摘要:

The so-called ‘smectic’ D phase of 4′-n-octadecyloxy-3′-cyanobiphenyl-4-carboxylic acid (one of only four materials known to exhibit this phase) has been shown unambiguously by X-ray diffraction to be characterized by a primitive cubic space group. The space group is eitherP23orPm3, and the lattice parametera0is 86 Å. It is shown that data from previous studies of this phase may be re-intepreted to be consistent with these findings. In view of these conclusions it is clearly inappropriate to refer to the phase as smectic.

ISSN:0267-8292    

DOI:10.1080/02678298608086509

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Structures of the thermotropic mesophases of lead(II) decanoate are reassigned following optical and X-ray diffraction studies. These results, and those of D.S.C., Raman and207Pb N.M.R. spectroscopy, indicate formation of a lower temperature mesophase involving mainly increased lateral disorder, and a higher temperature Lα(smectic A) phase resulting from chain disordering and decreased lead-carboxylate interaction. Comparison of experimental thermodynamic data for the phase transitions with theoretical data in the literature indicates that the entropy change for the lower to higher mesophase transition is dominated by the increase in chain disorder.

ISSN:0267-8292    

DOI:10.1080/02678298608086510

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Nous présentons les premières mesures de viscosité en cisaillement parallèle aux couches dans la phase B hexatique du 65OBC (n-hexyl-4′-n-pentyloxybi-phenyle-4-carboxylate) et dans la phase F du 90.4 (4-n-nonyloxybenzilidene-4′-n-butylaniline). Le comportement pseudoplastique observé dans ces deux phases est analysé en termes de couplage entre l'écoulement et les dislocations. Leur viscosité intrinsèque est déduite des mesures à hautes fréquences. Nous montrons qu'elle est proportionnelle à la longueur de cohérence ζ∥ mesurée antérieurement dans les couches par diffraction des rayons X.

ISSN:0267-8292    

DOI:10.1080/02678298608086511

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The influence of molecular properties on the rotational viscosity, γ1, of nematic liquid crystals is studied. The shear viscosity under flow alignment, ηs, is determined for the same liquid crystals. A significant correlation between both quantities is found. An equation is presented which allows the calculation of γ1from ηswith an error of about 20 per cent for the liquid crystals studied.

ISSN:0267-8292    

DOI:10.1080/02678298608086512

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Dielectric relaxation data are presented for unaligned, partially aligned and aligned thin films of a smectic liquid-crystalline side-chain polymer in the ranges 12 to 105Hz and 299 to 343 K. The unaligned material exhibits a complicated dielectric absorption which has been resolved into two broad components (δ and α processes). The dielectric absorption changes remarkably on alignment of the material such that the δ process is enhanced by a factor of three and the α process is considerably diminished. A consideration is given of the molecular theory for dielectric relaxation in these materials and the variation in dielectric properties is shown to depend on the dipole components μml∥ and μml⊢, the order parameterSfor the mesogenic head groups and the order parameterSdfor the director alignment.

ISSN:0267-8292    

DOI:10.1080/02678298608086513

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This paper considers the flow generated by driving a sample of nematic liquid crystal through a rectangular capillary by application of a small pressure gradient in the presence of a large aligning magnetic field. A theoretical calculation based on the continuum theory of nematics is presented which makes some allowance for non-uniform alignment induced by flow, and allows a more accurate determination of the viscosities corresponding to the three principal configurations in the plane of shear.

ISSN:0267-8292    

DOI:10.1080/02678298608086514

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Changes in the optical transmission induced by electric fields have been studied in a smectic side-chain polysiloxane liquid crystal. The transmission varied from effectively zero, for a highly scattering (opaque) texture, to total, for a homeotropic texture, on increasing the applied voltage across the material. The field-induced textures were durably stored in the smectic phase, enabling the order parameter of the side groups to be studied by dielectric relaxation measurements. For the highly transparent texture, a side group order parameter of 0-92 has been observed.

ISSN:0267-8292    

DOI:10.1080/02678298608086515

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Hydroxypropyl cellulose (HPC) forms liquid-crystalline solutions in both water and methanol. When these solutions are sheared, the banded texture seen in many liquid-crystalline polymers is formed. Detailed optical microscopy of the bands has been carried out, showing that the bands arise from a smooth variation in the orientation of the local extinction directions, and not (as previously suggested in the literature) from sharp kinks. Over a period of time, the bands degenerate to form a new texture, which appears as a square grid pattern of extinction when specimens are viewed between crossed polars. The location of the corners of the squares depends on whether the microscope is focused near the top or bottom surface. When focus is altered to the middle of the sample, the periodicity of the pattern is halved. This texture is identified with the parabolic focal conies previously seen in small molecule smectic and cholesteric materials.

ISSN:0267-8292    

DOI:10.1080/02678298608086516

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We show that the dielectric loss spectra of the planarly-aligned nematic phase of a liquid-crystalline siloxane side-chain polymer consist of a single broad curve, as predicted by theory.

ISSN:0267-8292    

DOI:10.1080/02678298608086517

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

As the result of a printing error the captions for figures 17 and 18 as well as figures 19 and 20 were inadvertently interchanged

ISSN:0267-8292    

DOI:10.1080/02678298608086518

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor