Liquid crystal-nanoparticle composite systems have attracted particular attention for both academic interests and applications in inducing macroscopic alignment, altering electro-optic response of the liquid crystal hosts, and generating ordered, tunable soft metamaterials. Herein, the synthesis of two shapes of CuInS₂ nanoparticles, tremelliform-like CuInS₂ and frame-like CuInS₂, and their utilization in producing uniform homeotropic alignment of liquid crystals are reported. Through exploring the mechanism in detail, the crystal structures of CuInS₂ nanoparticles were found to rely heavily on the reaction solvents during the growth process, which in turn play a significant role on the anchor of liquid crystal molecules. The achieved homeotropic alignment shows high thermal stability, owing to the outstanding stability of the CuInS₂ nanoparticles. In addition, combining this feasible method with parallel-aligning technique, variable pretilt angles in a range of ~ 0.9º to ~ 7.2º could be continuously achieved.

Excellent electro-optical (E-O) performances are essential for high-quality reflective cholesteric liquid crystal (LC) displays, but are often limited by the high driving voltages required by these displays. Dispersing functional nanomaterials into the LCs has emerged as a promising approach to achieve outstanding E-O properties. In this work, we report the facet-controlled E-O properties of a chiral nematic LC (N*LC) doped with cubic, octahedral, and rhombic dodecahedral Cu₂O. The outstanding E-O properties of the doped systems are related to the interaction between the liquid crystals and Cu₂O dopants with different exposed crystal planes. Doping with octahedral and rhombic dodecahedral Cu₂O reduces the stability of the planar state, as a result of both the surface abundance of active Cu atoms that interact with the polarized LC molecules, and the large amounts of vertexes and edges on the crystal surfaces, which accelerate the transition from the planar to the focal conic state under an applied electric field. Rhombic Cu₂O is the most effective dopant for improving the E-O properties of the present LCs, resulting in a 65.31% reduction of the threshold voltage. The facet and morphology effects highlighted in this work provide a new pathway to develop excellent energy-saving meso-materials with exposed high-reactivity facets, improving their potential applications in electro-optical technologies and information displays.

Nanoparticles (NPs) with flower-like and frame morphologies were synthesized from CuS, a remarkable transition-metal sulfide. We introduced two kinds of CuS NPs into a nematic liquid crystal (LC) 4-cyano-4'-n-pentylbiphenyl (5CB) and investigated the morphology- and concentration-dependent alignment and electro-optic (E-O) effects of CuS NPs on 5CB. A trace amount of flower-like CuS NPs induced a uniform homeotropic orientation of LC molecules; this is attributable to the obtained desirable compact nanosheet structure. Moreover, both flower-like and frame CuS NPs induced a remarkable improvement in the E-O properties of 5CB, and the flower-like CuS/5CB system exhibited a better performance. The doped CuS NPs in the LC host suppressed the shielding effect and strengthened the electric field, resulting in outstanding E-O properties. At a doping concentration of 0.05 wt.%, CuS NPs were well-dispersed and achieved the optimum E-O performance. This study provides a novel method for inducing a uniform orientation and enhanced E-O properties of LC molecules by doping with extraordinary CuS NPs, leading to potential applications in establishing flexible LC displays.