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Water in an electric field does not dance alone: The relation between equilibrium structure, time dependent viscosity and molecular motions

Baer, Andreas; Miličević, Zoran; Smith, David M.; Smith, Ana-Sunčana (2019) Water in an electric field does not dance alone: The relation between equilibrium structure, time dependent viscosity and molecular motions. Journal of Molecular Liquids, 282 . pp. 303-315. ISSN 0167-7322

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Dynamic structuring of water is a key player in a large class of processes underlying biochemical and technological developments today, the latter often involving electric fields. However, the anisotropic coupling between the water structure and the field has not been understood on a molecular level so far. Here we perform extensive molecular dynamics simulations to explore the influence of an externally imposed electric field on liquid water under ambient conditions. Using self-developed analysis tools and rigorous statistical analysis, we unambiguously show that water hydration shells break into subcompartments, which were hitherto not observed due to radial averaging. The shape of subcompartments is sensitive to the field magnitude and affects excitations of the hydrogen bond network including the femtosecond stretching and the sub-picosecond restructuring of hydrogen bonds. Furthermore, by analysing the reorientational dynamics of water molecules, we ascertain the existence of cooperative excitations of small water clusters. Enabled by the interplay between hydrogen bonding, and the coupling of water dipoles to the field, these coordinated motions, occurring on the picosecond time scale, are associated with fluctuations between torque-free states of water dipoles. We show that unlike the coupling between translation and reorientation of water molecules, which takes place on even longer time scales, these coordinated motions are the key for understanding the emergent anisotropy of diffusion and viscosity of water. Particular effort is invested to provide an analysis that allows for future experimental validation.

Item Type: Article
Additional Information: ASS and AB acknowledge financial support by the Bavarian Ministry of Economic Affairs and Media, Energy and Technology for the joint projects in the framework of the Helmholtz Institute Erlangen Nurnberg for Renewable Energy (IEK-11) of Forschungszentrum Julich. ZM, DMS and ASS were funded by the Croatian structural funds project MIPOMAT and the FAU Erlangen Cluster of Excellence: Engineering of Advanced Materials.
Uncontrolled Keywords: electric field; structure; viscosity; molecular motions
Subjects: NATURAL SCIENCES > Physics
Divisions: Division of Physical Chemistry
Depositing User: Ana Sunčana Smith
Date Deposited: 12 Mar 2020 07:48
DOI: 10.1016/j.molliq.2019.02.055

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