Density and Ultrasonic Velocity Measurements in Hexyloxybenzylidene Phenylazoaniline

The temperature variation of density and ultrasonic velocity of the liquid crystal hexyloxybenzylidene phenylazoaniline are reported. The density across the smectic A—smectic B transition is more predominant than the other transitions. The density variation with temperature and the calculated thermal expansion coefficients suggest that the transitions isotropic liquid—nematic, nematic—smectic A and smectic A—smectic B are of first order. Anomalous behaviour of ultrasonic velocity is observed across the isotropic liquid—nematic transition and prominent dips in velocity are observed at the nematic—smectic A and smectic A—smectic B transitions. The adiabatic compressibility (β _ad ) Rao number (R _a ) and molar compressibility (B) are estimated using the experimental density and ultrasonic velocity.     

Influence of flexible chain,polar substitution and hydrogen bonding on phase stability in Shiff based (4)PyBD(4I)BrA-nOBA series of liquid crystals

Shiff based Linear Hydrogen Bonded Liquid Crystalline homologues, viz., (4)PyBD(4^I)BrA-nOBAs for n = 2,3,4,5,6,7,8,10,11 and 12 are synthesized. ¹H-NMR and ¹³C-NMR studies confirm the formation of HBLC and IR confirms the linear hydrogen bonding. Liquid crystal phase abundance, transition temperatures, enthalpy and order of transition are investigated by Polarized Optical Microscopy textural studies and Differential Scanning Calorimetry. Nematic, Smectic-A, -D, -C, B_hexatic, -B_Crystal, -F, -I and –G phases are identified. Large LC phase variances, viz., NAB_hexFG and NACFG are exhibited by intermediate chain length with n = 5 and 6. A-C transition exhibited unique II-order nature. II-order nature for G-Solid transition explained. Phase diagram drawn with flexible chain length infers INA, and ACF and CIF MultiCritical Points and Lifshitz behaviour. NA TriCiritical Point predicted in [3+7] binary. Influences of chain length, linear HB and end polar(-Br) substitution for LC phase stability are is discussed. Results of Phase stability are discussed in the wake of the body of the data and reports in other LCs. DSC enthalpy suggests for utility of intermediate and higher homologues for device savvy tilted Smectic LC phases.     

Phase Transition Studies of the Liquid Crystal Pentyloxybenzylidene Phenylazoaniline

Phase transition studies of the liquid crystal pentyloxybenzylidene phenylazoaniline are investigated with density and ultrasonic velocity measurements. The density variation with temperature confirms that the isotropic liquid-nematic, nematic-smectic A and smectic A-smectic B transitions are of first order. The temperature variation of ultrasonic velocity confirms all the phase transitions. The adiabatic compressibility (β_ad), Rao number (R_n) and Molar compressibility (B) are estimated from density and ultrasonic velocity.     

Behaviour of Ultrasonic Velocity in Cholesteric Liquid Crystals

Ultrasonic velocities (V) have been determined, employing a fixed path double crystal interferometer, in three cholesteric liquid crystals, namely cholesteryl propionate, cholesteryl laurate and cholesteryl myristate in their isotropic and anisotropic phases including the region of the phase transition. The variation of specific volume (v) is also studied in the same temperature range by a special dilatometer constructed for this purpose. Anomalous behaviour of ultrasonic velocity is observed near the isotropic-cholesteric phase transition in all three compounds. In the two polymesomorphic liquid crystals, namely cholesteryl laurate and cholesteryl myristate, contrary to the ultrasonic behaviour of cholesteryl stearate, prominent velocity dips are observed at cholesteric-smectic transition temperatures. The parameters adiabatic compressibility (β_ad) and molar sound velocity (R) are estimated and they are found to exhibit sudden jumps at cholesteric-smectic and isotropic-cholesteric transitions. The thermal expansion and temperature co-efficient of compressibility are found to show abnormal increase near the phase transition indicating the existence of large-magnitude pre-transitional effects near the phase transition. A comparative study of the ultrasonic behaviour of six aliphatic esters of cholesterol has shown that the magnitude of the velocity dip observed at the isotropic-cholesteric transition increased with increase of molecular weight and only cholesteryl acetate shows deviation.     

