Engineering Topological Structures in Nematic Liquid Crystals for Functional Applications

Topological structures in nematic liquid crystals (LCs) emerge because of spontaneous symmetry breaking or geometric frustration under specific boundary conditions during the alignment of LC molecules. Historically, these topological structures have been regarded as defects that should be eliminated in the display industry. However, by precisely controlling the topological structures of LCs and utilizing the resulting elastic energy landscapes and physical anisotropy, they can be used not only to model other physical systems but also as functional materials. As a result, the topological structures of LCs have attracted significant attention in condensed matter physics, photonics, and materials science. This Review introduces the underlying principles of topological defects and solitons emerging in nematic and chiral nematic LC systems, comprehensively discussing engineering strategies for their precise manipulation. Building upon these foundations, a broad spectrum of innovative applications, such as colloidal self-assembly, soft actuators, tunable optical and photonic devices, and hardware security systems, have been highlighted. Finally, an outlook is provided for the realization of next-generation functional devices and active metamaterials.