摘要:

Liquid-crystalline systems consisting of n-alkyl-β-D-glucopyranosides (heptyl to dodecyl) and solutes (water, n-octanol, benzene and methylene dichloride) have been studied by measurement of the deuterium NMR quadrupolar splittings. Particular attention was given to the system of n-octyl-β-D-glucopyranoside (OG)-solute for which the OG-water and the OG-benzene phase diagrams were determined. Information about the orientational order of the aliphatic chain was obtained from deuterium NMR measurements of chain deuteriated OG. The order parameter profiles for the chain in this molecule were calculated using a quantitative theoretical model. A qualitative model served to interpret the dependence of the splittings in different solutes upon their concentration. DSC and preliminary X-ray data supplement the NMR measurements

ISSN:0267-8292    

DOI:10.1080/02678299008033823

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A series of new liquid-crystalline compounds called imidazo [2,1-b]-1,3,4-thiadiazoles has been synthesized. The new compounds contain alkyl, aryl, trans-alkylcyclohexyl groups in positions 2,6 and lateral Br- and CN-substituents in position 5 of the heterocyclic fragment. The new mesogens normally have a wide mesophase range and a high thermal stability (Tc1∼ 300° C). The mesophase type depends significantly on the nature and position of the substituents, in particular the cyclohexane ring. Some chemical, physico-chemical and spectral properties of the new compounds have been investigated. The results are compared with the corresponding characteristics of their aromatic and heterocyclic analogues.

ISSN:0267-8292    

DOI:10.1080/02678299008033824

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Lead(II) salts of aliphatic diacetylenic carboxylic acids are found to form highly ordered smectic phases which thermodynamic data indicate are similar to those reported for the saturated lead(II)alkanoates. At room temperature the materials exist as glassy mesophases which can be readily polymerized by U.V. radiation to yield highly coloured poly(diacetylenes).

ISSN:0267-8292    

DOI:10.1080/02678299008033825

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Two series of asymmetric dimers, the α-(4-n-butylanilinebenzylidene-4′-oxy)-ω-(4-nitroazobenzene-4′-oxy) alkanes and the α (4-dimethylaminoanilinebenzyl-idene-4′-oxy)-ω-(4-nitroazobenzene-4′-oxy)alkanes have been synthesized. Their thermal properties are compared with those of the symmetric dimers, the α,ω-bis(4-nitroazobenzene-4′-oxy)alkanes and the αω-bis(4-n-butylanilinebenzyl-idene-4′-oxy)alkanes. The asymmetric dimers exhibit a semectic A phase for which the ratio of the layer spacing to the molecular length is approximately 0.5; this is thought to imply an intercalated structure in which different parts of the molecule interleave. We propose that this structure is stabilized by a charge transfer interaction.

ISSN:0267-8292    

DOI:10.1080/02678299008033826

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Phenylstearic acid, prepared from oleic acid and benzene, using the Friedel-Crafts reaction, has been confirmed to be a reproducible mixture of twelve positional isomers. Lithium and sodium salts of this acid are semi-crystalline solids which behave in many ways like pure single substances. The thermotropic polymorphism of these soaps has been studied using DSC and polarizing microscopy (as well as X-ray diffraction and7Li NMR spectroscopy for the former soap). Both soaps exhibit characteristic stepwise melting behaviour and form stable reversed hexagonal mesophases at elevated temperatures, in contrast to the lamellar phases exhibited by the unsubstituted soaps.

ISSN:0267-8292    

DOI:10.1080/02678299008033827

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Chiral 1, 2-diphenylethane derivatives have been synthesized and found to form stable chiral Sc phases exhibiting ferroelectric properties. Comparison with diphenylacetylene derivatives revealed that flexibility of the bridging groups between two benzene nuclei strongly influences the stability of mesophases as well as transition temperatures.

ISSN:0267-8292    

DOI:10.1080/02678299008033828

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Several new classes of low polarity, low viscosity and optically weakly anisotropic two and three ring fluorinated liquid crystals with alkenyl side chains are presented. Synergisms which lead to a number of favourable material properties are shown to result from systematic changes of (a) para and lateral fluorination of the benzene ring in the rigid cores, (b) variations of double bond positions in the alkenyl side chains and (c) from replacing cyclohexane core rings by dioxane rings. A broad range of dielectric anisotropies −0.3 < Δε < 13, broad nematic meso-phases, low rotational, λ and bulk viscosities, n, (22°C) < 10cP as well as visco elastic ratios as low as λ/k (22°C) = 3.8 × 10–12m-12s-1 follow; were K = K11 + (K33 - 2K22)/4. As a consequence a wide range of optical threshold voltages V10 and short response times result in field-effect liquid crystal displays. The low ratios κ/Δε of the heterocyclic representatives among the new compounds lead in twisted nematic displays to threshold voltages which are comparably as low as those of (polar) phenylcyclohexane compounds. In agreement with our earlier results pronounced odd-even effects are shown to result from shifting the aklenyl double bond in the new compounds from even to odd side chain sites. This causes Δε to increase by 40 per cent and γ1by 33 per cent. Both odd-even effects are shown to be due qualitatively to the increase of side chain order parameter which is expected from shifting the alkenyl double bond from even into odd sites.

ISSN:0267-8292    

DOI:10.1080/02678299008033829

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Mesogenicity of 3β, 17β-bis(4-n-alkoxybenzoyloxy) androstene homologues (BABA) (carbon No. of alkoxy group, n, = 1–10) were studied by use of D.S.C. and a polarized microscopy. It was found that the n = 4–10 compounds of BABA have one cholesteric mesophase with high thermal stability enantiotropically, and that the n = 1–3 compounds decompose just above the melting point. Mesogenicities of BABA and several testosterone and estrone derivatives were also discussed from the perspective of chemical structure and shape. The presence of an intramolecular long-range dipole coupling in two alkoxybenzoyloxy chromophores is found in BABA from CD spectral studies.

ISSN:0267-8292    

DOI:10.1080/02678299008033830

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Six p-alkoxy and eight p-alkylbenzoates of 1,2-(p-hydroxyphenyl)ethane were synthesized for potential use as stationary phases in gas-liquid chromatography. All the p-alkoxy derivatives were nematic. The first five members of the alkyl series were nematic and the rest exhibited both smectic and nematic character. Most possess the desired combination of a wide liquid-crystalline temperature range and a high mesomorphic-isotropic transition temperature. The nematic-isotropic transition temperatures and entropies show the usual alternations characteristic of a high-melting series.

ISSN:0267-8292    

DOI:10.1080/02678299008033831

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A new class of mesogen formed by three chain diols is described. These compounds consist of a central part to which three aliphatic chains of various length (n = 4–14) are attached at one end and two hydroxy groups at the other. X-ray scattering, dilatometric measurements, dielectric and Kerr relaxation studies were carried out. Both X-ray investigations, dielectric and electro-optic studies revealed that the molecules are aggregated in the isotropic fluid state and that hydrogen bonding and dipole correlation contribute to this aggregation. Columnar assemblies of up to several hundred molecules are orientationally correlated in the isotropic fluid phase. Correlated reorientations occur in the presence of external electric fields. The X-ray data show that the aggregates pack in a hexagonal way at lower temperatures giving a structure which strongly resembles that of the hexagonal disordered columnar phase. This anisotropic phase can be quenched to a glassy liquid-crystalline state. It is evident that the mesogenic properties of this new class of compounds are a function of the disc-like shape of the aggregates rather than the shapes of the individual molecules.

ISSN:0267-8292    

DOI:10.1080/02678299008033832

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor