Two shear driven flow regimes in microfluidic nematic devices: Tumbling and laminar

Abstract

The purpose of this study is to show how the tangential component of the shear stress (SS) σzx applied to the boundary of the microsized nematic channel containing a temperature gradient ∇T effects the character of director field n̂ evolution to its stationary orientation n̂st. Calculations based on extension of the classical Ericksen-Leslie theory, supplemented by thermomechanical correction of the stress tensor and Rayleigh dissipation function, with accounting the entropy balance equation, show that due to coupling among the SS σzx,∇T, and ∇n̂ in confined hybrid aligned nematic (HAN) channel the horizontal nematic flow v may be excited. Calculations also show that there is a difference in the evolution of n̂ to its stationary orientation n̂st, in the “laminar” case of confined nematic phase, composed of 4-cyano-4′-pentylbiphenyl(5CB) molecules, when -γ2/γ1>1, and in the “tumbling” case of confined nematic phase, composed of 4-cyano-4′-octylbiphenyl(8CB) molecules, when -γ2/γ1<1, respectively. It has been also shown the possible way how to set up a temperature difference ΔT=Tup-Tlw across the HAN microfluidic channel, initially equal to zero, under the action of σzx applied to the boundary of the HAN channel.