摘要:

The thermotropic mesomorphism of tetrakis(μ-(2,2-(dioctyl(acetato))-O,O′)bis-[copper(II)] has been investigated by optical microscopy and X-ray diffraction. This compound was found to form a hexagonal discotic phase analogous to those reported for the copper(II) salts ofn-alkanoic acids, but in contrast to these materials the mesophase of the branched chain compound was found to extend to below room temperature. Complexation of the copper(II) branched chain carboxylate with the difunctional ligands pyrazine and 4,4′-dipyridyl resulted in liquid-crystalline materials whose mesophase structure could not be established. The possibility of these complexes existing as polymeric/oligomeric entities is discussed.

ISSN:0267-8292    

DOI:10.1080/02678299008047349

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Two novel types of transition-metal-containing liquid crystals, bis(p-n-koxydithiobenzoato)nickel(II) (abbreviated as (CnO-DTB)2Ni), and (p-n-alkoxydithiobenzoato)(p-n-alkoxyperthiobenzoato)nickel(II) (abbreviated as (CnO-DTB)(CnO-PTB)Ni), were synthesized. It was found that the (CnO-DTB)2Ni complex forn= 8 hassmecticH and C mesophases, and that the (CnO-DTB)2Ni complexes forn= 4 and 8 easily transform into the corresponding monoperthio complexes,nO-PTB)Ni, by heating at temperatures between 230°C and 285°C. It was confirmed that the transformation originates from an intermolecular reaction between the (CnO-DTB)2Ni complexes at high temperatures, and that the origin of the extra sulphurs in the resulting (CnO-DTB)(CnO-PTB)Ni complexes is the neighbouring (CnO-DTB)2Ni complexes. Interestingly, each of the (CnO-DTB)(CnO-PTB)Ni complexes (n= 4 and 8), hasnematicmesophase and exhibits a unique double melting behaviour via the nematic phase, which is the first example in liquid crystals. The reversible transformation between theblue smectic rod-like(CnO-DTB)2Ni complex and thered nematic Λ-like(CnO-DTB)(CnO-PTB)Ni complex is possible.

ISSN:0267-8292    

DOI:10.1080/02678299008047350

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Stationary states of surface stabilized ferroelectric liquid crystal layers in an electric field are analysed by use of the Taylor expansion method based on catastrophe theory. Two kinds of director distribution within the flat smectic layers are taken into account: the uniform and the presplayed one. The butterfly catastrophe describes the properties of the cells correctly. The results have a qualitative character. Two categories of transitions can be predicted: switching between stable states characterized by opposite uniform orientations of the polarization vectors, and deformation of the director field which relaxes after removing the field. The threshold field strengths are found and the role of the system parameters is investigated.

ISSN:0267-8292    

DOI:10.1080/02678299008047351

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Six varieties of liquid-crystalline side-chain polymers, poly (cholesteryl ω-(methacryloyloxy)alkanoates) (p-ChMO-n, n= 1,2,3,4,5,7, the carbon number of the alkyl chain), were studied by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). On and after the first cooling run from the isotropic state, these polymethacrylates gave the same smectic phase. However, on the first heating run for virgin samples, unique phenomena were observed, similar to those frequently observed on the first heating run for thermotropic liquidcrystalline polymers. The thermal properties of the first heating run for these six polymers showed different tendencies betweenpChMO-n (n-1–3) andpChMO-n(4–7). Although the DSC curve ofpChMO-n (n= 4, 5 and 7) exhibited the melting and clearing points on the first heating run, the DSC curve ofpChMO-n (n= 1,2 and 3) exhibited an exothermal peak between the glass transition and the clearing point on the first heating run. This difference, probably due to the difference in the spacer length of these polymers, was investigated quantitatively by small-angle X-ray scattering by which the micro-change of the packing structure of the side chains of the polymers was traced.

ISSN:0267-8292    

DOI:10.1080/02678299008047352

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Electrooptical investigations on a ferroelectric liquid crystal (DOBAMBC) were carried out on a well aligned sample in a 2 μm cell. On the basis of these measurements the complete average director movement during a switching process caused by an electric field can be calculated and will be discussed. The thermodynamic potentials at the SA*-SC*phase transition were determined from the experimental results with a modified Landau theory. They serve as a basis for a discussion of the phase transition and the influence of the surface orientation. Some preliminary results were obtained concerning the electrooptical behaviour of the SH*phase.

