Dielectric Relaxation in Low Temperature Smectic Phases of 4-n-Alkyloxy-benzylidene-amino-4′-cyanobiphenyls

The dielectric behaviour of five homologous 4-n-alkyloxy-benzylidene-amino-4′-cyanobiphenyls was investigated. Especially, we were interested in the dielectric relaxation frequencies of the smectic low temperature phases S_B and S_E as well as the dielectric behaviour in the solid state. We have found in all liquid crystalline phases a low frequency relaxation region explained by a hindered rotation of the molecules around their short axes. By supercooling of the hexyl and heptyl derivatives a new liquid crystalline phase can be obtained. A dielectric relaxation in the solid phase could not be found.     

Computer Simulation of Biphenyl-Phenyl Ester Liquid Crystals

Abstract

Molecular orbital (MO) calculation and molecular dynamics (MD) simulation were carried out for a set of smectic liquid crystalline molecules, 8O-O8 (4-octyloxyphenyl-4′-octyloxybi-phenyl-4-carboxylate) and 8O-8 (4-octylphenyl-4′-octyloxybiphenyl-4-carboxylate), to understand the molecular origin of different crystalline structure formation and to predict their conformational property in liquid crystalline phases. The results of MO and MD analyses indicate that the structure of 8O-O8 and 8O-8 in crystalline phase is essentially determined by intramolecular interactions and the experimentally observed structure is chosen as a consequence of intermolecular packing constraints. This paper also reports the first application of two-molecular ab-initio calculation to liquid crystalline systems.     

Formation of ordered nanostructures in liquid-crystalline block copolymers with side-chain semiconductor materials

ABSTRACT

We developed a novel block copolymer composed of poly(ethylene oxide) (PEO) and polymethacrylate functionalized with liquid–cryst-alline oligothiophene by using the atom transfer radical polymerization (ATRP), aiming at application to organic photovoltaic (OPV) cells. Thermal investigation showed that the resultant polymer exhibits liquid–crystalline phases both on heating and cooling. Morphologies of the thin films of the block copolymer were investigated by atomic force microscopy (AFM). Microphase separation with a small size of almost 10 nm (nano-phase-separated structures) was observed upon annealing.     

Highly Conducting Derivatives Of Polyacetylene And Poly-Pyrrole Formed In The Reaction With Selected Protonic Acids And Metal Halides - Synthesis And Application

Abstract

It has been found that polyacetylene can be used in chemical analysis for selective determination of nitrate ion in dilute aqueous solutions. If such solutions are acidified with sulphuric acid the log σ vs. NO₃ concentration plots are linear over the NO^? ₃ concentration range 2–40 mM. Several new conducting derivatives of chemically polymerized polypyrrole have been prepared in the reaction with selected metal halides such as: FeCl₃, SbC1₅, and others. The products have been characterized by elemental analysis and conductivity measurements.     

C high-resolution NMR study of the effect of the deuterium isotope on liquid crystal CBOOA-d17

High-resolution ¹³C NMR experiments were performed in isotropic liquid and liquid crystalline phases of 4-octyloxy-N-(4-cyanobenzylidene)aniline (CBOOA) and its chain-deuterated analogue (CBOOA-d₁₇). The spin-lattice relaxation times (T₁) for each carbon atom in the molecules were measured to elucidate the differences between molecular interactions in CBOOA and CBOOA-d₁₇.     

MOLECULAR AND COLLECTIVE PROCESSES IN THE ANTIFERROELECTRIC PHASE OF A CHLORINATED COMPOUND

Abstract

New liquid crystalline substance, (S) 4-(1-methylheptyloxycarbonyl)-3-chlorophenyl 4′-(4-butanoiloxybut-1-oxy)biphenyl-4-carboxylate, exhibiting ferroelectric and antiferroelectric phases have been studied by means of frequency domain dielectric spectroscopy. DSC calorimetric and electrooptic measurements were done to study its phase transitions and electrooptic behaviour. In the antiferroelectric SmC_A* phase one of the dielectric relaxation modes exhibits a non-Arrhenius behaviour. The plots of critical frequencies and dielectric increments vs. temperature show an anomalous behaviour of the relaxation processes in the neighbourhood of the ferroelectric — antiferroelectric phase transition. Reversal current method reveals one current peak in the ferroelectric phase and two in the antiferroelectric one. Temperature dependencies of tilt angle, spontaneous polarization, switching time and transmittance are also presented and discussed in scope of the mean-field theory.     

Synthesis and Characterization of Polyphenothiazene Iodine Complexes

Abstract

N-methyl 3,6 dibromophenothiazene has been polymerized by using a nickel complex-assisted Grignard coupling. Vapor phase iodine doping of the organometallic polymerized material led to a conductivity increase of 10^?11 ohm^?1 cm^?1 to 10^?5 ohm cm^?l at room temperature. The complex thus formed exhibited a semiconductor behavior with a thermal activation energy of 0.1 eV and a strong electronic IR absorbance from 4000–400 cm^?1. However, the complexed polymer could be dissolved in liquid I₂ and cast into films with air stable, room temperature conductivities as high as 1 ohm^?l cm^?l. The mechanisms that could give rise to these differences in behavior will be discussed.     

Bilayered Super-Structures of Antiferroelectric Mesogens

Abstract

Crystal structures of two antiferroelectric mesogens, TFMHPBC and MHPBC-10, were analysed by an X-ray diffraction method. In both crystals, mesogen molecules formed a herringbone structure which was essentially the same as that proposed for the antiferroelectric liquid crystal phase. Because of the crystallographic 2₁-symmetry along the b-axis, only the b-axis component of the dipole moment remains in a smectic layer. Since the dipole moment in the next layer has the same magnitude but the opposite direction, both crystals show no dipole moment as a whole. These structural features observed in their crystal states seem to be conserved in their antiferroelectric liquid crystal phases which are just above their crystal phases.     

Mesogenic Properties of 5-Cyanotropolone and 2-Amino-5-Cyanotropone Derivatives

Abstract

New 5-cyanotroponoid liquid crystals with a 3,4-dialkoxybenzoyloxy and a 3,4-dialkoxybenzoylamino substituent at the C-2 position were prepared. These derivatives exhibited interdigitated bilayer smectic A phases while the corresponding benzenoids were non-mesogenic. Thermal stabilities of these troponoids were lower than those of 2-(4-alkoxybenzoyloxy)-5-cyanotropones and 2-(4-alkoxybenzoylamino)-5-cyanotropones.     

Calorimetric investigations of 2-[4-n-alkylphenyl]-5-[4-n-alkyloxyphenyl]-pyrimidines

We investigated temperatures and enthalpies of the phase transitions by means of the calorimeter DSC-2. The kinetics of polymorphic transitions in the solid state, the pretransitional behaviour in the liquid crystalline phases and the transition enthalpies, ranging from 3 J/mol up to 50 kJ/mol, in relation to the occurrence of the liquid crystalline phase types S_G, S_F, S_C, S_A, and N are points of discussion.     

Truxene Derivatives

Eight hexa-n-alkanoyloxy truxenes are presented. These new disc-like liquid crystals exhibit both columnar and N _D nematic phases. The N _D nematic phase is the first low temperature one. All these compounds show an inverted nematic-columnar sequence: the fluid N _D nematic phase is observed while heating after the crystalline phase below one or two viscous columnar phases and shows a phenomenon quite similar to the reentrant nematic behaviour.     

Studies on Anisotropic Molecular Orientation and Mesophase Stability in a Ternary Mixture of Liquid Crystalline Materials

The multicomponent system of cholesteryl linolenate (CL), sodium oleate (Naol), and orthophosphoric acid (H₃PO₄) exhibits liquid crystalline mesophases, like cholesteric and smectic phases, such as SmA, SmC, SmB, and SmG sequentially when the specimen is cooled from its isotropic phase. These phases have been observed by using microscopic technique. Helfrich potential and elastic moduli have also been estimated in the smectic phase using Helfrich model. Optical transmittance and electrical conductivity have also been discussed.     

Hysteresis at the Lα–Pαβ Phase Transition in Hen Egg Lecithin

Infrared spectroscopy in the OH and CH stretching region of very thin samples of hydrated egg yolk lecithin reveals an hysteresis at the transition between the two liquid crystalline phases L_α (higher temperature phase) and P_αβ . Both of these phases havea lamellar structure with alternating hydrophilic and hydrophobic layers, but they differ as to the state of the interiors of the layers. The hysteresis can be explained in terms of a coupling between the structures and the dynamics of adjacent layers.     

