(490b) Flow Behavior of Chiral Liquid Crystals

Microfluidic technology endows a suitable platform for scrutinizing the effect of various flow forces on the configurational evolution of complex fluids such as chiral liquid crystals and blue phases. Blue phases (BPs) are high chirality liquid crystals in which the liquid crystal molecules self-organize into double twisted cylinders (DTCs). DTCs can then self-assemble into three-dimensional cubic lattice structures capable of reflecting visible light. Here, we study the effect of shear and extensional forces on the orientational structures and phase transitions of two low and high chirality liquid crystals in microfluidic devices. A cylindrical capillary and a flow-focused capillary are used to generate shear flow and extensional deformation, respectively. Our rheological and flow-induced birefringence results, complemented by computational simulations, show that the coupling of helical organization and shear flow in a circular capillary gives rise to striking rheological behaviors in the low chirality liquid crystal associated with the director orientation, flow parameters, and channel dimensions. While a high level of shear forces can align the individual chiral liquid crystals, lower flow rates can drive the formation of the DTC structures. On the other hand, in the flow-focused capillary device, where the extensional flow drives the droplet formation, we observe a significant decrease in the transition temperature of the BP droplets. The transition temperature drop in the BP droplets is strongly droplet size-correlated; the smaller the droplet size, the lower the transition temperature. These findings can pave the way to new strategies in designing applications based on the combination of liquid crystal microfluidics and optics, such as advanced displays and tunable filters.