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Incorporation of magnesium oxide nano particles (MgONPs) in a nematic liquid crystal display material namely 4-pentyl-4'-cyanobiphenyl (5CB) have been analyzed by differential scanning calorimeter, polarizing light microscopy and dielectric spectroscopy. MgONPs have been dispersed in two different concentrations in pure 5CB viz. 0.2 and 0.6 wt%. It has been experimentally noticed that with the increase of MgONPs concentrations in 5CB, the nematic to isotropic transition temperatures decreases and dielectric anisotropy increases. Relaxation frequency of an observed relaxation mode corresponding to molecular rotation about the short axis is almost unchanged after dispersion of MgONPs. The ionic conductivity has increased by approximately one order of magnitude for 0.6 wt% MgONPs and decreased for 0.2 wt%. [ABSTRACT FROM AUTHOR]

A vibrational spectroscopy study of a laterally fluorinated terphenyl liquid crystalline (LC) compound is presented in this paper. The study consists of temperature dependent Raman study and room temperature FTIR spectroscopy. The molecular structure was optimized using Density Functional Theory (DFT) with B3LYP functional and 6-31G (d, p) basis set and some structural properties have been noted. From the detailed study of the temperature dependent Raman spectra, the nature of the phase transition of the LC compound was investigated. It was found that the quadrant stretching modes and the CH bending modes of the phenyl rings display significant changes at Cr-N transition and N-I transition. This study therefore throws some light on the nature of transitions. From the FTIR study, it was found that the CC vibrations of the rings and NCS vibrations have large absorptions while the CH bending modes have less absorption. [ABSTRACT FROM AUTHOR]

Optical and X-ray studies have been conducted on a four component liquid crystal mixture (code name 2013) with cyano-end groups in all the four components and a lateral substitution of fluorine atom in one of them. The variations in the optical birefringence with temperature, have been investigated and the thermal dependence of polarisability anisotropy and orientational order parameter have been evaluated. X-ray studies have been conducted to determine the effective molecular characteristics such as apparent molecular length and inter molecular distance and their variations with temperature. From nature of molecular alignment as envisaged from X-ray photographs the order parameter variation with temperature has been determined and compared with macroscopic order parameter variation as determined from birefringence studies. The results have been compared with these obtained for another structurally similar four-component liquid crystal mixture (code name 2014) with isothiocyanato end group in place of cyano. [ABSTRACT FROM AUTHOR]

The aim of this present paper is to compare the effects of conducting polymer, poly (3,4-ethylenedioxythiophene) nanotubes and carbon nanotubes, on the electro-optical properties of a nematic liquid crystal mixture (1770-2). From the optical transmission and capacitance behavior it has been proved that the conducting polymer - nematic liquid crystal system possesses much lower threshold voltage and driving voltage than the carbon nanotube - nematic liquid crystal system which might be very useful in display applications. The effective elastic constant has been also significantly reduced in the conducting polymer - nematic liquid crystal system. [ABSTRACT FROM AUTHOR]

We have studied a compound (S)-(+)-4-(1-methylheptyl) 4-[4-(3-hexanoyloxyprop-1-oxy)benzoyloxy]biphenylate by means of differential scanning calorimeter, polarizing microscope and dielectric spectroscopy. This compound shows exceptionally a wide temperature range of [image omitted] phase ∼9°C together with a paraelectric SmA* phase. A relaxation mechanism in the high kHz region has been detected for the [image omitted] phase under planar orientation of the molecules. This mechanism has been characterized with temperature and bias electric field. Recent theoretical advances predict two different nature of dielectric relaxation mode in the [image omitted] phase (Phys. Rev. E, 69, 031709, 2004). Our experimental results confirm two different behaviors of this relaxation mode in different temperature range of the phase. [ABSTRACT FROM AUTHOR]

In this paper a tunable broad-band polarizer based on the photonic crystal fiber (PCF) filled with liquid crystal (LC) is presented. Host PCF is made of glass with 1.518 refractive index and ordinary refractive index of the LCs is lower than glass index. Numerical simulations have proven that by changing LC orientation from planar to transverse a broad-band single-polarization guidance is possible: for planar orientation of LC molecules both polarizations are index-guided, whereas for transverse orientation only one polarization is index-guided. Also some initial experimental results are included showing that polarization dependent losses and phase birefringence can be tuned with transverse electric field. [ABSTRACT FROM AUTHOR]

We have designed, synthesized, and evaluated the physical properties of some high birefringence (Δn) isothiocyanato phenyl-tolane liquid crystals. These compounds exhibit a Δn ≃ 0.48-0.52 at room temperature and wavelength λ = 633 nm. Laterally substituted short alkyl chains and fluorine atom both eliminate smectic phase formation and lower the melting temperature. Both the moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. Examples of the mixtures containing the described components are presented. [ABSTRACT FROM AUTHOR]

