Electric double layer and orientational ordering of water dipoles in narrow channels within a modified Langevin Poisson-Boltzmann model

Drab, Mitja (author), Gongadze, Ekaterina (author), Kralj-Iglič, Veronika (author), Iglič, Aleš (author)

The electric double layer (EDL) is an important phenomenon that arises in systems where a charged surface comes into contact with an electrolyte solution. In this work we describe the generalization of classic Poisson-Boltzmann (PB) theory for point-like ions by taking into account orientational ordering of water molecules. The modified Langevin Poisson-Boltzmann (LPB) model of EDL is derived by minimizing the corresponding Helmholtz free energy functional, which includes also orientational entropy contribution of water dipoles. The formation of EDL is important in many artificial and biological systems bound by a cylindrical geometry. We therefore numerically solve the modified LPB equation in cylindrical coordinates, determining the spatial dependencies of electric potential, relative permittivity and average orientations of water dipoles within charged tubes of different radii. Results show that for tubes of a large radius, macroscopic (net) volume charge density of coions and counterions is zero at the geometrical axis. This is attributed to effective electrolyte charge screening in the vicinity of the inner charged surface of the tube. For tubes of small radii, the screening region extends into the whole inner space of the tube, leading to non-zero net volume charge density and non-zero orientational ordering of water dipoles near the axis.

• Language: English
• Keywords: electric double layer, orientational ordering of water dipoles, Helmholtz free energy, modified Langevin Poisson-Boltzmann model
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FE - Faculty of Electrical Engineering; ZF - Faculty of Health Sciences
• Publication status: Published
• Publication version: Version of Record
• Year: 2020
• Number of pages: 19 str.
• Numbering: Vol. 22, iss. 9, art. 1054
• PID: 20.500.12556/RUL-134268
• UDC: 577
• ISSN on article: 1099-4300
• DOI: 10.3390/e22091054
• COBISS.SI-ID: 30268931
• Publication date in RUL: 04.01.2022

Record is a part of a journal

• Title: Entropy
• Shortened title: Entropy
• Publisher: MDPI
• ISSN: 1099-4300
• COBISS.SI-ID: 515806233

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.
• Licensing start date: 21.09.2020

Secondary language

• Language: Slovenian
• Keywords: električni dvojni sloj, orientacijsko urejanje vodnih dipolov, Helmholtzeva prosta energija, evolucijski modificiran Langevin Poisson-Boltzmannov model