Satya Prakash Yadav

Effect of TiO2 nanoparticles dispersion on ionic behaviour in nematic liquid crystal

The present study focuses on the ionic behaviour in nanoparticles (NPs) dispersed nematic liquid crystal. Dielectric spectroscopy has been used to investigate the behaviour of ions in suspension of NPs and liquid crystal (LC). Ionic concentration, diffusion coefficient, activation energy and mobility have been calculated from dielectric data. It is found that ion concentration increases initially and then it decreases with increasing concentration of NPs in suspension. The initial increase in ion concentration is attributed to the insertion of more ions due to impurities of TiO2 NPs and various other reasons. Temperature dependence of diffusion constant for different loading of TiO2 NPs is also investigated. The activation energy of NPs dispersed LC is found to be lower than the pristine one and it decreases with increasing concentration of NPs. The decreasing DC conductivity with increasing NPs concentration is attributed to the hindered or restricted motion of ions in the suspension. It is proposed that TiO2 NPs may be a potential candidate to be used to suppress the undesired ionic effect in LCs.

Effect of dye dispersion on the relaxation modes of smectic C* phase

We study how the dye dispersion influences the properties of ferroelectric liquid crystal (FLC). The polarisation measurement shows the decreasing linear behaviour with the increasing concentration of dye, indicating the orientation of dye in a direction opposite to FLC molecules. Accordingly, the response time increases with increasing concentration of dye. Dielectric data clearly show the existence of two relaxation phenomena in FLC and dye–dispersed systems. The relaxation strength of the Goldstone mode, which is observed around 200 Hz, has decreased with the dispersion of dye, and the relaxation frequency of this mode shifts towards the lower frequency side, due to increase in the rotational viscosity. The second relaxation mode, observed at ∼30 KHz, arises due to the formation of domains at the surface interface. This domain mode got suppressed with the dispersion of dye into FLC.

Guest–host interaction in ferroelectric liquid crystal–nanoparticle composite system

The present paper deals with the characterization of a ferroelectric liquid crystal–nanoparticle (FLC–NP) composite system. The dielectric, electrical and polarization property of the FLC–NP composite system have been studied as a function of temperature and frequency. Ferroelectric Cu-doped ZnO (Cu–ZnO) nanoparticles have been added to the pure ferroelectric liquid crystal (FLC) Felix 17/100. The nanoparticles are bigger in size as compared to FLC molecules; therefore, they distort the existing geometry of FLC matrix and set up an antiparallel correlation with the dipole moments of the host FLC molecules. This antiparallel correlation of guest–host geometry reduces the net ferroelectricity of the composite system and modifies all the physical properties of the pure FLC. The change in properties has been analysed and explained in the light of guest–host interaction.

Suppression of relaxation modes in dye dispersed SmC* phase

We report the results of dielectric and electro-optical properties of ferroelectric liquid crystal (FLC), Felix 17/100, exhibiting chiral smectic C phase and dye dispersed FLCs. The polarization measurement on pristine and dye dispersed FLC mixture shows decrease in the value of polarization, indicating the distribution of dye dipole in a direction opposite to the orientation of FLC molecule. The rotational viscosity also decreases accordingly as shown by the measurement of response time. Dielectric measurement shows existence of two relaxation modes both in pure FLC and dye dispersed FLC. The relaxation strength of Goldstone mode decreases with the dispersion of dye and the relaxation frequency of this mode shifts towards the high-frequency side. The second relaxation mode arises due to the formation of domains at the surface interface. The dispersion of dye into FLC suppresses the domains.

Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal

ABSTRACT The present work concerns with the investigation of the effect of dispersion of Silica (SiO2) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO2 NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO2 NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation Ps and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions. Graphical Abstract

Suppression of Surface Domains in Ferroelectric Liquid Crystals by Dye Dispersion

The effect of dye dispersion on the surface domain formation at the interface of alignment layer and ferroelectric liquid crystal molecules has been studied. The observed dielectric data clearly shows the existence of two relaxation modes in ferroelectric liquid crystal. The relaxation, which shows its contribution in KHz region, takes place due to the formation of domains at surface interface. In both the cases i.e. dye dispersion in Felix17/100 and in DOBAMBC, relaxation strength decreases with dispersion of dye, indicating the suppression of domains. Relaxation frequency in case of Felix 17/100 decreases while it increases for DOBAMBC with the dispersion of dye. The suppression of these surface domains are beneficial from the application point of view, as these domains are responsible for the scattering of light and suppression of these domains will increase the contrast and brightness of the display.