Recent advances and future perspectives on nanoparticles-controlled alignment of liquid crystals for displays and other photonic devices

Since their inception, liquid crystals (LCs) have been a topic of great interest among researchers around the globe. The alignment of LC molecules remains pivotal to explore the basic and applied aspects of LCs. Various alignment techniques such as rubbing of polyimides, coating of surfactants, magnetic field, oblique evaporation of SiOx, photoalignment, etc. have been widely explored to obtain the uniform alignment of LCs, eventually required in the fabrication of LC based displays and other photonic devices. One has to judiciously select the alignment technique to produce LC displays at industrial scale. However, certain issues have always remained which further stimulated the researchers to explore new sustainable ways of aligning LCs. Under this framework, the nanoparticles-controlled alignment could be one of new methods to align LCs. In this review, we have focused on the nanoparticles (isotropic and anisotropic) controlled alignment of LCs. The alignment of LCs could be achieved by: (i) doping of nanoparticles in the bulk LCs and (ii) patterning or growth of nanostructures on the substrates. Interestingly, the nanostructures grown on the non-conducting substrate are found to work as LC aligning agent and transparent conducting electrode. The nanoparticles doped polyimide alignment layers are also found to significantly improve the alignment of LCs. The quality of LC alignment obtained by using nanoparticles is more or less same as in conventional alignment techniques but less time consuming and cost-effective. Besides the induced or improved alignment of LCs due to nanoparticles, the electro-optical properties of LC devices are also found to be greatly improved as compared to devices using conventional alignment techniques. Moreover, we have discussed the pros and cons and future perspectives of nanoparticles tuned alignment of LCs.