Effects of CuInS₂ nanoparticles on the alignment control of liquid crystals

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.