Investigation of Ultrasonic Velocity and Related Parameters in Liquid Crystalline Mixtures

Investigations of ultrasonic velocity, specific volume and related parameters were carried out in a mixture of p-n-butoxybenzylidene-p-chloroaniline (BBCA) and p-anisal-p-toluidine (pApT) at eight different concentrations. BBCA exhibits polymorphism with two smectic phases, viz., smectic B and smectic A, while pApT is non-mesomorphic. All the mixtures studied were nematic, the mesomorphism vanishes below 34.3 mole percent of BBCA. Specific volume showed a large increase in the vicinity of the phase transition and the ultrasonic velocity showed an abrupt minimum near the transition. The adiabatic compressibility showed a maximum near the phase transition. It was found that the dip in ultrasonic velocity, change in specific volume and the jump in adiabatic compressibility at the transition decreases with increasing concentration of the non-mesomorphic compound. The parameter, viz., molar sound velocity was also estimated. The coefficient of thermal expansion and adiabatic compressibility were also estimated and they were found to attain very high values near the phase transition. The experimental results are explained on the basis of de Gennes theory of pre-transitional effects generalized by Bendler. The critical exponents are estimated in the isotropic as well as in the nematic phases.     

Experimental investigation of phase transitions exhibited by symmetric liquid crystal dimers

As a part of our systematic study of phase transitions in liquid crystal dimers we report here the variation of density across the phase transitions Isotropic – Smectic A and Smectic A – Smectic F exhibited by the Schiff base liquid crystal dimeric compounds of α,ω‐bis(4‐alkylanilinebenzylidene‐4′‐oxy)alkane (m.OnO.m) homologous series. The compounds studied are 6.O5O.6 and 6.O6O.6. The compound 6.O5O.6 exhibits only Smectic A phase, whereas the compound 6.O6O.6 exhibits Smectic A and Smectic F phases. The density jumps and peak in thermal expansion coefficient at the transitions confirm the first order nature of the transitions with a smaller density jumps compared to the monomeric liquid crystals. The calculated pressure dependance of the transition temperatures using Clauasius‐ Clapeyron equation is also reported. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase Transition Studies in N(p-n-Heptyloxy Benzylidene)p-Toluidine, 70.1, Across I-N,N-SA and SA-SB Phases

The results of density and ultrasonic velocity variation with temperature in N(p-n-heptyloxy benzylidene)p-toluidine, HYBT, 70.1 exhibiting nematic, smectic-A and crystalline smectic-B phases, are presented. The isotropic-nematic, nematic-smectic-A phase transitions are found to be first order while the smectic-A crystal smectic-B transition is weak first order. The thermal expansion coefficient α computed from the molar volume data is presented. The molar sound velocity and molar compressibility of HYBT computed from the density and ultrasonic velocity data in isotropic phase are compared with the values of the other compounds in a homologous series. They are found to be in good agreement with theory.     

Influence of TiO2 and ZnO nanoparticles on orientational order parameter of LC compounds – An optical study

In the present paper ZnO and TiO₂ nano particles are dispersed in Cyano-biphenyl liquid crystalline compounds (n?=?7, 12). The thermal polarizing microscopy and differential scanning calorimetry techniques are employed to measure the transition temperatures. The Nematic transition temperatures are decreased by 2.34?°C and 1.53?°C in Heptylbiphenyl, 1.07?°C and 1.12?°C in dodecylbiphenyl compounds due to the dispersion of nanoparticles. The refractive indices and Newton’s rings methods are exploited to measure birefringence at different temperature in nematic phase. The orientational order parameters are estimated by finding the birefringence in perfect order. The orientational order parameter is increased in nanoparticles dispersed liquid crystals when compare to pure liquid crystalline compounds.     

An optical microscopy study of the biaxial ‐ calamitic nematic lyotropic phase transition

Lyotropic nematic textures are investigated, using optical microscopy, near the reentrant isotropic (I_RE) ‐ discotic nematic (N_D^‐) ‐ biaxial nematic (N_B) ‐ calamitic nematic (N_C⁺) ‐ isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol and D₂O. The N_B, intermediate phase between the two uniaxial nematic ones, is characterized by optical birefringence measurements. In this way, using a polarizing microscope and a colour CCD digital camera, the N_B – N_C⁺ phase transition is identified as well as the domain of the N_B phase and N_D^‐ – N_B transition point in accordance with optical birefringence data (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Mesomorphic Behavior of Calamitic Liquid Crystals with a Biphenyl Moiety

A new mesogenic homologous series having a biphenyl moiety has been synthesized by condensing 4-hydroxy-4′-nitrobiphenyl- and methoxy-substituted 4-n-alkoxy cinnamoyl chlorides, and their liquid crystalline properties have been studied. All the members of the series are enantiotropic liquid crystals. The methyl to n-pentyl derivatives exhibit both Smectic A (SmA) and Nematic (N) phases; the higher members, starting with the n-hexyl derivative show only a SmA phase. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits zig-zag pattern for Sm-N and N-Isotropic (Iso) transition temperature curves. The average thermal stability is compared with other related homologous series. The introduction of polar nitro group increases significant intermolecular force of attraction which stabilizes the molecular orientation. This results into the increase in the thermal stability of the system.     

