(243i) Shear-Induced Instability of Blue Phase Liquid Crystals

Blue phase (BP) liquid crystals with a high level of chirality appear between chiral nematic and isotropic phases. In BPs, the anisotropic molecules form arrays of biaxial twisted structures called double-twisted cylinders (DTC). DTCs self-assemble into 3D cubic crystalline structures intertwined with the network of disclination lines arranged into body-centered cubic (BPI) and simple cubic (BPII) lattice symmetries. Here, we have studied the effect of shear flow forces on the arrangement of the disclination lines and the stability of the BP structures in bulk and within spherical microdroplets. The Linkam optical shearing system (CSS450) was used to apply continuous shear deformation to the BP bulk. Moreover, a lab-built microfluidic device was employed to explore the coupling of hydrodynamic forces and curved confinement on the structural reorganization and phase transitions of BPs within spherical droplets. Our results show that the shear deformation reduces the BP transition temperatures and stabilizes their structures at lower temperatures. In the flow-focused capillary microfluidic, on the other hand, the combined effect of shear flow forces and spherical confinement significantly enhances structural instability and temperature drops by about 20°C. This behavior is shear flow are and droplets size correlated; the higher the flow deformation and stronger the confinement, the lower the transition temperature. This phenomenon can be attributed to the extent of hydrodynamic forces acting on BP liquid crystals and the viscous dissipation heat. Understanding the structural transition of BPs in response to flow forces is interesting from a fundamental standpoint and has high practical applications.