Weak Anchoring and Surface Elasticity Effects in Electroosmotic Flow of Nematic Liquid Crystals Through Narrow Confinements

TL;DR

This study investigates how surface anchoring and elasticity influence electroosmotic flow of nematic liquid crystals in microchannels, revealing complex director deformations and flow behaviors under weak anchoring conditions and electric fields.

Contribution

It introduces a coupled flow model incorporating second-order elasticity and weak anchoring effects for nematic liquid crystals in microfluidic electroosmosis.

Findings

Surface charge and elasticity significantly affect flow characteristics.

Optical stripe patterns emerge at higher electric fields.

Director deformations are accurately captured with second-order elasticity.

Abstract

Advent of nematic liquid crystals flows have attracted renewed attention in view of microfluidic transport phenomena. Among various transport processes, electroosmosis stands as one of the efficient flow actuation method through narrow confinement. In the present study, we explore the electrically actuated flow of a nematic fluid with ionic inclusions taking into account the influences from surface induced elastic and electrical double layer phenomena. Influence of surface effects on the flow characteristics is known to get augmented in micro-confined environment and must be properly addressed. Towards this, we devise the coupled flow governing equations from fundamental free energy analysis considering the contributions from first and second-order elastic, dielectric, flexoelectric, ionic and entropic energies. We have further considered weak anchoring surface conditions with second order elasticity which helps us to more accurately capture the director deformations along the boundaries. The present study focuses on the influence of surface charge and elasticity effects in the resulting linear electroosmosis through a slit-type microchannel whose surface are considered to be chemically treated in order to display a homeotropic-type weak anchoring state. An optical periodic stripe configuration of the nematic director has been observed especially for higher electric fields wherein the Ericksen number for the dynamic study is restricted to the order of unity.