摘要:

It has been shown that the lyotropic liquid-crystalline phases formed by certain dyes are structurally analogous to the chromonic N and M liquid-crystalline phases previously thought to be unique to certain anti-asthmatic/anti-allergic drugs. We suspect that these two groups of compounds will prove to be representatives of a large new class of mesogenic materials.

ISSN:0267-8292    

DOI:10.1080/02678298608086274

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A novel, solid physical form has been observed when some water-soluble, reactive dyes are isolated from aqueous solution, as sodium salts, by the addition of sodium chloride. This quasi-crystalline form has a fibrous morphology, is birefringent but is not crystalline. Dyes of this type are known to form lyotropic liquid-crystalline mesophases in water. Preliminary X-ray diffraction investigations, reported here, for the mesophases formed by two such dyes indicate that they have columnar structures of the type first proposed for the lyotropic mesophases of the disodium chromglycate/water system and subsequently for other drug and dye molecules. X-ray and electron diffraction studies of the quasi-crystalline form show that it has a closely related columnar structure. The quasi-crystalline form is postulated to result from the formation and subsequent precipitation of columnar dye aggregates, as sodium chloride is added to the aqueous dye solution.

ISSN:0267-8292    

DOI:10.1080/02678298608086275

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The chirality of the constituent molecules in the chiral smectic phase induces a helical structure with a pitch,p0. Because of the tilt and chirality there is a spontaneous polarization and a bend deformation which act upon the induced helix. The resulting pitch is described as a function ofp0using the phenomenological theory of a chiral smectic C phase. The pitch,p0, is then calculated using a molecular theory of the cholesteric phase. The results obtained explain the experimental observations, at least qualitatively.

ISSN:0267-8292    

DOI:10.1080/02678298608086276

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Far infrared spectra in the frequency range 20 to 200 cm−1for the 4,4δ-di-n-alkoxyazoxybenzene homologous series are presented for the isotropic and nematic phases and for 0.1 M solution in benzene. In addition some partially deuteriated samples were studied. The spectra consist generally of two broad bands. By comparison of the spectra for different deuteriated compounds it is possible to interpret the higher frequency band as being connected with the intramolecular torsional vibration of the end groups. The band at lower frequencies we associate with the Poley absorption of librating molecules. The confined rotator model calculations performed for this band, for all compounds studied, give the rotational correlation time which is in good agreement with the correlation times as derived from quasi-elastic neutron scattering experiments.

ISSN:0267-8292    

DOI:10.1080/02678298608086277

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We report the solution of the excluded volume problem for a pair of biaxial hard molecules; namely, sphero-platelets. As an application of this result we study the isotropic to nematic liquid crystal transition for a fluid composed of these particles in the Onsager limit (length δ breadth or width). We show that the range of stability of the isotropic phase decreases with increasing particle biaxiality.

ISSN:0267-8292    

DOI:10.1080/02678298608086278

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Analytical expressions for the elastic constants of nematic polymer solutions are derived when the macromolecules are monodisperse rod-like, bidisperse rodlike or semi-flexible. These expressions are derived in the gaussian approximation so that they constitute exact leading terms of a general asymptotic expansion for high degree of nematic ordering although the results are justifiable only within the range of validity of the second virial approximation. The limiting forms are in complete agreement with recent numerical work for monodisperse rods.

ISSN:0267-8292    

DOI:10.1080/02678298608086279

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Results of dielectric relaxation, quasielastic neutron scattering, calorimetric D.S.C. and preliminary X-ray measurements on the fifth member, POAOB, of the 4,4'-di-n-alkoxyazoxybenzene homologous series are presented. It has been found that POAOB exhibits two mesophases: a nematic (N) and an intermediate crystalline phase (CI) just below it. From comparison of the dielectric relaxation and quasielastic neutron scattering studies we can conclude that in the nematic phase the molecule as a whole performs rotational diffusion around the long axis (ω ˜ 150ps) and at the same time the two moieties perform faster independent reorientations around the N-δ bonds (ω denotes a benzene ring) with δ ˜ 5 ps. The intermediate crystal phase is identified as a solid uniaxial rotational phase in which fast molecular reorientations exist. It seems that the fast reorientations observed in the nematic phase to some extent survive to the crystal I phase. A model of molecular arrangements in the crystal I phase is proposed, and it explains the reduction of the dielectric increment observed on passing from the nematic phase to this phase.

ISSN:0267-8292    

DOI:10.1080/02678298608086280

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A method for the measurement of the rotational viscosity, γ1of nematic liquid crystals under high pressure is described. First measurements for the liquid crystals 4'-methoxybenzylidene-4-n-butylaniline, a broad range nematic mixture of substituted cyclohexyl-phenyls and a re-entrant nematic mixture are presented.

ISSN:0267-8292    

DOI:10.1080/02678298608086281

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Four series of 4-alkoxyphenyl 4'-(4'-cyano- or nitro-benzoyloxy)-2'- or -3'-fluorobenzoates have been synthesized and the corresponding mesophases identified. These series show a rich variety of smectic modifications including several kinds of smectic C phases. A comparison of these series with related strongly polar mesogens is given.

ISSN:0267-8292    

DOI:10.1080/02678298608086282

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

First experiments show that cross-linked liquid-crystalline polymers, which are swollen with nematic low molar mass liquid crystals and freely dispersed in this liquid crystal, change their shape if an electic field is applied. This shape variation depends on the degree of swelling.

ISSN:0267-8292    

DOI:10.1080/02678298608086283

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor