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Water Adsorption on Mica Surfaces with Hydrophilicity Tuned by Counterion Types (Na, K, and Cs) and Structural Fluorination

Author(s): Koishi, Ayumi; Lee, Sang Soo; Fenter, Paul; Fernandez-Martinez, Alejandro; Bourg, Ian C

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Abstract: The stability of adsorbed water films on mineral surfaces has far-reaching implications in the Earth, environmental, and materials sciences. Here, we use the basal plane of phlogopite mica, an atomically smooth surface of a natural mineral, to investigate water film structure and stability as a function of two features that modulate surface hydrophilicity: the type of adsorbed counterion (Na, K, Cs) and the substitution of structural OH groups by F atoms. We use molecular dynamics (MD) simulations combined with in situ high-resolution X-ray reflectivity to examine surface hydration over a range of water loadings, from the adsorption of isolated water molecules to the formation of clusters and films. We identify four regimes characterized by distinct adsorption energetics and different sensitivities to cation type and mineral fluorination: from 0 to ½ monolayer film thickness, the hydration of adsorbed ions; from ½ to 1 monolayer, the hydration of uncharged regions of the siloxane surface; from 1 to 1½ monolayer, the attachment of isolated water molecules on the surface of the first monolayer; and for > 1½ monolayer, the formation of an incipient electrical double layer at the mineral-water interface.
Publication Date: 20-Sep-2022
Citation: Koishi, Ayumi, Lee, Sang Soo, Fenter, Paul, Fernandez-Martinez, Alejandro, Bourg, Ian C. (2022). Water Adsorption on Mica Surfaces with Hydrophilicity Tuned by Counterion Types (Na, K, and Cs) and Structural Fluorination. The Journal of Physical Chemistry C, 126 (38), 16447 - 16460. doi:10.1021/acs.jpcc.2c04751
DOI: doi:10.1021/acs.jpcc.2c04751
ISSN: 1932-7447
EISSN: 1932-7455
Pages: 16447 - 16460
Language: en
Type of Material: Journal Article
Journal/Proceeding Title: The Journal of Physical Chemistry C
Version: Author's manuscript

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