Abstract
Charge profiles in liquid electrolytes are of crucial importance for applications such as supercapacitors, fuel cells, batteries, or the self-assembly of particles in colloidal or biological settings. However, creating localized (screened) charge profiles in the bulk of such electrolytes generally requires the presence of surfaces—for example, provided by colloidal particles or outer surfaces of the material—which poses a fundamental constraint on the material design. Here, we show that topological defects in nematic electrolytes can perform as regions for local charge separation, forming charged defect cores and, in some geometries, even electric multilayers, as opposed to the electric double layers found in isotropic electrolytes. Using a Landau-de Gennes-Poisson-Boltzmann theoretical framework, we show that ions highly effectively couple with the topological defect cores via ion solvability and with the local director-field distortions of the defects via flexoelectricity. The defect charging is shown for different defect types—lines, points, and walls—using geometries of ionically screened flat isotropic-nematic interfaces, radial hedgehog point defects, and half-integer wedge disclinations in the bulk and as stabilized by (charged) colloidal particles. More generally, our findings are relevant for possible applications where topological defects act as diffuse ionic capacitors or as ionic charge carriers.
- Received 29 September 2020
- Revised 27 November 2020
- Accepted 15 January 2021
DOI:https://doi.org/10.1103/PhysRevX.11.011054
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Control over electric charge in liquid electrolytes is crucial in many applications, such as supercapacitors, fuel cells, batteries, and self-assembly of particles in colloidal or biological settings. However, localizing the charge in the bulk of such applications generally requires the presence of surfaces, which poses a fundamental constraint on materials design. Contrary to that requirement, we show that special regions known as topological defects in nematic electrolytes can stabilize bulk charge separation without surfaces by coupling the internal order of the material to the charge organization.
Nematic electrolytes are fluids with an internal orientational order of its building blocks. If frustrated by geometry or external fields, these fluids can exhibit regions of broken order, called topological defects. In this work, we show that these defects can cause local charge separation by attracting electric charge of one sign to their cores and stabilizing the electric charge of the opposite sign in surrounding layers. The spatial profiles of the charge are determined by the distinct structure (topology) of the defects. We show that ion partitioning and flexoelectricity—a spontaneous electric polarization induced by strain—are the key mechanisms for realizing such electric multilayers.
More generally, our findings are relevant for possible applications where topological defects could act as diffuse ionic capacitors or as ionic charge carriers. Furthermore, this work elucidates the basic physical principles behind the formation of inhomogeneous ion distributions in nematic fluids.