From Chiral Molecules to Chiral Liquid Crystal Phases

Abstract

During the last decade, the topic of chirality and symmetry in physical sciences has become extremely important, particularly as nature itself is often described as being “handed” or chiral. In liquid crystalline systems many important properties are known to be related to chirality, for instance chirality is reflected in helical structures, in special cases of strongly twisted systems novel frustrated phases may appear such as Blue phases and Twist Grain Boundary phases. In addition, many modern high technology applications, such as ferroelectric displays depend entirely on the presence of chirality in the liquid-crystalline materialsemployed.     

Synthesis of novel azoester homologous series of liquid crystalline behavior and the study of mesomorphism dependence on lateral substitution of middle phenyl ring

The titled azoester liquid crystalline homologous series consists of eleven homologues. The pentyl to tetradecyl derivatives of the series are nematogenic without exhibition of smectogenic character. Rest of the members of the series are nonliquid crystalline in nature. Textures of the nematic mesophase are schlieren or threaded type. Transition curves in the phase diagram showed normal phase behavior. Transition temperatures and liquid crystal behavior observed under an optical polarizing microscope equipped with a heating stage. An odd even effect is observed for nematic-isotropic transition curve. Analytical and spectral data confirms the structures of the molecules. Present homologous series is predominant nematogenic and partly nonmesogenic. Average thermal stability for nematic is 125.33°C and nematogenic mesophase length varies between 12°C to 48°C at tetradecyl (C₁₄) and octyl (C₈) derivatives, respectively.     

Raman spectroscopic studies of aluminium fluoroberyllate glasses

Aluminium fluoroberyllate glasses obtained in the vitreous domain from the quaternary system BaF₂CaF₂AlF₃BeF₂ have been studied by Raman spectroscopy. The observed bands have been assigned by comparison with those of cryolite molten aluminofluorides, and of various fluoroberyllates in the crystalline and molten state. The following species have been identified: (AlF₄)^? tetrahedral groups, (AlF₆)^?3 octahedral groups polymerized in chains, and a few polymerized species of beryllium fluoride and probably Be₂F₇^?3 dimers.     

Synthesis,structure, and mesomorphism of novel liquid crystalline acrylate monomers and polymers

A series of novel liquid crystalline monomers (M₁?M₈) and side chain polymers base polyacrylate backbone were synthesized. The chemical structures were characterized by FT-IR and ¹H-NMR spectra. The mesomorphism and thermal behavior was investigated by polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis. The relationships of structure and mesomorphism are discussed in detail. The eight monomers and their corresponding polymers all show enantiotropic nematic phase. With increasing the spacer length or flexibility of the terminal group, the melting temperature (T_m) and isotropic temperature (T_i) of the corresponding monomers and polymers all decreased. However, with increasing the rigidity of the mesogenic core, T_m and T_i of the corresponding monomers and polymers all increased. TGA showed that all the polymers obtained in this study had excellent thermal stability.     

Observation of Four Crystalline Phases of the One Dimensional Conductor Zn0.81 [Pt(C2O4)2] . 6D2O by Neutron Diffraction

Four different crystalline phases of Zn_0.81[Pt(C₂O₄)₂].6D₂O have been observed and partially characterized by single crystal neutron diffraction measurements. A crystal in the previously reported orthorphombic α-form was pulled along its c-axis at room temperature and was found to transform to a monoclinic β-form. Two new coexisting phases, monoclinic γ-Zn-OP and orthorhombic δ-Zn-OP were found when the sample was cooled to 200 K. Further crystallographic work is necessary in order to establish the detailed nature of the new phases.     

Phase formation upon crystallization of SrO · 2B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The crystallization of SrO · 2B₂O₃ glasses has been studied. Four different crystalline formations were found to form simultaneously and independently on the glass surface: stable α-SrB₄O₇ crystals and metastable crystalline forms (β-SrB₄O₇, Sr₄B₁₄O₂₅, and spherulites (presumably, mixtures of crystalline phases)). The ranges of thermal stability of the newly formed metastable phases have been established using thermal analysis.