Abhishek Kumar Misra

Zinc Oxide (1% Cu) Nanoparticle in Nematic Liquid Crystal: Dielectric and Electro-Optical Study

The present study reports the dielectric and electro-optical study of inorganic ZnO (Cu 1%) nanoparticles doped nematic liquid crystal (5CB). The dielectric permittivity is found to decrease in the nano doped sample. Nanoparticle doped liquid crystal has good response under various conditions to evaluate their potential as electro-optical materials for various purposes. From electro-optical study we have found Freedricksz transition voltage Vth and response time τ0 and hence K11 and rotational viscosity γ are also calculated. It is found that K11 and Vth increases for nano-doped sample. Rotational viscosity γ also increases for the nanoparticle doped sample. These changes have been explained in this article according to Osipov and Ternentjev theory of rotational viscosity of nematic liquid crystal.

Dielectric Relaxation of FLC Showing Anomalous Behavior

The present study reports the dielectric study of a ferroelectric liquid crystal (FLC) material Felix 016/030 showing anomalous dielectric behavior. This anomalous behavior is explained on the basis of a model of dynamically fluctuating mixture of two interconvertible conformers, whose relative density changes with the temperature. The dielectric permittivity has been measured in the frequency range of 100 Hz to 10 MHz in SmC* phase with the temperature variation from 25°C to 80°C. We have observed Goldstone mode of the dielectric relaxation in the frequency range covered. The Cole‐Cole equation has been used to analyze the relaxation phenomenon in FLC material under observation. The experimental results have been corrected for the low and high frequency range and used to determine various dielectric parameters such as distribution parameter, dielectric strength and relaxation frequency, and so on. The temperature dependence of these parameters along with rotational viscosity and spontaneous polarization extracted from Goldstone mode has been discussed in detail. The aforementioned dielectric parameters have also been studied with variation of bias voltage and it suggests that the Goldstone mode has been suppressed effectively by applying high bias voltage.

Dielectric and electro-optical parameters of two ferroelectric liquid crystals: a comparative study

Dielectric relaxation and an electro-optical study of two ferroelectric liquid crystals having different spontaneous polarizations (Felix 16/100 and Felix 17/000) showing SmC* and SmA phases have been performed in the temperature range 30?80?C. The experimental data have been used to determine different relaxation parameters, viz. distribution parameter, relaxation frequency, dielectric strength and rotational viscosity. The Goldstone mode of dielectric permittivity has been well observed for both the samples under investigation. The activation energy of both the samples has also been determined by the best theoretical fitting of the Arrhenius plot. We have also evaluated the optical response time and anchoring energy coefficients from electro-optical measurement techniques for these samples.

Electro-Optical Behavior for Dye-Doped FLC

The present study reports electro-optical parameters of two ferroelectric liquid crystals (FLCs) with the addition of anthraquinone dye D37 as a function of temperature. Accordingly, the parameters appearing in the switching model, the spontaneous polarization, switching time, and rotational viscosity have been determined by a well-established method. The values of electro-optical parameters show significant change due to the addition of dye. In addition to these parameters we have also evaluated anchoring energy coefficients. The polarization anchoring energy coefficients show decreasing trend and suggest that there must be lesser hindrance in plane switching of FLC molecules due to the addition of dye.

The molecular ordering phenomenon in dye-doped nematic liquid crystals

The experimental results of this work point out the role of the guest dye molecules in the molecular ordering of nematic liquid crystals. We have discussed the changes in the energies of interactions between rod-like nematic molecules and anthraquinone dye by considering the presence of steric and dipole–dipole interactions in the dye-doped system. The concentration of the dye plays an important role in the determination of molecular ordering in such dye-doped systems. Below a certain concentration of dye (known as the critical concentration), where the interaction between the dye molecules can be neglected, the addition of dye molecules introduces some disorder into the system in the form of domain formation. Above this critical concentration, this disorder is small.

Surface anchoring effect on guest–host ferroelectric liquid crystal response time – an electro-optical investigation

The effect is reported of surface anchoring on various electro-optical parameters of a pure ferroelectric liquid crystal (FLC) and five mixtures with different concentrations of dye. The Anthraquinone D5 dye was used as guest entity, whereas Felix 17-000 was used as host in this investigation. The presence of dye molecules in the FLC dramatically affects the electro-optical properties compared with those of the pure system. Electro-optical parameters such as spontaneous polarization and rotational viscosity not only change with the addition of dye but they are also strongly dependent on the concentration of dye in pure FLC. The effect of dye molecules on the anchoring energy of the pure FLC system was also investigated. Due to strong anchoring energy on FLC substrate, its effect on response time was also studied. An improvement in the contrast ratio after dye doping was observed. The value of spontaneous polarization increases due to addition of dye, suggesting that molecular alignment improves, which is very useful from the application point of view.

Dielectric relaxation study of a H shaped liquid crystal dimer

The present article reports dielectric relaxation study of an unusual shaped liquid crystal dimer (H shape) in the temperature range 40–85°C. The study of this liquid crystal dimer is important due to the presence of azo central linkage, which is photosensitive. The dielectric relaxation study indicates coupling between the electric field and the liquid crystal molecule of H shaped dimer. Various dielectric properties for this liquid crystal dimer are quite different from the conventional liquid crystals. The dielectric relaxation observed in the smectic phase is due to the reorientation of molecule along the director in the presence of an applied electric field. The temperature dependence of the dielectric parameters, such as relaxation frequency, relaxation strength and distribution parameter have been evaluated for this liquid crystal dimer for both planar as well as homeotropically aligned cell and then compared. The Cole–Cole equation has been used to evaluate the aforementioned parameters.

Dipole Dynamics of a Nano Doped Weakly Polar Liquid Crystal

The dielectric measurements of a weakly polarized nematic liquid crystal (D6AOB) were carried out in the frequency range 100 Hz to 40 MHz and in the voltage range from 0 to 40 V at 100 Hz. The dielectric data were measured for two principal alignments, homeotropic and planar. The angle β between the long molecular axis and dipole moment of the molecules is calculated from Cole-Cole plots using Onsager theory, both for pure and doped liquid crystal. Here is an attempt to discuss the Δϵ v/s voltage on the basis of piezoelectric strain, which is in good agreement with experimental results.

Electro-Optical Study of Fluorescent Dye-Doped Ferroelectric Liquid Crystal

The present paper reports the electro-optical behavior of a pure and fluorescent dye-doped ferroelectric liquid crystal (FLC) system. Different material parameters, such as spontaneous polarization and optical response time, have been analyzed by electro-optical study. The temperature dependence of these parameters have been discussed for the pure and the fluorescent dye-doped systems. The spontaneous polarization and optical response time have also been found to change strongly by the variation of concentration of the fluorescent dye into the pure FLC. In addition to these parameters, the present paper also reports the temperature dependence of the effective dielectric permittivity for the pure and fluorescent dye-doped FLC systems. The value of spontaneous polarization has improved after doping of fluorescent dye suggesting that fluorescent dye is beneficial for this FLC material.

Changes in material parameters for dye-doped ferroelectric liquid crystal

Addition of the dichroic anthraquinone dye molecules in pure ferroelectric liquid crystal (FLC) matrix results in many improvement in the various vital parameters of the pure FLC. However, addition of anthraquinone dye molecules in pure FLC matrix is not advantageous every time. There are certain constraints which are crucial for the application of these systems into many devices. In this article, we have discussed the concentration and temperature dependence of vital properties of dye-doped FLC. In this study there is improvement in contrast ratio by dye doping due to enhancement in plane switching for dye-doped FLC.