Lanthanum fluorozirconate glasses

Investigations in the ZrF₄-BaF₂-LaF₃ ternary system show the existence of a vitreous area in the range: ZrF₄: 56–67%, BaF₂:25–36%, LaF₃:3–13%. For a standard glass of molar composition 0.62 ZrF₄, 0.30 BaF₂, 0.08 LaF₃, the refractive index is 1.5248 with the glassy transition occuring at 310°C and fusion occuring at 545°C.Quaternary glasses have been obtained by including a MF fluoride (M = Na or Li) with the previous ternary glass according to the formula: (0.62 – 0.4x)ZrF₄(0.30 –0.5x)BaF₂(0.088 – 0.1x)LaF₃xMF. Evolution of glassy transition, refractive index, density and molar refractivity is discussed in relation to the structural role of the Na⁺ and Li⁺ ions. In these zirconium fluoride glasses, lithium could act as a network former at low concentration and as a network modifier at higher concentration.     

Elasticity and Orientational Order in Some trans-p-n-Alkoxy-α-methyl Cyanophenyl Cinnamates

The splay (k ₁₁), twist (k ₂₂) and bend (k ₃₃) elastic constants determined by the Freedericksz method and the orientational order parameters (s) derived from optical measurements in the nematic phase of six homologues of trans-p-n-alkoxy-α-methyl cyanophenyl cinnamates (n OMCPC) are reported. The data close to the nematic-isotropic transition point (T _NI) are compared with T _NI and the heats of transition (ΔH). The temperature-variation of elastic constants is discussed in terms of existing theories. The pretransitional increase in the twist and bend constants near the nematic-smectic A transition point (T _NA ) of 10 OMCPC has also been analysed.     

Study of a new homologous series of liquid crystals: Isopropyl-p-(p/-n-alkoxy cinnamoyloxy) cinnamates

A new homologous series: isopropyl-p-[p^/-n-alkoxy cinnamoyloxy] cinnamates was synthesized and studied with a view to understanding and establishing the relation between liquid crystal property and molecular structure. Twelve homologues were synthesized. Methyl to butyl homologues are not liquid crystals, while pentyl, hexyl, heptyl, octyl, decyl, dodecyl, tetradecyl, and hexadecyl derivatives are enantiotropic liquid crystal in nature with nematogenic character. Smectogenic character is totally absent. A phase diagram is obtained by plotting a graph of transition temperatures versus number of carbon atoms is n-alkyl chain of left n-alkoxy terminal end group. Solid-isotropic or solid-nematic transition curve rises steeply from methyl to propyl derivatives and falls to pentyl homologue through butyl homologue, and follows a zigzag path of rising and falling values as the series is ascended. Nematic–isotropic transition curve shows descending tendency as series is ascended in a normal manner with exhibition of odd-even effect. Smectic mesophase does not appear even in the monotropic condition. Phase transition temperatures are determined by hot stage polarizing microscope. Analytical data support the structure of molecules. Texture of nematic mesophase is of threaded type. Mesomorphic properties are compared with structurally similar homologous series.     

A neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND2CD2COOD)3.D2SO4

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND₂CD₂COOD)₃.D₂SO₄ is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below T_C using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H‐bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long‐range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure.     

Effect of Halide Ions on the Electronic Conductivity in Calcium Borate Glasses

Some halogen-doped calcium borate glasses containing iron have been prepared according to the percentage molar composition [(30 – x) CaO · x CaX₂ · 10 Fe₂O₃ · 60 B₂O₃] and annealed. It is found that the conduction in the semiconducting glasses is mainly due to electronic conduction. The results show that the halide ions may be introduced as modifiers for CaX₂ concentration < 10 mol% (X >= F, Cl, and Br) but they are network formers at CaX₂ > 10 mol%. It is proposed that at 10 mol% the network structure for all glasses seems to be the same. The dependence of resistivity on the halide ions concentration as well as the slight variation of activation energies, could be explained on the basis of electron-lattice interaction. Mathematical expressions for fitting and describing the dependence of resistivity on CaX₂ concentration are deduced and formulated by the following equations: ϱ = ϱ₀ exp [± ac(1 – bc)] and ϱ ϱ= ±₁₀ exp [± a′c(1 – b′c)] for the two regions around the critical concentration.     

Development of performance‐improved global positioning system (GPS) patch antenna based on sol‐gel‐synthesized dual‐phase (Bi4Ti3O12)X – (CaCu3Ti4O12)1–X composites

As a first attempt, a series of composite materials of general formula (Bi₄Ti₃O₁₂)_X – (CaCu₃Ti₄O₁₂)_1–X (BTO_X – CCTO_1–X) (X = 0–1.0) is synthesized by a sol‐gel combustion method. The phase changes, including their formation and evolution during the gradual substitution of BTO into CCTO are analyzed from the X‐ray diffraction pattern. The Jana2006 refinement plotting method proves that formation of an ideal dual‐phase composite system with separate orthorhombic and cubic phases occurs. A surface morphological study revealed that the BTO_X – CCTO_1–X composites are composed of small CCTO grains embedded in large BTO grains and both coexisted with a bimodal distribution. The possible vibrational modes of interactions between the constituent phases are determined from Raman spectra. Our inexpensive, combustion method for BTO_0.2 – CCTO_0.8 gives a high dielectric constant (ε′ = 3232) at 100 Hz at room temperature. The nature behind these data is revealed that the BTO‐CCTO composite can be applicable for the fabrication of miniaturized global positioning system (GPS) patch antennas. The fabricated GPS patch antenna shows optimum results of small size (2.37 mm × 1.18 mm), return loss (‐14.419) and wide bandwidth (350 MHz) to be operated at 1.57 GHz.     

Elastic and Optical Properties of Some 4′-n-Alkyl-4-Cyanobiphenyls

The bend elastic constants (k ₃₃) and order parameters (S) derived from optical measurements in the nematic phase of pentlyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) are reported. The odd-even effect is clearly seen in the K ₃₃ values of all four compounds and in the S values of the first three. 5CB, 6CB and 7CB show only the nematic mesophase but their elastic constants indicate the existence of smectic-like short range order. For example, even the lowest homologue, 5CB, does not obey the law k ₃₃ ∞ S ² given by the mean field throry. 7CB, has about the same order parameter as 5CB but a much higher elastic constant. 8CB, which shows a smectic A phase as well, exhibits a lower k ₃₃ than 7CB near the nematic-isotropic transition point but a pronounced pretransitional increase near the A-N transition.     

Optical and Electrooptical Properties of “Guest-Host” Effect in Twisted Liquid Crystal Layers

Abstract

Optical and electro-optical characteristics of a positive dichroic dye-doped Twisted Nematic Liquid Crystal Layer (TNLCL) for two different orientations of the input light polarization to the NLC director α (α = 0°, α = 90°) and various NLC optical path lengths A = Δnd/λ (Δn = real part of birefringence, d = cell thickness, λ = wavelength) are investigated. In the case of one polarizer, the maximum contrast ratio is obtained for A ? 1.2 (α = 0°) and A ～ 0 (α = 90°), regardless of whether Δn or d is changed. The viewing characteristics of a dye doped TNLCL with one polarizer are shown to be more uniform than those for a “pure” TNLCL between parallel polarizers.     

Compressibility in the Tetragonal Phase of AgInS2 From the X-ray Diffraction Data under High Pressure

The lattice parameters a and c as well as the compressibilities for different directions in the AgInS₂ chalopyrite-type compound are determined as a function of pressure up to 5 GPa using a powder X-ray technique under high pressure. It is found that the compressibility is anisotropic, with compressibility along the tetragonal c-axis (𝓏_c) being smaller than that along the a-axis (𝓏_a). It is shown that as pressure rises the axial ratio c/a increases and as a result the tetragonal distortion δ = 2 - c/a reduces.     

DSC characterisation of various phase transitions in mesomorphic benzylidene anilines

To analyse the order of the phase transitions in a number of mesomorphic benzylidene anilines, the DSC (Differential Scanning Calorimetry) method proposed by NAVARD and HAUDIN is used. This method involves the measurement of the ratio (N) of the DSC peak heights H₂/H₁ for a given transition, performed with two different heating rates (T₂/T₁). N is a function of the ratio r₂/r₁(= R) and the magnitude of N provides a simple way to characterize the order of a phase transition.