Dielectric, electrooptic and viscoelastic properties in cybotactic nematic phase doped with ferroelectric nanoparticles

Abstract

Hydrogen bonded liquid crystal, possessing a wide temperature range of cybotactic phase was used as a matrix to disperse ferroelectric LiNbO3 nanoparticles at the concentrations from 0.5 wt.% to 3.0 wt.%. The influence of nanoparticles on the physical properties has been studied with the help of polarizing optical microscopy (POM), impedance spectroscopy and electro-optic measurements. POM investigation revealed a nematic droplet dispersed in the isotropic phase due to the addition of ferroelectric nanoparticles. The suppression of the polarization has been observed and explained by the occurrence of antiparallel dipole configuration. The isotropic-nematic phase transition temperature was decreased due to the reduction in the parameter order. The decreasing in dielectric anisotropy (∆ε), response time (τ) and in threshold Freedericksz voltage (Vth) was associated to the decrease in splay constant elastic (K11) and in the rotational viscosity (γ). The curves of ∆ε, Vth, τ, K11 and γ when NPs concentration increases, showed a minimum at the same concentration (c = 1 wt.%) allowing the determination of the optimal NPs concentration.