ISSN:0267-8292    

DOI:10.1080/02678299008047353

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A discotic triphenylene monomer as well as a dimer and a main chain polymer, all substituted with heptyloxy side groups, were doped with an electron acceptor (2,4,7-trinitrofluorenone (TNF)) to give charge transfer complexes. These doped systems were aligned in a magnetic field, thus proving their liquid crystallinity.2H NMR measurements show that the electron acceptor molecules are incorporated into the columns built of triphenylene cores. In the charge transfer complex with the triphenylene monomer almost all the electron acceptor molecules stack in the columns even close to the clearing temperatureT1, while for the dimer and especially for the polymer a significant fraction of the TNF molecules exhibits isotropic motion, which is attributed to their location in the region between the columns, already way belowT1. This isotropically distributed part increases on approachingT1. Fast rotation of the discs around their column axes takes place in the monomer and is quenched in the dimer and the polymer, due to the interlinking of the columns by the spacer. The electron acceptor molecules, on the other hand, exhibit free rotation in all samples, even in the charge transfer complexes with the triphenylene dimer and polymer. In the side group labelled triphenylenes increased2H NMR spectral narrowing is detected in the charge transfer complex samples compared with the corresponding pure triphenylenes. This indicates higher side group mobility in the doped systems, since the incorporation of TNF molecules increases the spacing between the discotic units.

ISSN:0267-8292    

DOI:10.1080/02678299008047354

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

An interpretation of the pitch and time dependence of diffusion in the cholesteric liquid crystalline phase is proposed. Experimental results on nematics twisted by chiral dopands are discussed. The model predicts a decay of the translational diffusion coefficientDpin the helix direction with the observation time and a decrease ofDpwith shorter pitch lengthPo, in accord with experiment. From comparison with experimental data it is concluded that rotational diffusion in these samples is a collective phenomenon.

ISSN:0267-8292    

DOI:10.1080/02678299008047355

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We have used chiral compounds with very high helical twisting power as components in induced-cholesteric mixtures in order to obtain new blue phase systems. In one of these mixtures anunusual large blue phase temperature rangeof more than 10 K was observed. The lattice constant of the BPI in this systemincreasesstrongly with increasing temperature, a behaviour observed for the first time. The threshold voltage for the field-induced BP/cholesteric phase transition in this mixturedecreaseswith increasing temperature. Thus thereentrantphase sequence cholesteric phase-blue phase-cholesteric phase-isotropic phase can be observed with increasing temperature if an electric field is applied to the sample.

ISSN:0267-8292    

DOI:10.1080/02678299008047356

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Three new series of cyanoaryl 4-alkylthioxybenzoates have been synthesized and characterized. The 4-cyanophenyl series displays only transient mesomorphic properties while the 6-cyano-2-naphthyl and 4-cyanobiphenyl series exhibit the classical nematic and smectic A phases; a reentrant nematic phase is also found in the latter. Two other new series in which the position of the sulphur atom in the central rigid core has been varied were also prepared: the 4–[4′-cyanobenzoyloxy]-phenyl 4-alkylthiobenzoates and 4–[4′-alkylbenzoyloxy]phenyl 4-cyanothiobenzoates. As in the analogous benzoate series, the reentrant phenomenon with the sequence C, SAre, Nre, SA, N, I is observed with the nonyl derivatives. Comparisons between the alkoxybenzoates and the alkylthioxybenzoates are given.

ISSN:0267-8292    

DOI:10.1080/02678299008047357

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Sept séries homologues dérivées de la structure 4-n-butylN-(4′-n-alkoxy 4-benzoyloxybenzylidène) aniline ont été synthétisées en introduisant sur le cycle central un groupement hydroxyle en position 2 et des groupements nitro en position 3 ou 5. L′étude comparée des températures de transition permet de conclure que l′introduction du groupement hydroxyle aide à la formation de la phase mésogène et que le groupement nitro, bien que diminuant les plages de nématicité, peut conduire à l′obtention de cristaux liquides possédant un motif thermochrome.

ISSN:0267-8292    

DOI:10.1080/02678299008047358

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor