Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate

Abstract

Lyotropic chromonic liquid crystals (LCLCs) represent aqueous dispersions of organic disk-like molecules that form cylindrical aggregates. Despite the growing interest in these materials, their flow behavior is poorly understood. Here,...

In Situ Visualization of the Structural Evolution and Alignment of Lyotropic Liquid Crystals in Confined Flow

“…However, the perpendicular orientation found in the central area, where the velocity is maximum as well as the elongation component of the flow, contradicts the expected orientation due to flow. Such perpendicular orientation has been previously observed for nematic structures in other flow‐based systems including in simple shear flow, [ 45,46 ] flow assisted by interfacial forces during film formation, [ 47 ] and simple shear flow (coating) followed by drying. [ 48 ] In the absence of other effects, the orthogonal orientation was explained in terms of the interplay between elastic‐dominated and viscous‐dominated flow regimes.…”

“…[ 50 ] In simple shear flow, at high shear rates where viscous forces dominant (large Er ), the director was aligned in the flow direction, whereas at low shear rates (small Er ) where elastic forces are dominant, lyotropic chromonic liquid crystals were found oriented perpendicularly to the flow direction. [ 45,46 ] For pressure‐driven channel flows, such as the ones investigated in this work, where one characteristic velocity would determine the Er of the channel flow, [ 51 ] it is important to note that locally in the channel cross section there is a velocity gradient and as a consequence the shear rate varies locally. [ 52 ] Thus, near the channel walls, where the velocity gradients are high, viscous forces would be expected to dominate resulting in a director orientation in the flow direction.…”

Interplay of Active Stress and Driven Flow in Self-Assembled, Tumbling Active Nematics

“…Consequently, the directors escape from the yz plane, forming the so-called log-rolling state, trading splay-bend energy with twist energy. Log-rolling state has been studied in nematic DSCG solution experiments under different external flow conditions, where the directors are found pointing towards the vorticity direction at certain shear rates [48,49]. The stability of this state requires a low twist modulus [53], as is considered in our simulation.…”

“…For a flow-tumbling nematic with α 3 > 0 and α 2 < 0, however, directors cannot settle into a stationary orientation and thereby tumble persistently. Recent experiments of nematic DSCG solutions have uncovered its tumbling character, manifested by the emergence of a log-rolling state at intermediate shear rates [48,49]. In this state, directors tend to rotate out of the shear plane and roll with respect to the vorticity direction, reminiscent of logs rolling on the ground [48].…”

“…These existing simulation studies of tumbling active nematics, however, use one-elastic-constant approximation. The log-rolling mode is intrinsically a three-dimensional (3D) phenomenon and requires low twist constant [48,53]. To the best of our knowledge, 3D tumbling dynamics in active nematics have not been discussed.…”