Long-range dipolar order and dispersion forces in polar liquids

Besford, Q, Christofferson, A, Liu, M and Yarovsky, I 2017, 'Long-range dipolar order and dispersion forces in polar liquids', Journal of Chemical Physics, vol. 147, no. 19, pp. 1-8.

Document type: Journal Article
Collection: Journal Articles

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Title Long-range dipolar order and dispersion forces in polar liquids
Author(s) Besford, Q
Christofferson, A
Liu, M
Yarovsky, I
Year 2017
Journal name Journal of Chemical Physics
Volume number 147
Issue number 19
Start page 1
End page 8
Total pages 8
Publisher A I P
Abstract Complex solvation phenomena, such as specific ion effects, occur in polar liquids. Interpretation of these effects in terms of structure and dispersion forces will lead to a greater understanding of solvation. Herein, using molecular dynamics, we probe the structure of polar liquids through specific dipolar pair correlation functions that contribute to the potential of mean force that is "felt" between thermally rotating dipole moments. It is shown that unique dipolar order exists at separations at least up to 20 Å for all liquids studied. When the structural order is compared with a dipolar dispersion force that arises from local co-operative enhancement of dipole moments, a strong agreement is found. Lifshitz theory of dispersion forces was compared with the structural order, where the theory is validated for all liquids that do not have significant local dipole correlations. For liquids that do have significant local dipole correlations, specifically liquid water, Lifshitz theory underestimates the dispersion force by a factor of 5-10, demonstrating that the force that leads to the increased structure in liquid water is missed by Lifshitz theory of van der Waals forces. We apply similar correlation functions to an ionic aqueous system, where long-range order between water's dipole moment and a single chloride ion is found to exist at 20 Å of separation, revealing a long-range perturbation of water's structure by an ion. Furthermore, we found that waters within the 1st, 2nd, and 3rd solvation shells of a chloride ion exhibit significantly enhanced dipolar interactions, particularly with waters at larger distances of separation. Our results provide a link between structures, dispersion forces, and specific ion effects, which may lead to a more robust understanding of solvation.
Subject Theoretical and Computational Chemistry not elsewhere classified
Keyword(s) Molecular-Dynamics Simulations
Methanol-Water Mixtures
Lifshitz Theory
Hofmeister Series
DOI - identifier 10.1063/1.5005581
Copyright notice © 2017 Author(s)
ISSN 0021-9606
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