摘要:

Two binary mixtures of polar liquid crystal materials were previously reported to exhibit three incommensurate smectic A phases predicted for such materials on the basis of phenomenological theory. Results of our recent high-resolution X-ray scattering experiments show that no incommensurate phases exist in the two systems. Wide coexistence regions are found at first order transitions between various frustrated smectic phases of these mixtures. These regions were previously identified as the incommensurate smectic A phases. The phase diagrams of the two systems determined with high-resolution X-ray technique are shown to be in excellent agreement with Baroisa-Prost-Lubensky theory.

ISSN:0267-8292    

DOI:10.1080/02678299408029161

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The sysnthesis and characterization of two series of chiral mononuclear palladium(II) azocompounds, (LN(n))Pd(acac)], prepared by bridge splitting reactions or the dinuclear parents {Pd[LN(n)]μ-Cl)}2with thallium acetylacetonate are reported. All the complexes, bearing a stereogenic centre in the alkoxy lateral chain (R*O=R-(−)-2-octyl;S-(−)-β-citronellyl), are mesomorphic. Their thermotropic behaviour has been investigated by differential scanning calorimetry, optical microscopy and X-ray diffraction. Worthy of note, the clearing temperatures of all the compounds are below 70°C. The relationship between ligands, μ-Cl dimers and mononuclear acetylacetonate complexes is discussed.

ISSN:0267-8292    

DOI:10.1080/02678299408029162

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We have investigated the distribution of conformations and orientations for a simple internal rotor molecule, 2,2′-bithienyl dissolved in liquid crystal solvents, by re-analysing published proton dipolar coupling data with the maximum entropy internal order method (MEIO). We show that detailed, model independent, conformational information can be obtained when data of sufficiently high quality are available. We also propose a novel and convenient representation method for the orientational-conformational coupling.

ISSN:0267-8292    

DOI:10.1080/02678299408029163

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new smectic phase existing between SEand SBin the non-polar compound 4,4′-dipentylbiphenyl was observed (DPB). It has been termed smectic E′ [1]. Enthalpies and phase transition temperatures for DPB were measured and characteristic textures of all three smectic phases are presented.

ISSN:0267-8292    

DOI:10.1080/02678299408029164

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Thermotropic cholesteric liquid crystals made of mixtures of cholesteric esters and of a Δχ <0 nematic (ZLI2806) may be used as NMR solvents to visualize enantiomers. Proton decoupled deuterium NMR spectra of a racemic mixture show that the quality of the spectra strongly depends on the temperature and on the nature and the concentration of the ester. A relationship between the spectral resolution and the presence of textural defects in the mesophase is also discussed. The best results, both for spectral resolution and enantiomeric separation, were obtained with a 45/55 by weight mixture of cholesteryl butyrate and ZLI2806 at 368 K.

ISSN:0267-8292    

DOI:10.1080/02678299408029165

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new type of highly organized, large scale propagation of vortical flow has been observed in MBBA subject to a transverse electric field. This is a transient phenomenon associated with the transformation, occurring at elevated voltages, between electrically distorted homeotropic and planar states. The convective flows generate an array of linear defects which persist even after removal of the field.

ISSN:0267-8292    

DOI:10.1080/02678299408029166

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

New ‘side-on’ attached liquid crystal polysiloxanes have been synthesized with different fixation ratios of side groups and various degrees of polymerization. For these syntheses, a series of random copoly(hydrogenmethyl-dimethylsiloxane)s, used a precursors, has been realized. Both thermal properties and small angle neutron scattering experiments on these polymers show a dècrease in the nematic ‘jacketed’ effect as the number of mesogenic groups fixed to the backbone decreases and as the main chain length increases.

ISSN:0267-8292    

DOI:10.1080/02678299408029167

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This contribution is concerned with molecules composed of rigid linear segments which are connected in such a way that a λ-shape results. Such types of shape have been predicted to lead to an enhanced solubility in low molar mass solvents and in the melt state of flexible chain molecules. The theoretical treatment predicted additionally that such molecules should be able to form lyotropic and thermotropic liquid crystalline phases. Experimental data on the thermodynamic properties, the structure formation in the solid and fluid condensed state, the solubility in low molar mass solvents and selected optical and electro-optical properties are reported; these are in good agreement with the predictions.

ISSN:0267-8292    

DOI:10.1080/02678299408029168

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

4-[(S)-2-Methylbutoxycarbonyl]phenyl 4-[(4-n-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]benzoates have been prepared from the starting material 1-pentafluorophenyl-2-trimethylsilylacetylene. Polarizing microscope textural observation and DSC measurements of the phase transitions of these novel compounds showed that they were liquid crystals with chiral smectic C phase (S*C), smectic A(SA) and cholesteric (Ch) phases. The effects of the alkoxy chain length on the transition temperatures and enthalpies were also studied.

ISSN:0267-8292    

DOI:10.1080/02678299408029169

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Surfactants from either polyisobutylene or alkylsuccinic anhydrides derivatized with diethanolamine in a 1:1 molar ratio with hydrocarbon and polyisobutylene chains of similar length formed lamellar liquid crystalsin situand also with added water. The repeat distance between layers was determined using low angle X-ray diffraction (LAXD), and the water penetration into the hydrocarbon space in the lamellar structure was calculated.

ISSN:0267-8292    

DOI:10.1080/02678299408029170

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor