Order Parameter Measurements Of Dichroic Dyes Dissolved In Smectic Liquid Crystals That Tilt Without Layer Contraction

Measurements of the orientational order parameter of dissolved dichroic dyes are reported for two smectic-A liquid crystals that tilt in the presence of an in-plane electric field without any decrease in the layer spacing. The dye order parameter is determined by measuring the anisotropic absorption of linearly polarized light. Different dyes are used and measurements are also performed on a smectic liquid crystal that tilts with the expected layer contraction to check how closely the measurements reflect the order parameter of the liquid crystal. The variation of the dye order parameter with electric field is in accordance with the recently proposed model of azimuthal disorder of the tilt angle direction, but the surprising finding is that the local dye orientational order parameter is significantly lower than for the smectic liquid crystal that tilts with the expected layer contraction. This suggests that another mechanism might be contributing significantly to the smectic order, one possibility of which is the tendency for different parts of these siloxane-containing molecules to segregate within each layer. Another possible explanation is that the azimuthal disorder is due to a modulated phase with a high enough density of defects to decrease the value of the local order parameter

Thickness dependent studies of hetero-junction solar cell synthesized on quartz substrate by spray pyrolysis technique

36-43Variable thickness hetero-junction solar cells synthesized on quartz substrate by spray pyrolysis technique synthesized quartz based solar cells have been found to possess cell parameters such as open circuit voltage, saturation current density, fill factor and efficiency in the range of 191 – 449 mV, 2×10-9 – 0.11×10-6 A cm-2, 15 – 20 % and 0.2×10-9 – 3.35×10-6 % at 206 mW/cm2 (at air mass 5.6), respectively. Series and shunt resistance of the solar cells have been found to vary with the thickness of semiconductor films. Thick film solar cells are found to possess reasonably good cell parameters compared to thin film solar cells due to enhancement of charge concentration, mobility, grain size, variation of optical band gap, excesses atomic percentage of Ti, Cu, Te, Sn elements in TiO2, CuO, CdTe, SnS films and less structural defects, increment of activation energy as well as existence of mixed phase at the Schottky barrier. The optical response of hetero-junction solar cells is found to be thickness dependent. Good rectifying characteristic has been reported in the present work for both thick and thin hetero-junction solar cells. All the measurements have been performed in air without protection against oxygen gas or moisture, which shows the stability of spray pyrolyzed thin films

Influence of Various Alcoholic Solvents on Structural, Morphological and Compositional Properties of Sprayed TiO2 Films

Titanium oxide thin films were prepared using solutions of titanium (IV) isopropoxide, acetyl acetonate dissolved in various alcoholic solvents such as methanol, absolute ethanol, 1-butanol, 2-butanol, 1-propanol, 2-propanol and tbutanol in the volumetric ratio’s of 1:1.5:22.5 by spray pyrolysis technique at substrate temperature of 350ºC under optimum conditions. The films have uniform thickness varying from 0.8–0.9 µm and good adherence to the substrate. XRD studies show poly crystalline nature of films. The Crystallite size (D), microstrain (e) and dislocation density (d) values varied from 96–289 nm, 1.25–3.75 10-4 lin-2m-4 and 1.2–10.76 1013lin m-2 respectively. Increase of microstrain, dislocation density and anatase to anatse-rutile mixed phase change may be attributed to increase in the concentration of lattice imperfections, crystallization of amorphous TiO2 films and long carbon chains in alcohol solvents. Present investigation reveals that alcohols play an important role in the crystallization of TiO2 layers. SEM micrographs exhibit spherical, square, needle shaped grains and grain boundary formation. Comparative study of SEM micrographs indicates variation of grain size from 0.1–0.7 µm. EDAX analysis shows the formation of stoichiometric TiO2 films, with an O-to-Ti atomic ratio of near 2 and variation of ratio as a function of various

Theory of melting of molecular crystals III: the effect of short range orientational order on liquid crystalline transitions

The theory of melting of molecular crystals developed in Parts I and II is extended to include short range orientational order. The thermodynamic properties are evaluated by the quasi-chemical method, which is mathematically equivalent to Bethe's treatment, and the theory is applied to liquid crystalline transitions. The interesting result is obtained that the nematic-isotropic transition is always first order, and that although the long range orientational order disappears suddenly at this transition point, a certain degree of short range orientational order persists in the isotropic phase. The specific heat exhibits both pre- and post-transition anomalies, in conformity with observations. The thermal expansion and isothermal compressibility show pre-transition anomalies but, contrary to experimental facts, no post-transition anomalies, indicating that even the quasi-chemical approach is not quite adequate for explaining all the properties

High pressure studies on HOAB: pressure dependence of the smectic C layer spacing

Using an opposed diamond anvil cell, an X-ray investigation has been made of the pressure dependence of the layer spacing in the smectic C phase of 4,4'-bis(heptyloxy)azoxybenzene (HOAB) up to 3.8 kbar. It is found that the layer spacing is independent of pressure to within the experimental limits. It is concluded therefore that the suppression of the smectic C phase of this compound at higher pressures is not due to a tilt angle variation with pressure

Monte Carlo Simulation of Smectic Liquid Crystals and the Electroclinic Effect: the Role of the Molecular Shape

Using Monte Carlo simulation methods, we explore the role of molecular shape in the phase behavior of liquid crystals and the electroclinic effect. We study a "bent-rod" mesogen shaped like the letter Z, composed of seven soft spheres bonded rigidly together with no intra-molecular degrees of freedom. For strongly angled molecules, we find that steric repulsion alone provides the driving force for a smectic-C phase, even without intermolecular dipole-dipole interactions. For weakly angled (nearly rod-like) molecules, we find a stable smectic-A (SmA) phase and a strong electroclinic effect with a saturation tilt angle of about 19 degrees. In the SmA phase we find evidence of vortex-like point defects. We also observe a field-induced nematic-smectic phase transition.Comment: 10 pages, including 10 postscript figures, uses REVTeX 3.0 and epsf.st

Smectic A1 — Smectic Ad Transition in Binary Mixtures of Compounds with Strongly Polar Terminal Groups

On the basis of high pressure studies we present here the evidence for the existence of a smectic A, — smectic Aj transition at high pressure in a binary liquid crystal mixture consisting of terminally polar compounds. A feature of this observation is that both the constituent compounds are three phenyl ring systems wherein the bridging dipoles are disposed additive with respect to the polar end group