Comparative Effects of ZnO and TiO₂ Nanoparticles on the Electrical, Electro-Optical, and Sensing Properties of High-Birefringence Nematic Liquid Crystals: A Critical Review

This critical review provides a comprehensive comparative evaluation of zinc oxide (ZnO) and titanium dioxide (TiO₂) nanoparticles (NPs) dispersed within modern high-birefringence (Δn) nematic liquid crystal (LC) hosts, marking a substantial paradigm shift from traditional low-birefringence matrices like EBCA. We evaluate how the intrinsic electronic configuration, spatial morphology, and surface charge properties of ZnO and TiO₂ nano-dopants differentially modulate the host's long-range orientational order, dielectric anisotropy, rotational viscosity, and threshold voltages. Crucially, this work integrates rigorous multi-spectroscopic and optical characterization methodologies—specifically Fourier-Transform Infrared (FT-IR) spectroscopy for order parameter determination, Ultraviolet-Visible (UV-Vis) spectrophotometry for band-gap and transmittance profiling, and Polarizing Optical Microscopy (POM) for phase transition kinetics and texture morphology mapping. Finally, the state-of-the-art applications of these hybrid colloidal suspensions are scrutinized across electrical modulation, advanced electro-optical shutters, broadband optical sensors, and emergent biomedical/interfacial diagnostic platforms.