SFB 1313 Publication "Transport of thin water films: from thermally activated random walks to hydrodynamics"

New SFB 1313 publication, published in AIP - The Journal of Chemical Physics. The work has been developed within the SFB 1313 research project C01.

“Transport of thin water films: from thermally activated random walks to hydrodynamics”

Authors

• Simon Gravelle (University of Stuttgart, SFB 1313 research project C01)
• Christian Holm (University of Stuttgart, SFB 1313 research project C01)
• Alexander Schlaich (University of Stuttgart, SFB 1313 research project C01)

Abstract

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 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 porous material, we determine the humidity-dependent crossover between a vapor dominated and a thin film dominated transport regimes depending on the pore size.

Further information

All simulation scripts are available on the DaRUS, the data repository of the University of Stuttgart:

> Scripts: https://darus.uni-stuttgart.de/dataset.xhtml?persistentId=doi:10.18419/darus-2726
> Videos: https://darus.uni-stuttgart.de/dataset.xhtml?persistentId=doi:10.18419/darus-2697