摘要:

The lyotropic polymorphism of a series of alkyl esters of acyl-L-carnitine has been studied by optical polarizing microscopy and X-ray diffraction. The different structures observed as a function of concentration and temperature have been characterized and their topology determined. As a result, two different phase sequence patterns have been detected: esters of normal alcohols bearing an alkyl chain of 6 or more carbon atoms in the acyl substituent display only a lamellar phase, while compounds which bear a relatively short alkyl chain (4 or less carbon atoms) show in addition non-lamellar type I hexagonal and cubic Q230phases. From the analysis of the areas-per-molecule at the polar/apolar interface, the ability of the compounds investigated to form not only non-lamellar phases, but also direct micelles in isotropic solution has been related to the structural characteristics of the molecules. Curved, convex interfaces (in micelles and in non-lamellar phases) are possible only for the most polar acylcarnitines which have a relatively short alkyl chain, so that they behave like single chain surfactants; the most paraffinic derivatives, which have a relatively long alkyl chain, are effective double chain surfactants and then generate only quasi-planar interfaces.

ISSN:0267-8292    

DOI:10.1080/02678299508031992

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have investigated the mesomorphic behaviour of a partially deuteriated side chain LC polymethacrylate, poly[4-[6-methacryloyloxyhexyl-oxy]-4′-methoxyazobenzene], by means of2H NMR, DSC and optical microscopy. Evidence for a phase transition occurring in the middle of the nematic phase has been found.

ISSN:0267-8292    

DOI:10.1080/02678299508031993

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The phase behaviour and the structural characterization of a new series of linear dimeric and cyclic tetrameric molecules which contain three distinct parts, a cyanobiphenyl aromatic core (A), a paraffin chain (P) and a central siloxane group (B) with the A-P-B-P-A sequence, are described. Incompatible with one another, these parts tend to locate themselves in three separate sub-layers superposed in a partially bilayered smectic A structure. Each sub-layer adapts its internal structure in order to be appropriate for superposition, as in the case of organosiloxane molecules with the A-P-B sequence reported previously.

ISSN:0267-8292    

DOI:10.1080/02678299508031994

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Optical rotation and circular dichroism measurements performed in the pretransitional isotropic region above the chiral smectic phases TGBA*, TGBC*, S*C, and S*Aexhibited by 1-alkylalkyl 4′-(4″-n-alkoxyphenylpropioloyloxy)biphenyl-4-carboxylates are reported. These results revealed a high degree of increasing chiral ordering on cooling in the isotropic phase, particularly in the temperature region where a broad DSC peak appears. However, the behaviour of the pretransitional optical activity was unlike that commonly observed for chiral nematic or blue phase compounds and did not follow a simple Landau-de Gennes temperature dependence. Characteristic features of the pretransitional optical activity may aid in understanding the local structure of chiral smectic phases. Electric fields did not seem to influence the results significantly, but strong electric field-induced optical rotation behaviour was demonstrated for a mixture constituted of the laterally fluorinated propiolate ester component and a nematic with a large positive dielectric anisotropy. These field-induced results could be fitted to expressions from the existing theory of pretransitional optical activity. Circular dichroism studies at low temperatures were performed for two compounds in dilute solution and were found to exhibit very large changes in their extinction coefficient at wavelengths in the ultraviolet region, which may indicate strong chiral interactions even in dilute isotropic solutions of these materials.

ISSN:0267-8292    

DOI:10.1080/02678299508031995

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Thirty compounds, ten members of each of three homologous series of esters derived from 4-hydroxy-4′-n-octyl-, -nonyl-, and -decyl-biphenyl and the 5-n-alkylthiophene-2-carboxylic acids (methyl through to decyl homologues) have been prepared. The liquid crystal properties of these esters, which show extensive smectic polymorphism, have been investigated by thermal optical microscopy, differential scanning calorimetry, and miscibility studies. Four members of the corresponding 4-n-alkylbenzoates have also been prepared in order to compare their liquid crystal behaviour with the 5-n-alkylthiophene-2-carboxylate counterparts: both smectic and nematic thermal stability are higher for the 4-n-alkylbenzoates, by 30.6° and 36.8° C, respectively.

ISSN:0267-8292    

DOI:10.1080/02678299508031996

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The twisting power of chiral probes in nematics is interpreted in terms of a shape model, in which the surface elements of the solute molecules tend to align with the local director. The theoretical treatment is based on a previous approach, suitable for relating order parameters in nematics to molecular shape, and leads to the definition of a molecular pseudo-tensor whose orientational average determines the pitch and handedness of the helical macrostructures. Results of numerical calculations performed for distorted biphenyl and binaphthyl molecules are in agreement with the experimental results.

ISSN:0267-8292    

DOI:10.1080/02678299508031997

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0267-8292    

DOI:10.1080/02678299508031981

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor