport properties. Finally, in the context of water transport through the porous material, we determine the humidity-dependent crossover between a vapor-dominated and a thin film-dominated transport regimes depending on the pore size.
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14 September 2022
Research Article|
September 13 2022
Transport of thin water films: From thermally activated random walks to hydrodynamics
Special Collection:
Fluids Meet Solids
Simon Gravelle
;
Simon Gravelle
(Conceptualization, Formal analysis, Investigation, Methodology, Writing – original draft)
1
Institute for Computational Physics, University of Stuttgart
, D-70569 Stuttgart, Germany
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Christian Holm
;
Christian Holm
(Funding acquisition, Methodology, Supervision, Writing – review & editing)
1
Institute for Computational Physics, University of Stuttgart
, D-70569 Stuttgart, Germany
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Alexander Schlaich
Alexander Schlaich
a)
(Conceptualization, Funding acquisition, Methodology, Supervision, Writing – review & editing)
1
Institute for Computational Physics, University of Stuttgart
, D-70569 Stuttgart, Germany
2
Stuttgart Center for Simulation Science (SC SimTech), University of Stuttgart
, 70569 Stuttgart, Germany
a) Author to whom correspondence should be addressed: schlaich@icp.uni-stuttgart.de
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a) Author to whom correspondence should be addressed: schlaich@icp.uni-stuttgart.de
Note: This paper is part of the JCP Special Topic on Fluids Meets Solids.
J. Chem. Phys. 157, 104702 (2022)
Article history
Received:
May 18 2022
Accepted:
August 07 2022
Citation
Simon Gravelle, Christian Holm, Alexander Schlaich; Transport of thin water films: From thermally activated random walks to hydrodynamics. J. Chem. Phys. 14 September 2022; 157 (10): 104702. https://doi.org/10.1063/5.0099646
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