Rajiv Manohar

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.

Single walled carbon nano-tube, ferroelectric liquid crystal composites: Excellent diffractive tool

We present a switchable grating based on chiral single walled carbon nano-tube (SWCNT) doped ferroelectric liquid crystals (FLCs). The presence of SWCNTs improves the diffraction profile of the pure FLC. The diffraction efficiency, i.e., the ratio of intensities of first order and zero order maxima is more than 100% for the higher concentration of SWCNTs in pure FLC. This phenomenon has been explained by the decrease in ferroelectric domain periodicity, due to the doping of SWCNTs in pure FLC, and optical activity of the chiral SWCNTs. These gratings with very high diffraction efficiency may find application in many devices.

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.

CdSe quantum dot-dispersed DOBAMBC: an electro-optical study

Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system.

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 Relaxation of Dye-Doped Ferroelectric Liquid Crystal Mixture: A Comparative Study of Smectic C* and Smectic A Phase

Present investigation reports dielectric relaxation behaviour of a ferroelectric liquid crystal mixture with and without doping of Anthraquinone dye. Dielectric properties of dye doped and pure ferroelectric liquid crystal mixture has been investigated as a function of temperature and frequency. In the present investigation Goldstone mode has been observed in smectic C* (SmC*) phase, while soft mode is observed in smectic A (SmA) phase and they have been explained with the help of Cole–Cole function. It has also been observed that the addition of dye strengthens the helix in SmC* phase, which is indicated by higher relaxation frequency and dielectric strength of the dye doped ferroelectric liquid crystal mixture. The SmC*–SmA phase transition point become sharper with the addition of dye in ferroelectric liquid crystal material and also shifted towards lower temperature side.

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.

Reduced ionic contaminations in CdSe quantum dot dispersed ferroelectric liquid crystal and its applications

Octadecylamine capped cadmium selenide quantum dots (CdSe QDs) were dispersed in the ferroelectric liquid crystal (FLC) FELIX 16/100. The QD dispersed FLC system was investigated on the planar anchored cell. Addition of specific concentration of the QDs in the pure FLC induces a new relaxation mode along with the Goldstone relaxation mode. QDs assisted quantum fluctuations are probably responsible for the existence of this new relaxation mode in the QDs dispersed FLC system. The ionic contaminations associated with the FLC materials were trapped on the surface of QDs due to the ion-trapping character of QDs. The trapping of ionic contaminations was confirmed by the a.c. conductivity measurement. The physical properties of the pure and dispersed FLC were carried out as a function of doping concentration of QDs, temperature and frequency.

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.

Cd1-xZnxS/ZnS core/shell quantum dot ferroelectric liquid crystal composite system: analysis of faster optical response and lower operating voltage

Cd1−xZnxS/ZnS core/shell-structured quantum dot (QD)-doped ferroelectric liquid crystal (FLC) Felix 17/000 has been investigated in the present study. In the SmC* phase, the effect of QD on the dielectric and electro-optical properties of FLC has been studied as a function of dopant concentration. A substantial change in the different parameters like tilt angle, spontaneous polarisation, response time and relative permittivity has been observed for the composite system. Nearly two times faster response of the composite system with lower operating voltage is one of the promising results of the present study. The faster optical response along with the decreased value of spontaneous polarisation can be utilised in low power consumption liquid crystal displays.