Charge-, salt- and flexoelectricity-driven anchoring effects in nematics

ABSTRACT

We investigate the effects of electric double layers and flexoelectricity on the surface anchoring in general nematic fluids. Within a simplified model, we demonstrate for a nematic electrolyte how the surface anchoring strength can be affected by the surface charge, bulk ion concentration and/or flexoelectricity, effectively changing not only the magnitude of the anchoring but also the anchoring type, such as from planar to tilted. In particular, we envisage possible tuning of the anchoring strength by the salt concentration in the regime where sufficiently strong electrostatic anchoring, as controlled by the (screened) surface charge, can compete with the non-electrostatic anchoring. This effect is driven by the competing energetic-torque couplings between nematic director and the emergent electrostatic potential, due to surface charge, ions and flexoelectricity. Our findings propose a way of influencing surface anchoring by using electrostatic effects, which could be used in various aspects, including in the self-assembly of colloidal particles in nematic fluids, optical and display patterns, and sensing.

Graphical Abstract

KEYWORDS:

• Surface anchoring
• charge regulation
• flexoelectricity
• dielectric anisotropy
• electrostatic screening

Acknowledgments

The authors acknowledge I. Smalyukh and S. Čopar for fruitful discussions. Finally, the authors would like to thank the Isaac Newton Institute for Mathematical Sciences for support and hospitality during the programme [The Mathematical Design of New Materials] when part of this work on this paper was undertaken.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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Funding

This work was supported by the Engineering and Physical Sciences Research Council [EP/R014604/1]; H2020 Marie Skłodowska-Curie Actions Grant agreement no. [795377]; Javna Agencija za Raziskovalno Dejavnost RS [J1-1697,L1-8135,P1-0099,J1-9149].