Nematic line defects in microfluidic channels: wedge, twist and zigzag disclinations

Abstract

We report an experimental study of structural transformations of disclination lines in nematic liquid crystals in microfluidic channels. The anchoring conditions of the channel walls enforce the generation of a disclination line of the wedge type in the absence of flow. The wedge disclination is transformed to a twist disclination by the flow of the nematic liquid crystal in the channel. The application of an electric field perpendicular to the channel axis induces a second transformation to a zigzag shape. The threshold field strength for the second transformation increases with increasing flow velocity. The experimental results are compared to predictions based on model director fields of the different disclination structures.

Microfluidic control over topological states in channel-confined nematic flows

“…To the best of our knowledge, orientational phase transitions with chiral instabilities in homogeneous nematic flows have not been discussed in the framework of experiments, theoretical modelling or numerical simulations, though localised twist deformations in an electric field have been recently demonstrated in different setups and contexts—in 2D Poiseuille flows under effect of an electric field, measured by Pieranski et al 32 , or by backflows caused by pulsed electric fields in 2D pattern formation by Migara et al 59 . The recent publication by Agha and Bahr 60 reports wedge to twist to zigzag structural transformation of nematic disclination lines under the influence of anchoring, flow and electric field.…”

Electrically controlled topological micro cargo transportation

“…2,16 We have used hybrid alignment of a nematic layer to create two stable coexisting equilibrium n-director tilt orientations which are separated by an elastic domain wall that contains a line defect. Previous work on the formation 17 of a topological defect line and its structural transformation [18][19][20] under hybrid alignment conditions has been reported for confinement in thin microchannels.…”

A Multi-Faceted Study of Nematic Order Reconstruction in Microfluidic Channels

“…There are two obvious solutions of (3.8) i.e. Q 11 ≡ 0 (i.e., ω = ± 1 4 ), or Q 12 ≡ 0 (i.e., ω = 0, ± 1 2 ), everywhere on Ω.…”

“…OR solutions are nematic profiles with distinct director polydomains, separated by singular lines or singular surfaces, referred to as domain walls. OR solutions are relevant for modelling chevron or zigzag patterns observed in pressuredriven flows [1,11], as well as in active nematics where aligned fibers confined in narrow channels can be controlled to display a laminar flow [20]. OR solutions have been studied in purely nematic systems, for example [23], [9] and [8].…”