摘要:

The weakly mesomorphictrans-4-alkyloxy-4′-stilbazoles(n-OPhVPy) are readily synthesised from alkyloxyiodobenzenes and 4-vinylpyridine in a palladium-catalysed Heck reaction. While the highly symmetric palladium and platinum complexestrans-[MCl2(n-OPhVPy)2] show mesophases only at very high temperatures, the lower symmetry platinum complexestrans-[PtCl2(η2-olefin) (n-OPhVPy)] melt below 100°C. Similarly, the complexes [MCl(CO)2(n-OPhVPy)] (M = Rh, Ir) are low melting. The silver complexes [Ag(n-OPhVPy)2][X] (X = C12H25OSO3, C8H17OSO3, CF3SO3) can be obtained by direct reaction of the stilbazole with AgX. These ionic materials show a rich thermotropic polymorphism, including nematic and cubic mesophases. Some fluorinated stilbazoles have also been synthesised and complexed to silver; the mesomorphism of these complexes is also reported.

ISSN:1058-725X    

DOI:10.1080/10587259208038507

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The paper describes methods for obtaining mixtures with a broad range of the smectic C phase and with the smectic A phase above the smectic C phase. It was demonstrated that doping is a very useful method for modification of the smectic C mixtures and for adjusting the tilt angle. It was also shown that smectic C mixture may be composed of compounds having no smectic C phase and that the concentration of these compounds can be large.

ISSN:1058-725X    

DOI:10.1080/10587259208038508

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

During the last five years a lot of new metallo-organic mesogens have been synthesized. The molecular architecture is more or less modified by the metallic atom and therefore the molecular organization in the columnar, smectic or nematic mesophases containing metals is specific of this new kind of mesogens. We present a comparative study of various series of metallo-organic complexes. In these complexes one (or two) metallic atoms link two (or more) identical mesogenic ligands; the structural features of the mesophases depend on the nature of the metal bridge, and of the length and the nature of the ligand. It is also possible to compare, in their respective mesophases, the organization of the complex to that of ligand alone. The global molecular shape is derived from usual X-ray diffraction experiments. Taking into account some features of the diffraction pattern related to the metal atoms ordering, it is possible to describe the molecular environment. The short-range ordering depends of the nature of the complex. Moreover, there are specific methods of investigation of the metal environment: the comparison of variable wavelength X-ray scattering experiments and neutron scattering experiments might give access to the metal-metal pairs correlation function. At last, by X-ray spectroscopic methods (EXAFS and XANES), it is possible to investigate the close neighbouring of the metallic atom.

ISSN:1058-725X    

DOI:10.1080/10587259208038509

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In aqueous solution, pure DNA forms multiple liquid crystalline phases when the polymer concentration is increased. A structural analysis of the different phases and of their transitions is presented here in polarizing and in electron microscopy. The cholesteric phase presents usually periodic patterns with series of nested arches in electron microscopy. The defects of the structure can be analyzed with the resolution of the electron microscopy and compared to the data available in polarizing microscopy. We show how the germs of the more concentrated phase nucleate preferentially along some types of defects of the cholesteric phase. The concentrated phasg is columnar hexagonal and behaves as a lamellar structure. Each layer (25 to 40 Å thick) is composed of DNA molecules aligned in parallel. Numerous screw dislocations, either left or right-handed, can be seen in the structure. Besides, the evolution of the hexagonal textures, induced by a progressive dehydration of the preparation, can be followed with the resolution of the electron microscopy. Finally, the biological interest of the liquid crystalline structure of DNA is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259208038510

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Recent advances in the development of ferroelectric liquid crystal displays are briefly reviewed, with special attention to the problems and solutions concerning cell bistability, matrix addressing techniques, the realization of gradation displays and the system integration of FLC displays. New dynamic models for matrix addressing are introduced.

ISSN:1058-725X    

DOI:10.1080/10587259208038511

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effects of distributions of dislocations, disclinations and charge admixtures on the structural transformations in thin LC films are discussed in the framework of the phenomenological approach. The quasiequilibrium spatial modulation of polarization in the ferroelectric LC after or under the external field actions is described as the result of modulated distributions of free charges and disclinations. The electrostatically induced growth of spiral domains in Langmuir monolayers at the air-water interface is described as the result of modulated distributions of the tilt angle and free charges in the chiral polarized thin film. The chiral smectic A* phase is described as the periodic distribution of dislocation walls and disclination loops in the layered system.

ISSN:1058-725X    

DOI:10.1080/10587259208038512

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

On the basis of data in literature and those obtained from our experiments we have analysed the influence of metal in the structure of rod-like and discoid amphiphilic molecules on their lyotropic mesomorphism.

ISSN:1058-725X    

DOI:10.1080/10587259208038513

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The isotropic ‐ nematic biphasic segregation has been investigated in a thermotropic main chain polyester by differential scanning calorimetry analysis. The width of biphasic gap has been determined and related to the molecular parameters of the polymer.

ISSN:1058-725X    

DOI:10.1080/10587259208038514

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Mechano-electric responses of artificial guest-host membrane systems (liquid crystal lipid matrix containing ion channels) and native biomembranes from locust muscle to stretch and curvature deformation of the matrix were studied. Gating of ion channels by lateral tension and enhancement of the flexo-electric response during channel openings were observed.

ISSN:1058-725X    

DOI:10.1080/10587259208038515

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A number of new disc-like pentaynes1–4with super-disc cores are presented. These new non-mesogenic electron donors doped with 2,4,7-trinitrofluorenone(5)form charge transfer complexes showing enantiotropic nematic and hexagonal columnar mesophases.

ISSN:1058-725X    

DOI:10.1080/10587259208038516

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor