Dielectric investigations in the nematic and hexatic smectic B phases of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl

Temperature-dependent dielectric characterization of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl (HIEB), which exhibits smectic B and nematic phases, has been carried out over the frequency range of 1 Hz to 10 MHz for homeotropic and planar alignment of sample molecules. This compound shows positive dielectric anisotropy (Δε = ε _∥ ? ε _⊥ > 0) in the nematic (N) phase. One mode of dielectric relaxation showing Arrhenius behaviour has been detected in the hexatic smectic B (SmB) phase. Various electrical parameters, namely, dielectric anisotropy, relaxation frequency and activation energy, have been determined in the N and SmB phases.     

A radio-tracer study of self-diffusion in the smectic phases iso-butyl 4-(4′-phenylbenzylideneamino) cinnamate [IBPBAC]

Average translational self-diffusion coefficients, , have been determined in the smectic E, B and A phases of unaligned samples of iso-butyl 4-(4′-phenylbenzylideneamino) cinnamate. A radiotracer technique was employed which was based on the serial sectioning method used in the study of diffusion in solids. In the smectic E phase is about 1 × 10^-14 m² s^-1. The self-diffusion in the smectic B phase fits reasonably well to an Arrhenius law with an activation enthalpy of 82 kJ mol^-1. The transition from the smectic B to A phase results in a dramatic rise in . In the smectic A phase the results fit an activation enthalpy for self-diffusion of about 168 kJ mol^-1. Similarities between the diffusion in the smectic E and B phases and in plastic solids are observed.     

Representations of the nonstandard (twisted) deformationU′ q(so n ) forq a root of unity

Irreducible representations of the algebrasU′ _q(so _n ) forq a root of unityq ^p=1 are given. The main class of these representations act onp ^N-dimensional linear space (whereN is a number of positive roots of the Lie algebra so _n ) and are given byr = dim so _n complex parameters. Some classes of degenerate irreducible representations are also described. Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000. The research described in this publication was made possible in part by Grant UP1-2115 of the U.S. Civilian Research and Development Foundation for the Independent States of the Former Soviet Union (CRDF).     

Structure and biological properties of sodium and potassium 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionates

Sodium (1) and potassium (2) 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionates form crystal hydrates, which exist as both monomers and dimers. Quantum-chemical calculations in the PM6 approximation are used to determined the enthalpies of formation ?H _f ^po , thermal enthalpy H ^po, and entropy S ^po of the monomers and dimers, which are indicative of the possibility of existence of the dimers of propionates of alkali metals. The biological activity of these compounds in animal and plants is demonstrated to be dependent on their concentrations. Compounds 1 and 2 turned out to be efficient in the treatment of burn injuries, cancer, and radiation damage (in vivo and in vitro), as well as in promoting the growth of cereal plants.     

C-13 and H-1 NMR Study of Alkyl and Aryl-Substituted 1-(4′-Dimethylaminobenzylideneamino)pyridinium Perchlorates

C-13 and H-1 NMR spectra of some 1-(4′-dimethylaminobenzylideneamino)pyridinium perchlorates show that the angle of twist of the pyridine ring in unsubstituted, 1, and 2-alkyl substituted compounds 2–5 is comparable. However, it is considerably increased in 2,6-dialkyl derivatives. As seen from the spectral data, pyridine and phenyl rings in 2,6-diphenyl derivative 15 are not coplanar. The effect of 4-alkyl substituent is of hyperconjugative chacter. In general, the amount of the positive charge at C-4 in 2,6-dialkyl substituted salts is higher as compared to 2-monosubstituted compounds.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

The properties of ferroelectric compound (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(4-cyanoacetoxybut-1-oxy) biphenyl-4-carboxylate and its ability of an antiferroelectric phase induction in mixtures

Phase transitions and ferroelectric properties of (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(4-cyanoacetoxybut-1-oxy)biphenyl-4-carboxylate will be described in this article. This compound exhibits the synclinic smectic C* phase and it has the ability to induce an antiferroelectric phase in mixtures with the other ferroelectric compounds. New systems with induced antiferroelectric phase and their properties are presented.     

Synclinic and anticlinic properties of (R,S) 4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy)heptyl-1-oxy]benzoates

Four racemic mixtures were synthesized and characterized. Their mesomorphic properties, such as phase transitions temperatures and enthalpies, were measured by a polarizing optical microscope and differential scanning calorimetry. The influence of one racemic mixture on the properties of the OAFLC mixture W-1000 was studied. The results show a wide temperature range of the SmC_A* phase in this new mixture. The helical pitch was measured by spectrophotometry method. The electro-optical properties of the mixture were also presented and discussed.     

The characterization of electroplex generated from the interface between 2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole] zinc and N,N′-diphenyl-N,N′- bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine

The electroplex between (2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole) zinc [Zn(4-TfmBTZ)₂] as an electron-acceptor and N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) as an electron-donor was characterized by bilayer, blend, and multilayer quantum-well (MQW) device, respectively. The blend composition and quantum-well number are effective parameters for tuning electroluminescence color. White light with high color purity and color rendering index (CRI) was observed from these devices based on Zn(4-TfmBTZ)₂/NPB. Moreover, the blend and MQW devices all exhibit high operation stability, hence excellent color stability. For the device with 5 mol% NPB in blend layer, its Commission International Del’Eclairage (CIE) coordinate region is x=0.28–0.31, y=0.33–0.35 and CRI is 83.3–91.2 at 5–9 V. For MQW structure device with NPB of 60 nm thickness, its CIE coordinate region is x=0.29–0.32, y=0.31–0.34 and CRI=87.9–92.5 at 10–15 V. Such high color stability and purity and CRI, being close to ideal white light, are of current important for white OLED.     

Nuclear magnetic relaxation of nematic liquid crystals,N-(4-methoxybenzylidene)-4′-n-butylaniline and N-(2-hydroxy-4-methoxybenzylidene)-4′-n-butylaniline

Nuclear magnetic resonance linewidth and spin-lattice relaxation time T₁ were measured for 4-methoxybenzylidene-4′-n-butylaniline (MBBA) and N-(2-hydroxy-4-methoxybenzylidene)-4′-n-butylaniline )OHMBBA) in their liquid, nematic, undercooled nematic, and glassy nematic liquid crystal states as well as in the stable crystalline states. In the case of OHMBBA, the motional narrowing occurs in three steps corresponding to excitation of end-group reorientations, self-diffusion, and molecular tumbling. T₁ of OHMBBA in the nematic and undercooled nematic state has two minima at 264 K (24 ± 4 msec) and at 140 K (22.0 ± 0.5 msec); the motions responsible for the minima are the self-diffusion and the end-group reorientations with the activation energies 29 ± 1 J mole⁻¹ and 5.8 ± 0.2 kJ mole⁻¹ respectively. Analogous results were obtained for MBBA. Some measurements were also made for p-azoxyanisole for the sake of comparison. The effect of external magnetic field on the formation of the glassy state was examined.     

HREM analysis of structure and defects in a Σ5 (210) grain boundary in rutile

The structure of a 5 (210) boundary in rutile was investigated by high resolution electron microscopy (HREM). The boundary was stepped with an average inclination of about 5° from the symmetrical (210) plane. The steps were associated with 1/5[210] DSC lattice dislocations accommodating a deviation of about 2° from the exact 5 misorientation of 53.1°, and resulting in a misorientation of 51°. The boundary topography, the location of structural units and the local symmetry were determined using pattern recognition techniques. Flat terraces between steps had a periodic 5 (210) structure which exhibited mirror glide symmetry. Image simulations showed best agreement with experimental images for a model structure with a rigid body shift of 0.21 nm parallel, and a 0.10 nm volume contraction normal to the interface. This structure requires a high density of defects or an excess of Ti ions, presumably of lower oxidation state.     

Evolution of texture and grain boundary microstructure in two-phase (α + β) brass during recrystallization

The evolution of texture and microstructure during recrystallization is studied for two-phase copper alloy (Cu–40Zn) with a variation of the initial texture and microstructure (hot rolled and solution treated) as well as the mode of rolling (deformation path: uni-directional rolling and cross rolling). The results of bulk texture have been supported by micro-texture and microstructure studies carried out using electron back scatter diffraction (EBSD). The initial microstructural condition as well as the mode of rolling has been found to alter the recrystallization texture and microstructure. The uni-directionally rolled samples showed a strong Goss and BR {236}?385? component while a weaker texture similar to that of rolling evolved for the cross-rolled samples in the α phase on recrystallization. The recrystallization texture of the β phase was similar to that of the rolling texture with discontinuous ?101? α and {111} γ fiber with high intensity at {111}?101?. For a given microstructure, the cross-rolled samples showed a higher fraction of coincident site lattice Σ3 twin boundaries in the α phase. The higher fraction of Σ3 boundaries is explained on the basis of the higher propensity of growth accidents during annealing of the cross-rolled samples. The present investigation demonstrates that change in strain path, as introduced during cross-rolling, could be a viable tool for grain boundary engineering of low SFE fcc materials.     

Translational order parameter in the smectic-B phase of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl

4-Hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1-1′-biphenyl, a liquid crystalline material shows smectic-B (SmB) and nematic phases, respectively, between 60.3–98.5°C and 98.5–130.8°C. X-ray diffraction patterns were recorded at different temperatures in the SmB phase and were used to compute translational order parameters. For this purpose, we have employed a theoretical model recently reported by Kapernaum and Giesselmann. The results obtained are discussed in terms of the basic understanding of the SmB phase.     

The decays of theρ′1 andω′1 mesons

New measurements of the reactione ⁺ e ^– confirm previous evidence for the decay₁ and provide a strong constraint on the mass of the₁. The results from a detailed analysis of these data are compared with those from a corresponding analysis of new data on the reactione ⁺ e ^–. It is shown that in accord with expectation. This identification of a strong₁ decay supports a previous claim that the₁ and theC(1480), observed in the channel, cannot be different manifestations of the same particle.     

Distribution of doped Mn at the Σ3 (1 1 2) grain boundary in Ge

Using first-principles density functional theory method, we have investigated the distribution and magnetism of doped Mn atoms in the vicinity of the Σ3 (1 1 2) grain boundary in Ge. We find that at low concentration, the substitutional sites are energetically favorable over the interstitial ones for Mn. The binding energy of Mn varies with lattice sites in the boundary region, and hence a non-uniform distribution of Mn nears the boundary. However, the average of their segregation energy is quite small, thus no remarkable grain boundary segregation of Mn is predicted. Due to volume expansion at the grain boundary, the spin polarization of Mn is slightly enhanced. Overall, we find that the magnetism of Mn-doped Ge is not sensitively dependent on the grain structure.     

Chirality and the thermophysical properties of molecular solid phases under pressure: (+)- and (±)-camphor

Thermal conductivity λ, heat capacity per unit volume pc_P and P-T phase diagrams are investigated for both (+)- and (±)-camphor. The transient hotwire method is used at temperatures in the range 100–430 K and at pressures up to 1·75 GPa. We detect solid phases I-IV for (+)-camphor and I′-V′ for (±)-camphor. We conclude that λ is independent of enantiomeric composition for plastic-crystal phase pairs I-I′, II-II′ and IV-IV′. Phase V′ also appears to be a plastic-crystal phase. Non-plastic phases III and III′ show a variation of λ with T that differ considerably from that expected for a simple crystal, with the greatest such difference being observed for the racemic compound III′. An unannealed specimen of the racemic compound III′ is probably chirally disordered and shows a variation of λ with T for T < 130 K, which may indicate phonon-assisted fracton hopping.