Anoop Kumar Srivastava

Optimisation of electrode structure to improve the electro-optic characteristics of liquid crystal display based on the Kerr effect

Liquid crystal displays based on the Kerr effect are emerging because of their attractive features, such as symmetric viewing angle, no need for alignment layer, and sub-millisecond response time. However, high operating voltage and low optical efficiency remain as challenges to be overcome. Here, we propose a new cell structure with a protrusion shape of electrode and a driving scheme using two transistors to reduce operating voltage and enhance light efficiency. Confirming simulation results are obtained.

Dielectrophoresis force driven dynamics of carbon nanotubes in liquid crystal medium

This work reports the translation motion of carbon nanotubes (CNTs) dispersed in nematic liquid crystal (NLC) under an ac electric field. This effect was studied for homogeneously and vertically aligned NLC cells driven by in-plane field and vertical electric field, respectively. Long axis of the CNTs is aligned along the liquid crystal director, and above the critical field, the director of the NLC is distorted due to translation motion of CNTs in NLC. The amplitude of this translation motion decreases with increasing frequency, whereas the critical field increases with increasing frequency. We present the mechanism of translation motion of CNTs and model this observed phenomenon based on dielectrophoretic force.

Unusual double four-lobe textures generated by the motion of carbon nanotubes in a nematic liquid crystal

Unusual double four-lobe nematic liquid crystal (LC) textures were observed in the carbon nanotube (CNT)-doped nematic LC under electric field. Through the electro-optical studies in a wide range of vertical electric fields in the direction of the long axis of the LC molecules, it was realized that the double four-lobe nematic LC textures were formed in the range of 120 to 160 V(rms) at 1 Hz. The formation of these unusual double four-lobe nematic LC textures could originate from the electric field-induced movement of CNTs and the subsequently frustrated reorientation of LCs.

Switching and electrical properties of ferro‐ and antiferroelectric phases of MOPB(H)PBC

Switching and dielectric relaxation phenomena were investigated for an antiferroelectric liquid crystal, 4,4‐(1‐methyloctyloxycarbonyl)phenyl]‐4′‐[3‐(butanoyloxy)prop‐1‐oxy]biphenyl carboxylate, exhibiting chiral smectic A (SmA*), smectic C (SmC*) and antiferroelectric (SmCA*) phases. Spontaneous polarisations, rotational viscosities, relaxation frequencies, dielectric strengths and distribution parameters were determined as a function of temperature. The electric field required for saturation of the spontaneous polarisation increased with a decrease in temperature. In the SmA* phase, only one relaxation mechanism was observed that behaves as soft mode. Two relaxation processes were detected in the SmC* phase. A high‐frequency relaxation process invariant at 2.2 kHz was due to a Goldstone mode, but the origin of low‐frequency relaxation process (1–20 Hz) is unclear; however, it may belong to an X‐mode. The dielectric spectrum of the SmCA* phase exhibits two absorption peaks separated by two decades of frequency. The low‐frequency peak is related to the antiferroelectric Goldstone mode, whereas the high‐frequency peak originates from the anti‐phase fluctuation of the directors in the anti‐tilt pairs of the SmCA* phase.

Switching of off-axis viewing quality in twisted nematic liquid crystal display by controlling phase retardation of additional liquid crystal layers

This study examined the viewing angle control of twisted nematic liquid crystal displays (TN-LCDs). Conventional TN mode has intrinsic characteristics, such as a narrow viewing angle along the vertical direction and a relatively wide viewing angle along the horizontal and diagonal directions. Our study shows that the viewing angle of the TN-LCD can be made wider and smaller than that of a normal TN cell by adding one or two homogeneously aligned liquid crystal layers between the TN cell and polarizers, and controlling their retardation with an applied voltage.

Carbon Nanotube Effects on Electro-Optic Characteristics of Twisted Nematic Liquid Crystal Cells

Twisted nematic (TN) liquid crystal (LC) cells doped with carbon nanotubes (CNTs) were fabricated and their electro-optic characteristics were studied. The CNTs with a minute amount of doping did not disturb the liquid crystal orientation in the off and on state. Effects of CNTs on voltage-dependent transmittance curves and voltage holding ratio were not found to be so strong. The response time however was improved as compared to pure LC.

P-132: Blue Phases Liquid Crystal Cell Driven by Strong In-Plane Electric Field

The polymer-stabilized blue phase liquid crystals are in the limelight of liquid crystal display area because of its fast response and wide viewing angle with alignment layer free. The conventional device is driven by in-plane field, which has thin electrodes only on bottom substrate and also due to low Kerr constant of LC, the driving voltage of the device is very high. We propose improved electrode structure which has partition-wall shaped electrodes. The proposed device has maximized horizontal electric field so that the driving voltage is decreased. Further, adoption of two transistors can lower driving voltage.

Surface Polymer-Stabilized Vertically Aligned Liquid Crystal Cells with Various Polymer Wall Structures

Vertically aligned liquid crystal (LC) surrounded by polymer wall, which is also known as locked-super homeotropic (LSH) mode has several advantages such as rubbing- and spacer-free, wide-viewing angle and stable LC dynamics against external pressure. However, the LSH mode shows slow response time due to the instantaneous collision between the LC molecules when a vertical electric field is applied, because the reorientation of chiral doped vertically aligned LC is only determined by the polymer wall. We found that the slow response time can be improved by surface polymer-stabilized technique where surface pretilt angle is defined on alignment layers. This technology can be used in any shape of polymer wall. (PACS 42.79.Kr, 85.60.-q).

Combustion synthesized Fe doped CeO2 powder-characterization, optical absorption and EPR spectroscopy

Fe doped CeO2 powder was prepared using solution combustion method. Powder X-ray diffraction and scanning electron microscopy methods are used to characterize the combustion derived powder. The optical absorption spectrum exhibits three bands due to Fe3+ and Fe2+ ions. Electron paramagnetic resonance (EPR) spectrum of this sample exhibits number of resonance signals due to Fe3+ ions. The number of spins (N) participating in resonance and its paramagnetic susceptibility (χ) has been evaluated. From EPR and optical studies it is observed that iron ions are present in trivalent state.

Negative dispersion retarder using two negative birefringence films

The achromatic response and wide viewing angle for varying wavelength of incident light are of long waiting research to be utilized it for the display devices. Such response can be obtained by employing the retarder that exhibits negative birefringence and negative dispersion. In this paper, negative dispersion half-wave retarder and negative dispersion quarter-wave retarder have been demonstrated by optimizing the retardation and the angle between the extraordinary axes of polystyrene and poly-methylmethacrylate films. The optimum angles for half and quarter-wave retarders were found to be 40° and 70°, respectively for different retardation values of polystyrene and poly-methylmethacrylate films.