Structures and topological defects in pressure-driven lyotropic chromonic liquid crystals

Area of Science:

• Soft Matter Physics
• Materials Science
• Fluid Dynamics

Background:

• Lyotropic chromonic liquid crystals (LCLCs) are water-based materials with self-assembled cylindrical aggregates.
• Understanding LCLC behavior under flow is crucial but limited by current imaging speeds.
• Optical retardance quantification in flowing LCLCs requires faster, high-resolution techniques.

Purpose of the Study:

• To quantify the spatial distribution and dynamics of structures in flowing nematic disodium cromoglycate (DSCG) solutions.
• To investigate the nucleation, growth, and dynamics of disclination loops in LCLCs under shear.
• To provide a comprehensive understanding of LCLC structure and dynamics in microfluidic flows.

Main Methods:

• Employed single-shot quantitative polarization imaging using polarized shearing interference microscopy (PSIM).
• Studied nematic disodium cromoglycate (DSCG) solutions in a microfluidic channel under varying shear rates.
• Combined experimental observations with simulation and scaling analysis.

Main Results:

• Observed nucleation of pure-twist disclination loops in the bulk flow across a range of shear rates.
• Found loops are elongated in the flow direction with a constant aspect ratio determined by splay-bend anisotropy.
• Demonstrated that loop size is governed by nucleation and annihilation forces, and fluctuations indicate DSCG tumbling.

Conclusions:

• PSIM enables rapid, quantitative analysis of flowing LCLCs and their emergent structures.
• Pure-twist disclination loops in DSCG are governed by anisotropic properties and force balances.
• This research enhances understanding of LCLCs in microfluidics, with potential for controlling biological systems or particle assembly.