Plant-Mediated ZnO Nanoparticles as Functional Additives for Enhancing the Dielectric and Optical Response of Nematic Liquid Crystal

<title>Abstract</title> <p> The present work investigates the influence of green-synthesized ZnO nanoparticles (NPs) derived from <italic>Caesulia axillaris</italic> Roxb. leaf extract, on the optical and dielectric parameters of a thermotropic nematic liquid crystal (NLC), namely 4′-heptyl-4-biphenylcarbonitrile (7CB). Synthesised NPs were characterised by UV-Visible spectroscopy analysis, which confirmed a band gap of 3.13 eV, while X-ray diffraction (XRD) observed an average crystallite size of ~ 5.41 nm. Moreover, FESEM and HRTEM investigations provided detailed insights into the structural morphology. To investigate their effect on NLC behaviour, 0.5 wt.% of ZnO NPs were dispersed in 7CB (4′-Heptyl-4-biphenylcarbonitrile) NLC and optical and dielectric properties were examined for the resulting LC nanocomposite. Temperature controlled polarised optical microscopic study demonstrated an increase in isotropic temperature (T _N−I ) of 0.5 wt% ZnO NPs-7CB composite by 3.9% indicating enhanced molecular interactions between 7CB molecules and ZnO NPs resulting in improved orientational ordering. Dielectric spectroscopy results revealed a substantial enhancement in dielectric permittivity value by ~ 67%, as compared to pristine 7CB. The LC nanocomposite also showed reduction in dielectric loss, suggesting lower dielectric energy dissipation and better molecular polarization. Further, zeta potential and photoluminescence measurements revealed improved stability and modified electronic interactions in the LC nanocomposite system. Overall results demonstrate enhanced dielectric anisotropy, improved molecular ordering, and increased stability of the nanocomposite highlighting its potential for applications in advanced liquid crystal displays, photonic devices, and electro-optical technologies. </p>