When an ion transports from water to oil through water-oil interface, it accompanies hydrated water molecules and transiently forms a chain of water, called “water finger.” We thoroughly investigated the role of the water finger in chloride ion transport through water-dichloromethane interface by using molecular dynamics technique. We developed a proper coordinate w to describe the water finger structure and calculated the free energy landscape and the friction for the ion transport as a function of ion position z and the water finger coordinate w. It is clearly shown that the formation and break of water finger accompanies an activation barrier for the ion transport, which has been overlooked in the conventional free energy curve along the ion position z. The present analysis of the friction does not support the hypothesis of augmented local friction (reduced local diffusion coefficient) at the interface. These results mean that the experimentally observed rate constants of interfacial ion transfer are reduced from the diffusion-limited one because of the activation barrier associated to the water finger, not the anomalous local diffusion. We also found that the nascent ion just after the break of water finger has excessive hydration water than that in the oil phase.
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7 July 2016
Research Article|
July 01 2016
Computational study of effect of water finger on ion transport through water-oil interface
Nobuaki Kikkawa;
Nobuaki Kikkawa
1Department of Chemistry, Graduate School of Science,
Tohoku University
, Sendai 980-8578, Japan
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Lingjian Wang;
Lingjian Wang
1Department of Chemistry, Graduate School of Science,
Tohoku University
, Sendai 980-8578, Japan
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Akihiro Morita
Akihiro Morita
a)
1Department of Chemistry, Graduate School of Science,
Tohoku University
, Sendai 980-8578, Japan
2Elements Strategy Initiative for Catalysts and Batteries (ESICB),
Kyoto University
, Kyoto 615-8520, Japan
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a)
E-mail: morita@tohoku.ac.jp
J. Chem. Phys. 145, 014702 (2016)
Article history
Received:
April 14 2016
Accepted:
June 13 2016
Citation
Nobuaki Kikkawa, Lingjian Wang, Akihiro Morita; Computational study of effect of water finger on ion transport through water-oil interface. J. Chem. Phys. 7 July 2016; 145 (1): 014702. https://doi.org/10.1063/1.4954774
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