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

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

Abstract

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.

Keywords

električni dvojni sloj;orientacijsko urejanje vodnih dipolov;Helmholtzeva prosta energija;evolucijski amodificiran Langevin Poisson-Boltzmannov model;electric double layer;orientational ordering of water dipoles;Helmholtz free energy;modified Langevin Poisson-Boltzmann model;

Data

Language:	English
Year of publishing:	2020
Typology:	1.01 - Original Scientific Article
Organization:	UL FE - Faculty of Electrical Engineering
UDC:	577
COBISS:	30268931
ISSN:	1099-4300
Views:	195
Downloads:	54
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary keywords:	električni dvojni sloj;orientacijsko urejanje vodnih dipolov;Helmholtzeva prosta energija;evolucijski modificiran Langevin Poisson-Boltzmannov model;
Type (COBISS):	Article
Pages:	str. 1-19
Volume:	ǂiss. ǂ9
Issue:	1054
Chronology:	Sep. 2020
DOI:	10.3390/e22091054
ID:	14229723