Effect of alumina nanoparticles on dielectric permittivity, electrical conductivity, director relaxation frequency, threshold and switching voltages of a nematic liquid crystalline material

In the present work, alumina (Al2O3) nanoparticles (Al-NPs) were dispersed in a room temperature nematic liquid crystal 4-pentyl-4MODIFIER LETTER PRIME-cyanobiphenyl (5CB) at the concentrations of 0.2 and 0.6wt%. Differential scanning calorimetry studies suggest decrease in clearing temperature of the composite materials as compared to the pure material. Dielectric studies show that the presence of the Al-NPs decreases the effective longitudinal component ( [GRAPHICS] ) of the dielectric permittivity while has no effect on the transverse component ( [GRAPHICS] ). Ionic conductivity decreases for low concentration of the nanoparticles. In the case of homeotropic aligned samples, a dielectric relaxation mode has been detected in the MHz frequency region. Presence of the Al-NPs decreases the relaxation frequency corresponding to flip-flop motion of molecules about their short axes. From the frequency-dependent dielectric measurements, important dielectric parameters have been determined. Electro-optical experiments show that the threshold voltage decreases and the steepness of the transmission-voltage curve improves due to dispersion of Al-NPs.