ISSN:0267-8292    

DOI:10.1080/02678298608086485

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This article describes the progress in experimental studies of liquid-crystalline blue phases during the past 5 years. Additionally, these results are compared critically with the predictions of theories of the blue phases. Areas considered in this review include (i) the thermodynamic stability of the three polymorphic blue phases and the influence of the cholesteric pitch on this; (ii) the phase diagrams of blue phases; (iii) electric field effects on the blue phase structure and stability; (iv) the morphology and growth of liquid single crystals of blue phases; (v) the symmetry and structural properties of the blue phases.

ISSN:0267-8292    

DOI:10.1080/02678298608086486

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The values of twisting power of a chiral bridged binaphthyl and (+)-trans-stilbene oxide in a rigid hydrocarbon perhydrophenanthrene nematic are much smaller than in conformationally flexible nematics, indicating the importance of the solvent structure for cholesteric induction. The perhydrophenanthrene phase constitutes an excellent solvent for linear dichroism measurements of anthracene but it is unable to orient 9,9′-spirobifluorene.

ISSN:0267-8292    

DOI:10.1080/02678298608086487

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The nematic substance 5CB is known from N.M.R. studies to be slightly biaxial, not in the sense that any bulk property measured in a direction at right angles to the director is liable to vary with rotation about the director, but in the sense that there are biaxial terms in the ordering matrix that describes the alignment of individual molecules; (Sxx-Syy) is non-zero as well asSzz. We show that the biaxial terms should make a significant contribution to the magnetic anisotropy Δχ(m)of 5CB, and that the magnitude and temperature dependence of this bulk property, which we have measured, can be understood if, and only if, they are taken into account. The contribution which they make to the optical birefringence term ∑ should, however, be relatively trivial. Although ∑ may in principle be affected by local field corrections of a complicated nature, which do not affect Δχ(m), a new theory presented in an Appendix to the paper suggests that these too are likely to be relatively trivial. Hence we believe that ∑ is more nearly proportional than is Δχ(m)to the principal order parameterSzz.

ISSN:0267-8292    

DOI:10.1080/02678298608086488

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Time-resolved polarized fluorescence spectroscopy has for the first time, been applied to the study of chromophores in a macroscopically aligned lyotropic nematic phase. The phase is composed of potassium dodecanoate, potassium chloride and water and contains long rod-like aggregates, that are aligned with their long axes parallel to an applied magnetic field. Pyrene, 1-pyrene dodecanoic acid, 1-dodecylpyrene and l-palmitoyl-2-(6-pyrenylhexanoyl)-sn-glycero-3-phosphoryl-choline are solubilized in these aggregates. The photophysics of these probes is a single exponential and typically between 130 and 200 ns in non-degassed samples. For all the probes the plane of the pyrene molecule tends to be oriented perpendicular to the symmetry axis (C∞axis) of the aggregate. The order parameters describing the orientation of the electronic transition dipole moment relative to this axis are typicallyc.-0.05. It is concluded that the translational and the local rotational motions of the probes are fast compared to the fluorescence lifetimes. The correlation times characterizing these motions are shorter than 20 ns. Finally, no slow motions such as fluctuations of the normal to the surface of the rod-like aggregate or a slow wobbling of theC∞-axis can be detected duringc.1 μmls.

ISSN:0267-8292    

DOI:10.1080/02678298608086489

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The optical microscopic mass transport (OMMT) method was utilized to determine the cholesteric pitch values of the mixtures of mesogenic and non-mesogenic chiral species in nematic materials. The cholesteric pitch was determined by transient analysis of the diffusion profile established by allowing an initial cholestric composition (solute) to diffuse under semi-infinite linear boundary conditions into an oriented thin film of its corresponding nematic solvent. During the steady-state diffusion, where the initial concentration (pitch) remains constant, the transient analysis of the profile with a polarization microscope exhibits a maximum number of pitch discontinuity domains. The evaluation of the unknown pitch was carried out by extrapolation of the diffusion pitch gradient to the original diffusion source by using the exact relation between the pitch and the film thickness. The method is experimentally simple; at constant temperature and pressure, determination of the pitch depends only on the film thickness. There is a good agreement between the pitch values obtained with this method and those from conventional techniques.

ISSN:0267-8292    

DOI:10.1080/02678298608086490

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The lyotropic mesophases of alkali metal salts of 4-trans-pentyl cyclohexanoic acid have been studied. The lithium salt is of particular interest in that it forms a lyotropic nematic phase, a hexagonal phase, and another columnar phase, possibly with a rectangular lattice. Unlike most nematics, this phase can assume a parallel alignment on a treated surface in much the same way as thermotropic (molecular) nematics. When the nematic dries, a columnar phase grows into it, showing a strong preferential direction of the column axes. This system should be useful in studying the nematic-columnar transition and in other investigations which require an aligned micellar nematic phase.

ISSN:0267-8292    

DOI:10.1080/02678298608086491

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A high resolution a.c. calorimetric study has been carried out on a mixture of 4-n-hexylphenyl-4′-(4″-cyanobenzoyloxy)benzoate (DB6) and terephthalylidene-bis-(4-n-butylaniline) (TBBA). The heat capacity at the smectic A1—smectic A2(SA1-SA2) transition in a DB6+ 15 per cent TBBA mixture exhibits a distinct cusp with a critical exponent α ⋍ -0.15. This value for a is consistent with the critical correlation exponent v obtained from X-ray scattering, but it does not conform with current theoretical predictions that the SA1-SA2transition should belong to the Ising universality class.

ISSN:0267-8292    

DOI:10.1080/02678298608086492

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The mechanism of thermally- and solvent-induced cholesteric sense inversions in lyotropic polypeptide liquid crystals has been discussed based on deuterium N.M.R. observations for poly(γ-benzyl L-glutamate) with perdeuteriated sidechain benzyl ester groups. Comparison of the deuterium quadrupolar splitting pattern with the macroscopic helical twisting power indicates that the sense inversion does not necessarily require sidechain conformational transitions (or changes in the helix surface chirality). The new data support a less specific mechanism for sense determination in polypeptide liquid crystals: anisotropic intermolecular interactions between helices are influenced by the solvent dielectric medium.

ISSN:0267-8292    

DOI:10.1080/02678298608086493

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

For a nematic solution of polydisperse rigid rods the osmotic pressure is proved to be independent of the length distribution and proportional simply to the total number density. This rule holds in the gaussian approximation to the Onsager theory. Its accuracy is demonstrated for bidisperse systems.

ISSN:0267-8292    

DOI:10.1080/02678298608086494

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor