Role of cationic organisation on water dynamics in saponite clays

27 July 2023, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Water dynamics impacts many phenomena from geosciences to biology, especiallly in confined environments. In the presence of charged interfaces, there are some ions the role of which with regards to the water dynamics is unclear. Here a synthetic saponite clay, which is oriented in a film, is used as confining medium in the bilayer state. It confines two water layers between negatively charged planes, the charge of which is compensated by sodium cations. Water dynamics is determined both parallel and perpendicular to the charged clay layers with Neutron Spin Echo (NSE). This technique gives access to long enough times and directly provides the intermediate scattering function that is calculated on the other hand by Molecular Dynamics (MD) simulations. These latter also enable the study of cations dynamics, not experimentally accessible on this time scale. The results point towards a huge role of these cations on the water dynamics, mainly through their local structure and localization between the charged confining planes.

Keywords

water dynamics
clays
confined water
neutron spin echo
molecular dynamics

Supplementary materials

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Supplementary information
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Figures not shown in the main text, for the interested reader. Methodology for the calculation of MSD of water molecules inside and outside cation hydration spheres.
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Neutron spin echo data
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The experimental data used in the article are shared in txt files (X and Y values with simple names).
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