A dispersion of colloidal gold nanoparticles (GNPs) in a triphenylene-based discotic liquid crystal (DLC), namely 2,3,6,7,10,11-hexabutyloxytriphenylene (HAT4), possessing a hexatic plastic columnar phase (Col_hp) phase, has been studied by differential scanning calorimetry, polarized light microscopy, UV-Vis absorption spectroscopy, X-ray diffraction and dielectric spectroscopy. GNPs have been dispersed at three different concentrations in pure HAT4 viz. 0.2, 0.6 and 1.2 wt%. It has been observed that with the increase of GNPs concentration, the Col_hp–isotropic liquid transition temperature decreases substantially but the crystal–Col_hp transition temperature does not changes significantly. Electrical conductivity increases by at least five orders of magnitude for the highest concentration of GNPs (1.2 wt%) as compared to the pure material i.e. HAT4. Observed results suggest that although extremely low concentrations of GNPs are not very useful, a moderate concentration is highly useful for increasing the conductivity of the Col_hp phase and also to implant surface plasmon resonance. These results may be exploited to enhance the efficiency of electro-optical devices by using HAT4–GNPs composites.

Thermodynamical, dielectric, optical and electro-optical characterisation of pure 8CB and its composites with gold and silver nanoparticles have been studied. Thermodynamical studies suggest a decrease in clearing temperature of the nanocomposite systems as compared to the pure system. Dielectric parameters of pure nematic liquid crystal and nanocomposites in the homeotropic and planar aligned samples have been measured in the frequency range of 1–35 MHz. Ionic conductivity increases significantly in nematic and smectic A_d (SmA_d) phases, whereas dielectric anisotropy is almost unchanged for both the nanocomposites. Threshold voltage for Freederick transition, switching voltage and splay elastic constant have decreased in the case of nanocomposite systems. Relaxation frequency and activation energy of an observed relaxation mode corresponding to molecular rotation about the short axis increase in the SmA_d phases of both the nanocomposites. The optical study suggests that due to dispersion of nanoparticles, the optical band gap has decreased.

In the present work, single-walled carbon nanotubes (SWCNTs) were dispersed in a room temperature nematic liquid crystal 4-pentyl-4′-cyanobiphenyl at the concentration of 0.02 and 0.05 wt%. Differential scanning calorimetry and temperature-dependent dielectric studies suggest decrease in clearing temperature of the composite materials as compared to the pure material. Ionic conductivity increases by two orders of magnitude due to the dispersion of such a low concentration (0.05 wt%) of SWCNTs. Dielectric studies also show that the presence of the SWCNTs decreases the effective longitudinal as well as transverse components of the dielectric permittivity. For homeotropic aligned samples, a relaxation mechanism has been detected in the lower MHz region both for the pure as well as dispersed samples. Presence of SWCNTs increases the relaxation frequency corresponding to flip-flop motion of molecules around their short axes. From frequency-dependent dielectric studies, important dielectric parameters such as relaxation frequency, dielectric strength and distribution parameters have been determined. Electro-optical experiments show that the threshold voltage decreases and the steepness of the transmission voltage curve improves due to the dispersion of SWCNTs.