Abstract
Nematic and columnar phases of lyotropic chromonic liquid crystals (LCLCs) have been long studied for their fundamental and applied prospects in material science and medical diagnostics. LCLC phases represent different self-assembled states of disc-shaped molecules, held together by noncovalent interactions that lead to highly sensitive concentration and temperature dependent properties. Yet, microscale insights into confined LCLCs, specifically in the context of confinement geometry and surface properties, are lacking. Here, we report the emergence of time dependent textures in static disodium cromoglycate (DSCG) solutions, confined in PDMS-based microfluidic devices. We use a combination of soft lithography, surface characterization, and polarized optical imaging to generate and analyze the confinement-induced LCLC textures and demonstrate that over time, herringbone and spherulite textures emerge due to spontaneous nematic (N) to columnar M-phase transition, propagating from the LCLC-PDMS interface into the LCLC bulk. By varying the confinement geometry, anchoring conditions, and the initial DSCG concentration, we can systematically tune the temporal dynamics of the N- to M-phase transition and textural behavior of the confined LCLC. Overall, the time taken to change from nematic to the characteristic M-phase textures decreased as the confinement aspect ratio (width/depth) increased. For a given aspect ratio, the transition to the M-phase was generally faster in degenerate planar confinements, relative to the transition in homeotropic confinements. Since the static molecular states register the initial conditions for LC flows, the time dependent textures reported here suggest that the surface and confinement effects—even under static conditions—could be central in understanding the flow behavior of LCLCs and the associated transport properties of this versatile material.
Highlights
Lyotropic chromonic liquid crystals (LCLCs) are a class of lyotropic liquid crystals (LCs) that are formed by anisotropic assemblies of water-soluble disc-shaped molecules which have an aromatic core surrounded by ionic groups
The nematic phase consists of short columnar stacks of disodium cromoglycate (DSCG) molecules and appears at room temperature for low DSCG concentrations, whereas with the increase in DSCG concentration, the stacks assemble into a two-dimensional hexagonal array of extended columns in the M-phase [5,6,7], archetypal herringbone and spherulite textures spanning a wide range of concentration and temperature conditions
We present the dynamics of the emergence of the LCLC textures due to the DSCG solution
Summary
Lyotropic chromonic liquid crystals (LCLCs) are a class of lyotropic liquid crystals (LCs) that are formed by anisotropic assemblies of water-soluble disc-shaped molecules which have an aromatic core surrounded by ionic groups. Unlike lyotropic LCs, LCLCs do not form micelles; rather, they stack up as linear aggregates, held together by non-covalent interactions which lead to self-assembled nematic (N) phase or columnar (M-phase) with a hexagonal arrangement [1,2,3,4]. In both the N- phase and the M-phase, the director is parallel to the columnar axis of the stacks, as was revealed by X-ray studies. LCLCs have been explored as host systems for active bacterial systems [11,12]
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