摘要:

A new methodology has been employed in synthesis of two side-chain liquid-crystalline polymers with cyanobiphenylene mesogenic groups and variation of -CN, -COCH3and -OH groups displacement in the backbone surrounding. Hydrodynamic and electrooptical (the Kerr effect) methods were used to study their molecular properties in solution in benzene and chloroform. Electrooptical properties of polymers are compared with the same ones of homologous series of alkoxycyanobiphenylenes as the model compounds of the polymer mesogenic groups. Different mobility of the side-chain mesogenic groups in polymers under investigation was observed and related to the chemical and dipole structure.

ISSN:1058-725X    

DOI:10.1080/10587250008024425

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Phase transition of liquid crystal carboxylate from crystalline state (K) to smectic phase B (SB) is investigated by low-frequency internal friction (IF) and DSC method. The IF peak temperature increases with the increase of heating rate, but it has no clear dependence on vibration frequency. The experimental results agree with the characters of the low-frequency IF associated with first-order phase transition, and the change in the quantity of phase interface is responsible for the IF peak.

ISSN:1058-725X    

DOI:10.1080/10587250008024426

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Chemiluminescence during free radical oxidation of cholesteryl esters has been studied in isotropic and cholesteric liquid crystalline phases. A dramatic enhancement of the chemiluminescent intensity was observed in the cholesteric phase. The emitter of chemiluminescence in this reaction is an electron excited ketone that forms during recombination of cholesteryl ester peroxyl radicals. It was shown that an enhancement of the intensity is due to an increase in both quantum yield of the excited state and emission yield of the emitter as the phase order increases. These phenomena are attributed to interplay between the orientational order of the medium and the anisometry of the reacting species. An increase in quantum yield of the excited state of the emitter is explained in terms of the increased rigidity of the transient tetraoxide complex during recombination of peroxyl radicals of cholesteryl esters in an anisotropic environment.

ISSN:1058-725X    

DOI:10.1080/10587250008024427

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Phenanthro[b]phenazine, a new heterocyclic ring structure of both biological and physical interests, has been prepared by coupling 1, 2-phenylenediamine with triphenylene-2, 3-quinone derivative. The first derivative of this novel core, 2,3,6,7-tetrapentyloxyphenanthro[b]phenazine, shows a monotropic columnar phase.

ISSN:1058-725X    

DOI:10.1080/10587250008024428

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The conformational properties of binaphthol (BN) derivatives dissolved in a pentylcyanobiphenyl liquid crystalline (LC) matrix were determined by molecular dynamics (MD) simulation. Due to the influence of intermolecular interactions between the molecules of the LC matrix and the BN molecules, the conformations of the BN molecules in LC phase are found to change in the direction from transoid to cisoid on heating that results in decrease of observed helical twisting power (HTP). The changes of molecular conformation are mainly connected with orienting potential acting on solute molecule.

ISSN:1058-725X    

DOI:10.1080/10587250008024429

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper presents the equations of capillary hydrostatics for interfaces between viscous isotropic fluids and nematic liquid crystals. The interfacial stress balance equation involves the surface divergence of the surface stress tensor. It is shown that the anisotropic elastic contribution due to weak anchoring give rise to bending stresses not observed in isotropic fluids. It is shown that surface gradients of the bending stresses are a source of interfacial normal forces even in planar interfaces. Surface gradients in the normal surface stresses due to weak anchoring generate interfacial tangential forces, equivalent to those present in the thermocapillarity, electrocapillarity, and diffusocapillarity of isotropic fluids. Mathematical expressions corresponding to biaxial nematics for anisotropic surface elasticity, surface stress tensor, Marangoni and normal forces are derived, characterized, and used to establish the main interfacial phenomena driven by nematic biaxial ordering.

ISSN:1058-725X    

DOI:10.1080/10587250008024430

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The interaction of two ubiquinones having different chain lengths, ubiquinone-2 and ubiquinone-10 with 2 saturated or 10 unsaturated isoprenoid groups, with dipalmitoylphosphatidylcholine (DPPC) has been studied in mixed monolayers. The miscibility of the mixtures has been investigated by pressure-area measurements and simultaneous fluorescence microscopy at the air-water interface. Results were analyzed in terms of the additivity rule and the excess free energies of mixing were calculated from the compression isotherms in the full range of ubiquinone concentrations. We have also evaluated the area contribution of each ubiquinone molecule to the total molecular area of the mixed films. Stable monolayers are formed by the oxidized forms of the two ubiquinones but by increasing the lateral pressure, the ubiquinones are expelled from the films. The difference observed between the two ubiquinones in mixed monolayers are explained by a difference of localization according to their side chain lengths.

ISSN:1058-725X    

DOI:10.1080/10587250008024431

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Elastic waves in theo-terphenyl single crystal belonging to the orthorhombic system were measured by the Brillouin light-scattering spectroscopy. Wave vectors of elastic waves were obtained from three principal values of dielectric tensor determined by a new simple method. All nine elastic constants representing elastic contribution to the free energy have been determined, which show intermediate anisotropy between benzene and linear polyphenyls. The anisotropy can reasonably be explained from the arrangement of the phenyl bonds and the inter-molecular interactions caused from the packing of molecules in the crystalline lattice. It has been found that pure transverse elastic waves would not be observed in this system by the Brillouin scattering.

ISSN:1058-725X    

DOI:10.1080/10587250008024432

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The spatial polarisation distribution in inhomogeneously polar molecular crystals has been imaged by scanning pyroelectric tomography and simulated by a Markov process. The experimental technique combines scanning pyroelectric microscopy (SPEM) with layerwise thinning of crystals. The SPEM probes the local spontaneous polarisation by its temperature dependence (pyroelectric effect). A focused and intensity modulated laser beam scans the surface of a polar sample and induces temperature changes in a volume depending on the laser spot size and the thermal diffusion length λth. Since high lateral resolution of the SPEM is only available for small values of λth. depth information to a resolution of ∼ 10 μ is achieved by repeated scanning and stepwise thinning of crystals. A layer by layer technique can provide 3D imaging of the polar ordering with a lateral resolution of ∼ 20 μ at a probed layer thickness of ∼ 10 μ. Applied to perhydrotriphenylene (PHTP) co-crystallised with 1–(4-nitrophenyl)piperazine (NPP) two conical macro-domains of opposite and nearly constant polarisation were found. The SPEM results are in good agreement with a homogeneous Markov chain model driving dipolar molecules into a parallel state within channels of PHTP. The new tomographic view reveals that the opposing cones are partially overlapping at the tips. Lateral growth processes are assumed to be responsible for this. A theoretical section covers aspects of the convergency into the polar state and the length of polar chains discussed in terms of intermolecular interaction energies.

ISSN:1058-725X    

DOI:10.1080/10587250008024433

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Our recent studies have shown that simple alkyl chains can be used as crystal design elements to drive the formation of noncentrosymmetric lattices of interest in quadratic nonlinear optical applications. In a series of alkyl substituted diaminodicyanoquinodimethanes second harmonic generation was observed only in the systems with intermediate chain length. The molecular and crystal structures of 7,7–bis(n-pentylamino)-8,8-dicyanoquinodimethane, one of the SHG active crystals in this series, are presented in this paper. Dipolar, H-bonding and alkyl chain interactions are observed between the molecules in the crystal. Semiempirical quantum chemical computations on the molecule and detailed analysis of the experimental molecular and crystal structures reveal the critical role played by alkyl chain interactions in the formation of the noncentric lattice and the resultant SHG capability of this material.

ISSN:1058-725X    

DOI:10.1080/10587250008024434

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor