Title: Fluctuation-enhanced electric conductivity in electrolyte solutions

Abstract

In this work, we analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson–Nernst–Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation–anion diffusion coefficient. Specifically, we predict a nonzero cation–anion Maxwell– Stefan coefficient proportional to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye–Huckel–Onsager theory, while elucidating the physical origins ofmore » these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Lastly, we show that strong applied electric fields result in anisotropically enhanced “giant” velocity fluctuations and reduced fluctuations of salt concentration.« less

Authors:

Péraud, Jean-Philippe ^[1]; Nonaka, Andrew J. ^[1]; Bell, John B. ^[1]; Donev, Aleksandar ^[2]; Garcia, Alejandro L. ^[3]

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+ Show Author Affiliations

1. Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94703,
2. Department of Mathematics, Courant Institute of Mathematical Sciences, New York University, New York, NY 10012,
3. Department of Physics and Astronomy, San Jose State University, San Jose, CA 95192

Publication Date:

Tue Sep 26 00:00:00 EDT 2017

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR)

OSTI Identifier:

1396062

Alternate Identifier(s):

OSTI ID: 1426738

Grant/Contract Number:  

AC02-05CH11231; SC0008271

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 114 Journal Issue: 41; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

97 MATHEMATICS AND COMPUTING; fluctuating hydrodynamics; electrohydrodynamics; Navier–Stokes equations; multicomponent diffusion; Nernst–Plank equations