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We have investigated the properties of liquid crystals (LCs) doped with ZnO (8% Cu doped) nanoparticles. The electro-optic properties of LCs have changed with varying concentration of ZnO nanoparticles. The dielectric anisotropy obtained from the values of dielectric permittivity at 5 kHz in the nematic and smectic phases was found to increase with increasing concentration of nanoparticles in LCs. It has been established that the effect of nanoparticles on the dielectric anisotropy depends on the physical properties of LCs; the nanoparticle disturbs the orientation ordering of LC molecules. The nanoparticle also influences the switching behavior, splay elastic constant, rotational viscosity and threshold voltage of pure LCs. A small quantity of nanoparticles causes slight reduction of the splay elastic constant and rotational viscosity of LC cells. IntroductionLiquid crystals (LCs) are a mesostate between solids and liquids. These share the anisotropic properties of optical (uniaxial and biaxial) crystals and the fluid properties of isotropic liquids [1,2]. These materials are extremely sensitive to the small external factors (electric and magnetic fields, surface effects, temperature, etc.) and possess order and mobility at microscopic and macroscopic levels [3]. The thermotropic LCs are technologically most important among all the LC mesophases, and the nematic mesophase is one of them which have broad applications in many engineering devices. Another important application of nematic LCs is their utilization in holographically formed polymer-dispersed LCs. These switchable diffraction gratings have broad engineering applications: video displays, switchable focus lenses, and photonic time-delay generators for optically assisted phased-array radars [3][4][5][6]. The remarkable advances in LC technology have led to the appearance of LC-based spatial light modulators (SLMs) and display applications [7]. The correct performance of all the above-mentioned devices requires LC materials that are stable over a long period of time, have high thermal stability and thermal range, high dielectric and optical anisotropy, and low switching voltage and switching times. These various requirements are achieved by using chemical synthesis and carefully designed mixtures of different LC materials such as dye, polymer, and nanoparticle [8,9]. It is important to note that in optimizing one property usually results in changes in other properties, mostly in an undesirable direction. Therefore, designing right materials for commercial applications is a challenging task.

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