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

Abstract

In the present work, alumina (Al₂O₃) nanoparticles (Al-NPs) were dispersed in a room temperature nematic liquid crystal 4-pentyl-4ʹ-cyanobiphenyl (5CB) at the concentrations of 0.2 and 0.6 wt%. 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 () of the dielectric permittivity while has no effect on the transverse component (). 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.

Keywords:

• alumina nanoparticles
• dielectric permittivity
• relaxation frequency and transmission–voltage curve

Acknowledgement

NY thanks Mr Avneesh Mishra, Mr Mukesh Mishra and Ms Priti Yaduvanshi for their help during experiments.