Time dependent lyotropic chromonic textures in PDMS-based microfluidic confinements

Nematic and columnar phases of lyotropic chromonic liquid crystals (LCLCs) have been long studiedfor their fundamental and applied prospects in material science and medical diagnostics. LCLC phasesrepresent different self-assembled states of disc-shaped molecules, held together by noncovalentinteractions that lead to highly sensitive concentration and temperature dependent properties. Yet,microscale insights into confined LCLCs, specifically in the context of confinement geometry andsurface properties, are lacking. Here, we report the emergence of time dependent textures in staticdisodium chromoglycate (DSCG) solutions, confined in PDMS-based microfluidic devices. We use acombination of soft lithography, surface characterization and polarized optical imaging to generateand analyze the confinement-induced LCLC textures, and demonstrate that over time, herringboneand 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 confinementgeometry, anchoring conditions and the initial DSCG concentration, we can systematically tune thetemporal dynamics of the N to M-phase transition and textural behaviour of the confined LCLC. Sincestatic molecular states register the initial conditions for LC flows, the time dependent boundary andbulk conditions reported here suggest that the local surface-mediated dynamics could be central inunderstanding LCLC flows, and in turn, the associated transport properties of this versatile material.