Q-tensor model for electrokinetics in nematic liquid crystals

O. M. Tovkach, Christopher Conklin, M. Carme Calderer, Dmitry Golovaty, Oleg D. Lavrentovich, Jorge Viñals, Noel J. Walkington

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10 Scopus citations

Abstract

We use a variational principle to derive a mathematical model for a nematic electrolyte in which the liquid crystalline component is described in terms of a second-rank order parameter tensor. The model extends the previously developed director-based theory and accounts for the presence of disclinations and possible biaxiality. We verify the model by considering a simple but illustrative example of liquid crystal-enabled electro-osmotic flow around a stationary dielectric spherical particle placed at the center of a large cylindrical container filled with a nematic electrolyte. Assuming homeotropic anchoring of the nematic on the surface of the particle and uniform distribution of the director on the surface of the container, we consider two configurations with a disclination equatorial ring and with a hyperbolic hedgehog, respectively. The computed electro-osmotic flows show a strong dependence on the director configurations and on the anisotropies of dielectric permittivity and electric conductivity of the nematic, characteristic of liquid crystal-enabled electrokinetics. Further, the simulations demonstrate space charge separation around the dielectric sphere, even in the case of isotropic permittivity and conductivity. This is in agreement with the induced-charge electroosmotic effect that occurs in an isotropic electrolyte when an applied field acts on the ionic charge it induces near a polarizable surface.

Original languageEnglish (US)
Article number053302
JournalPhysical Review Fluids
Volume2
Issue number5
DOIs
StatePublished - May 2017

Bibliographical note

Funding Information:
Support from the following National Science Foundation Grants is acknowledged by the authors: No. DMS-1434969 (D.G. and O.M.T.), No. DMS-1435372 (C.K., M.C.C., and J.V.), No. DMS-1434185 (O.L.), No. DMS-1434734 (N.J.W.), and No. DMS-1418991 (N.J.W.). The authors thank Douglas Arnold for useful discussions regarding numerical simulations.

Publisher Copyright:
© 2017 American Physical Society.

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