Liquid Crystal Microfluidics for Tunable Flow Shaping

Abstract

We explore the flow of a nematic liquid crystal in microfluidic channels with a rectangular cross section through experiments and numerical modeling. The flow profile and the liquid crystal orientational profile show three distinct regimes of weak, medium, and strong flow as the driving pressure is varied. These are identified by comparing polarizing optical microscopy experiments and numerical solutions of the nematofluidic equations of motion. The relative stability of the regimes is related to the de Gennes characteristic shear-flow lengths e(1) and e(2), together with the channel's aspect ratio w/d. Finally, we show that the liquid crystalline microfluidic flow can be fully steered from left to right of a simple microchannel by applying transverse temperature gradients.

Transport of particles in liquid crystals

“…Simplicity of the phenomenon that does not require pumps nor even electrodes to produce dramatic optical and mechanical changes suggests that it might find applications in sensors, photonics, lab-on-a-chip, microand optofluidics. All these fields started to explore benefits offered by LC as a functional microfluidic and optofluidic medium [168][169][170][171][172][173] . …”

The effect of anchoring on the nematic flow in channels

“…Zhou and Forest 20 performed calculations for two-dimensional flow in the low-flow-rate, strong-anchoring limit for the cases of homeotropic, planar and tilted anchoring. Sengupta et al 21,22 performed experiments and lattice Boltzmann simulations of flow in rectangular channels over a wider range of flow rates. Feng and Leal 23 and Quintans Carou et al 24 investigated, by analytical and numerical techniques, nematic flow between plates of narrowing or widening separation, while Manneville and Dubois-Violette 25 and Tarasov et al 26 investigated the onset of instabilities in channel flow.…”

Flow and Nematic Director Profiles in a Microfluidic Channel: The Interplay of Nematic Material Constants and Backflow

“…We work within the standard and powerful Beris-Edwards theoretical framework for nematodynamics [24]. There are three governing equations: the incompressibility constraint, an evolution equation for the flow field, which is essentially the Navier-Stokes equation with an additional stress (σ) due to the nematic ordering and an evolution equation for q, which has an additional stress induced by the fluid vorticity.…”

“…We fix the parameters L * = 10 −3 and L 1 = 10 −6 , which are physically relevant values from the typical values of material constants reported in the literature and investigate the effects of the parameters,p x and L 2 on the solution profiles for Equations (9)-(11) [9,24]. The results are presented in Figures 2 and 3 where we plot the no-flow profiles fors and θ for reference and then compare these profiles to the distorted profiles with a non-zero pressure gradient p x .…”

“…In parallel, there are several papers that focus on the role of backflow in the hydrodynamics of defects, in the Beris-Edwards framework, see for example [12,21,22]. In recent years, there are rigorous existence and regularity results for the Beris-Edwards framework too [11,14,23] and numerical simulations for microfluidic set-ups in [24,25]. The various dynamical theories of nematic liquid crystals and the key results are surveyed in [26] and in [27]; the authors rigorously derive the Ericksen-Leslie equations from the Beris-Edwards model.…”