Multistable polar textures in geometrically frustrated nematic liquid crystals
The ability to manipulate polar entities with multiple external fields opens exciting possibilities for emerging functionalities and novel applications in spin systems, photonics, metamaterials, and soft matter. Liquid crystals (LCs), exhibiting both a crystalline structure and liquid fluidity, represent a promising platform for manipulating phases with polar molecular order, notably ferroelectric ones. However, achieving a polar symmetry is challenging with rod-shaped LC molecules, which form predominantly apolar nematic phases. We report an approach in which a geometric lattice confinement of nematic LCs is used to induce planar polar order on the scale of a mesoscopic metamaterial. We confine the nematic LC in a micropillar array, forming topological defect-pillar pairs of elastic dipoles with a free top interface in contact with an immiscible fluid. The resulting dipole lattice configurations can be programmed rheologically by flowing the top fluid and maintained even after flow cessation, a phenomenon attributed to orientational multistability of the dipoles. This multi-memory effect enables the encoding and reconfiguration of directional information. Overall, this research establishes a foundational understanding of topological dipoles under confinement and shear flow, enabling the detection, tracking, and recording of flow profiles and paving the way for future advances in soft matter physics and stimuli-responsive materials.