Thermodynamical, optical, dielectric and electro-optical characterisation of nematic liquid crystals (LCs) and silver nanoparticle (NP) composites have been carried out. Transition temperatures of pure and composites systems have been measured. Thermodynamical studies suggest increase of clearing temperature of the composite material as compared to the pure material. Threshold voltage for switching from bright to dark state and splay elastic constant of the pure and composite materials have been determined. From frequency dependence of dielectric measurements, permittivity, loss, relaxation frequency and dielectric strength of flip-flop mechanism of LC molecules in the nematic phase have been calculated. Dielectric properties of composites have been explained in reference of Maier and Meier theory. The effects of doping of NPs on dielectric and electro-optic properties of LC-NP composites have been discussed.

We report electro-optical and dielectric studies of the gold nano particle (GNP) dispersed room-temperature liquid crystalline material 4′-pentyl-4-cyanobiphenyl (5CB) at a concentration of 0.1 wt%. Due to the dispersion of GNPs, the nematic to isotropic transition temperature is significantly increased. The threshold voltage required to switch molecules from the planar orientation (bright state) to the homeotropic (dark state) orientation is decreased. The dielectric parameters, namely, the longitudinal component of the dielectric permittivity and hence the dielectric anisotropy, are highly affected. The relaxation frequency corresponding to flip-flop motion of the 5CB molecules about their short axes has increased due to the presence of GNPs.

Composites of nematic liquid crystals (NLCs) and ferroelectric barium titanate (BaTiO₃) nanoparticles (NPs) have been prepared. The alignments of NPs in the host medium have been demonstrated. Effect of NPs doping on various display parameters of NLCs, namely, threshold voltage, dielectric anisotropy and splay elastic constant has been studied using electro-optical and dielectric studies. The nematic ordering of host supports alignment of NPs parallel to the director which consequently improves electro-optical parameters in the composite system. The dielectric and electro-optic properties of LC–NPs composites have been discussed in frame of conventional theories of NLCs.

Employing thermodynamical, optical and comprehensive dielectric studies, we have investigated a freshly synthesized chlorinated MHPOBC analogue antiferroelectric liquid crystal; it exhibits different chiral SmC sub-phases, viz. SmC_α*, SmC* and SmC_γ*, at considerably lower temperature in comparison with MHPOBC, and a wide range room temperature antiferroelectric SmC_A* phase. Dielectric spectroscopy investigations under planar molecular anchoring were carried out in the frequency range 1 Hz to 10 MHz. The data measured for low and high frequency regions were corrected by the method of fitting operation of the theoretical equations. Seven different modes of dielectric relaxation in the different phases were identified. Soft mode relaxation was identified in the SmA* and SmC_α* phases. The Goldstone mode, characteristic of the ferroelectric phase, was observed in the SmC* and SmC_γ* phases. Two characteristic peaks are seen in the spectrum of the SmC_A* phase: one, at high frequency, corresponds to fluctuation where the molecules in neighbouring layers are rotating in opposite phase; the other, at low frequency, arises due to phase fluctuation in the helicoidal superstructure.