High birefringence (Δn > 0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time. In this paper, we report the mesomorphic and physical properties of several fluorinated NCS terphenyl single compounds and mixtures based solely on laterally fluorinated aromatic rigid core structures. The single compounds have Δn ∼ 0.35 in the visible spectral region and relatively low viscosity. In terms of applications, these compounds can be used as a dopant for enhancing the figure-of-merit of commercial mixtures for display applications. Or we can formulate high birefringence eutectic mixtures using solely NCS terphenyl compounds for near IR laser beam steering applications. [ABSTRACT FROM AUTHOR]

Three ring chiral esters, substituted laterally or not with a fluorine atom, having chiral terminal chain of the structure -COOC*H(CH3)C6H13, and achiral terminal chain alkylated CnH2n+1COO(CH2)mO- or partially fluorinated CnF2n+1COO(CH2)mO- (n = 1-7, m = 3-6) were measured by small angle X-ray scattering technique. Most of the fluorinated homologues have high tilted an orthoconic antiferroelectric phase (angle in neighbouring layers is around 90°), which is followed by a SmA phase of like de Vries type. The following parameters are compared: temperature function of d, dA, d/l, dA/l, (d-layer thickness, dA-layer thickness of SmA phase, l-molecular length) upon temperature and relation with the structure is discussed. The preferred structure for formation of the orthoconic antiferroelectric structure is partially fluorinated terminal alkyl chain and biphenylyl benzoate rigid core. The strongest de Vriesation of SmA phase is observed for longer fluorinated terminal alkyl chain (n > 4, m = 6) and phenyl biphenylate rigid core substituted by a fluorine atom in the 2 position of the phenyl ring. [ABSTRACT FROM AUTHOR]

We have developed some high birefringence (Δ n ∼⃒ 0.3 at λ = 633 nm) and relatively low viscosity nematic mixtures using isothiocyanato tolanes. These mixtures exhibit a high figure-of-merit (FoM) which is desirable for reducing the device response time. Using such a high FoM liquid crystal mixture in a 2-μm homogeneous cell, we demonstrate a 1π phase modulator at λ = 633 nm with submillisecond response time. [ABSTRACT FROM AUTHOR]

We have investigated the static and dynamic electrooptical effects of adding an alignment layer derived from a chiral liquid crystal having SmC* and N* phases to the standard polymer alignment layer in antiferroelectric liquid crystal cells. Our results show that the added layer reduces the relaxation time of the liquid crystal, the threshold voltage and the dynamic range required to generate a full greyscale. The electrooptical response of materials was tested using a 7 level waveform, and the relaxation was studied using a novel memory test. [ABSTRACT FROM AUTHOR]

The use of antiferroelectric liquid crystals(AFLCs)on practical applications is often precluded by their low contrast. Orthoconic AFLCs, in principle, may overcome this limitation, for they behave as isotropic plates at normal incidence. A number of orthoconic AFLC materials have been evaluated. Multiplexed seven-level driving schemes have been employed for dynamic analysis. The most relevant results include average static contrast ratio over 200:1 and dynamic contrast ratio over 130:1. On the other hand, hysteresis often shows slight voltage shifts when the cells are driven with low frequency AC signals. This feature impairs symmetry of the transmission maxima on the positive and negative lobes of the hysteresis curve. The effect is attributed to the extremely low pitch of actual orthoconic materials–usually below 1  μm. The distinctive properties of orthoconic materials make them suitable for photonic applications requiring moderate response time such as routing or beam steering applications. [ABSTRACT FROM AUTHOR]

Polymer-dispersed liquid crystals containing orthoconic antiferroelectric smectics were prepared by photopolymerization-induced phase separation. Mean droplet size allowed formation of antiferroelectric helix inside droplets. Bias electric field applied during phase separation aligned helical axes parallel to the cell plane. Obtained ellipsoidal droplets were optically uniaxial for perpendicular light beam. The cells were switched by square or triangle driving signal unwinding the helix. V-shape switching was found instead of threshold one observed in conventional cells of the same mixture. The switching time was crucially depended on temperature. Those effects were caused by anchoring conditions inside polymer cavities. [ABSTRACT FROM AUTHOR]

Addressing waveforms for reflective LCOS devices filled with V-shape chiral smectic liquid crystals, have been tested and optimised. Analogue greyscale generation has been tested on passive devices mimicking the behaviour in active matrix based devices. A comparative study of a number of experimental chiral smectic mixtures showing V-shape response has been carried out. Specific driving waveforms have been designed and optimised in order to improve the material's electro-optic response. This procedure is lengthy since every voltage level of the waveform ought to be separately optimised, and interdependences between the different waveform fragments lead to an iterative optimisation process. The effect of a short blanking pulse named well pulse has been particularly remarkable, thus forcing a thorough tune-up as a function of working temperature and video rate. [ABSTRACT FROM AUTHOR]