Prasenjit Nayek

Tailoring Monodomain in Blue Phase Liquid Crystal by Surface Pinning Effect

Surface pinning effect of the optically isotropic, blue phase liquid crystal (BPLC) has been studied. Polycrystalline, platelet, multi-domain topological defects without surface treatment have been transformed to uniform monodomain in rubbed surfaces of the cell. The operating voltage was reduced by 27%, owing to a dramatic increase in the Kerr constant. Hysteresis was reduced by 63%, whereas the transmission efficiency gets doubled. The surface anchoring effect on the blue phase plays a significant role in the elastic free energy, coherence length and topological defects. BPLC displays with a low operating voltage, and reduced hysteresis can be realized with surface treatment.

Effect of the grain size on hysteresis of liquid‐crystalline Blue Phase I

— Three different blue-phase I liquid-crystal samples with different grain-size distribution were studied. Polycrystalline platelet grains reflects light in the visible region and have been observed under a polarizing optical microscope. Green and blue grain areas have been measured and then the statistical histogram by the Gaussian distribution function was fitted and the mean grain size was calculated. The effect of hysteresis on grain size has been compared for the three samples. Hysteresis depends explicitly on the grain-size distribution. Large grain size has revealed less hysteresis, while small grain size depicted pronounced hysteresis.

Optically isotropic liquid crystal mixtures and their application to high-performance liquid crystal devices

Optically isotropic liquid crystal (OILC) mixtures utilising polymerisation-induced phase separation in mixtures of prepolymers and liquid crystals (LCs) have been made and their overall electro-optic performances have been tested by applying an in-plane electric field for flexible display application. Excellent transparent films with a LC to prepolymer weight ratio of 42:58 are achieved and confirmed by SEM images. The average LC droplet size inside the polymer matrix is 215 nm. Consequently, an in-plane driven LC device with a crossed polariser shows a very high contrast ratio over 1000 comparable to the conventional nematic in-plane switching cell, wide viewing angle, a low threshold voltage of 8.2 V, hysteresis free and fast response time. The proposed LC device is free from an alignment layer and the rubbing process and its dark state is not disturbed by mechanical pressure, which can open its application to flexible liquid crystal displays.

Emergence of a novel optically isotropic transient state with low frequency in a blue phase liquid crystal mixture

The electro-optical hysteresis characteristics in a blue phase liquid crystal system showing multi-domain platelet type body-centred cubic (BP-I) structure at different levels of applied electric field have been investigated. The BP-I state possesses a large degree of hysteresis due to its compact body-centred cubic structure. The hysteresis behaviour is discussed in the context of simulation and theoretical studies reported earlier. When the cell is driven with a low frequency square wave, a novel optically isotropic state with high value of the Kerr constant has been observed. Hysteresis and response time both show relatively lower values in this state with respect to the multi-domain BP-I state.

Effect of cadmium sulfide nanorod content on Freedericksz threshold voltage, splay and bend elastic constants in liquid-crystal nanocomposites

This report describes how doping liquid crystals (LC) with rod-like hexagonal semiconductor nanoprisms alters the dielectric and elastic properties of the composites as compared with a pristine nematic liquid crystal (NLC). Cadmium sulfide nanorods were synthesized via the solvothermal process and blended with a NLC. Nanorods were highly miscible with NLC and produced a topological defect-free texture up to a certain limit. A good dark state was achieved during the homeotropic configuration of the cell within that limit. Appreciable changes in splay and bend elastic constants of the LCs were observed after blending with nanorods. Long-range order was established in the hybrid system, and consequently the anisotropy was increased. The threshold voltage decreased dramatically by ?31%. Dielectric study revealed a high-frequency mode, which might be due to anchoring of the LC with nanorods.

Study on the light leakage mechanism of a blue phase liquid crystal cell with oblique interfaces

The mechanism of light leakage in the dark state of a blue phase liquid crystal display cell which has protruded electrodes was investigated. We have performed a hybrid numerical simulation by combining the geometrical optics with the extended Jones matrix method. The light leakage in the cell was caused by changes in the polarization state which has been explained by the asymmetric amplitude change of transverse electric and transverse magnetic fields at the oblique interface and the change in an effective angle between crossed polarizers by the light path refraction. Based on our analysis, light leakage can be suppressed by the matching of the refractive indices of adjacent materials to the interface of the protruded electrodes whose surfaces are not parallel to the substrate.

Influence of Network Stabilization on the Dielectric and Electrooptical Properties of Ferroelectric Liquid Crystal FELIX-M4851/100

Dielectric and electrooptical properties as well as phase transition behavior in a network-stabilized ferroelectric liquid crystal were studied. The influence of polymerized network on these physical parameters were characterized. All measurements were performed upon adding monomer to the ferroelectric liquid crystal (FLC) mixture after in situ polymerization with UV radiation. We observed hysteresis-free symmetric V-shaped switching in a 2 µm cell. It was observed that both the Iso → N* and smectic A (SmA) → smectic C* (SmC*) phase transition temperatures were depressed to more ordered phase with increasing monomer concentration. The decrease was more prominent in the case of the SmA → SmC* phase transition. The Goldstone mode dielectric strength ΔeG in the SmC* phase was drastically reduced in the presence of networks. Soft mode dielectric strength was also reduced considerably. A small increase of pitch was observed with increasing monomer concentration. Spontaneous polarization was dramatically reduced in the presence of polymer networks.

Reduction of light leakage in protruded electrode by refractive index matching between protrusion and blue phase liquid crystal

We have studied the light leakage mechanism of the protruded electrode used for blue phase LCD. According to our study, the light leakage can be reduced by identical refractive indices of the protrusion and BPLC.

Hierarchical assembly of carbon nanotubes-liquid crystal nanocomposite.

Fabrication of liquid crystalline (LC) nanomaterials in an aligned pattern along the multiwalled carbon nanotubes (CNT) has been reported here. The nanocomposite was prepared by sonicating esterified CNTs and the ferroelectric liquid crystal (FLC) in chloroform. The nanohybrid shish kebab (NHSK) like pattern was observed in SEM analysis. The nanocomposite materials were characterized by Fourier transform infrared spectroscopy (FTIR), polarizing optical microscopy and electron microscopy. The DC and AC electrical properties of the composite materials were investigated. The DC conductivity of the nanocomposite increased by 2 order from the FLC materials and AC relaxation has been observed, in the nanocomposite, which was totally absent in the FLC materials.