Grain boundary phenomena in soft photonic crystals of liquid-crystalline blue phase II

This work investigated tilt grain boundaries in soft simple-cubic photonic crystals of blue-phase liquid crystals (BPLC). With precisely controlled shape and orientation of crystal grains, we examined how the misorientation angle and boundary orientation affect the grain-boundary morphology. Observations include smooth lattice deformations, planar defects, and the formation of new grains. We also explored the dynamic response of grain boundaries to external stimuli. When heated or subjected to an electric field, these grain boundaries can undergo premelting, lattice reconfiguration, or surprising long-range interactions (with defects propagating almost unidirectionally over distances of $\sim \text{3,000}$ times the lattice constant, linking two grains). Our findings provide new insights into mesoscale interactions in soft BPLC crystals and inform the design of BPLC-based optical elements and photonic devices that rely on spatially varying lattice orientation.