摘要:

In the analysis of spectroscopic data from liquid crystals consisting of either small molecules or polymer chains, it is essential that account be taken of some particular features due to the oriented nature of the phases investigated. For liquid crystal polymers some specific additional problems arise, such as the difficulties in orienting main-chain liquid crystal polymers, the occurrence of the glass-liquid transition and secondary transitions. These questions are first discussed, then the studies performed using2H and13C N.M.R., E.S.R. and dielectric relaxation on both side-chain and main-chain liquid crystal polymers are presented.

ISSN:0267-8292    

DOI:10.1080/02678298808086558

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The kinetics of enolization of acetone, 3-pentanone, and 6-undecanone have been studied in lyotropic systems in the isotropic, nematic, and lamellar phases. The data, analysed in terms of spontaneous and acid-catalyzed rate constants, do not show any relevant influence of the physical nature of the phase. Effects are instead observed in relation to the length of the alkyl chains of the ketones and the type of the amphiphilic molecule. 6-undecanone has a surprising effect in stabilizing ordered mesophases.

ISSN:0267-8292    

DOI:10.1080/02678298808086559

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

It is shown that the fluctuations in the intensity of light transmitted by planar aligned nematic liquids between polarizers is determined by the rotational viscosity alone at sufficiently high frequency. The technique is applied to the determination of the viscosity of polymer liquid crystal mixtures. The most viscous mixture which was successfully aligned (60 per cent polymer) has a viscosity 230 times larger than the cyanobiphenyl monomers.

ISSN:0267-8292    

DOI:10.1080/02678298808086560

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We present the phase diagram of a binary system of two nematogenic terminal, non-polar compounds in which an induced smectic A phase appears over a large concentration–temperature range. X-ray measurements give evidence that the layer spacing,d, of this induced smectic A phase is clearly larger than the average molecular length,L(d/L:112 … 1.23). The unusual experimental results are interpreted on the basis of a pronounced steric interaction by which gaps between the large double swallow-tailed compounds are filled with small molecules. We propose theterm filled smectic A phasefor this new type of induced phase.

ISSN:0267-8292    

DOI:10.1080/02678298808086561

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The thermodynamic stability of micro-clusters in a membrane built-up by charged and uncharged lipid molecules is discussed. A simple variational function is proposed in order to describe the essential structure of such lipid domains. Solvent-screened electrostatic repulsion between the lipid ionic head groups, short-range forces between the lipid hydrophobic taisl and entropic effects are taken into account. The stability conditions as well as the composition and the size of the lipid micro-domains are calculated and expressed as a function of molecular parameters for the membrane and its environment (for example, short-range forces, surface charge density of the lipid bilayer, ion concentration of the electrolyte solution in contact with the lipid membrane and temperature). As an application, the effect of micro-domain formation on the number of adsorbed ions on a charged lipid membrane has been calculated.

ISSN:0267-8292    

DOI:10.1080/02678298808086562

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Measurements of the splay, twist, and bend elastic contants have been made on a series of lyotropic liquid crystals of poly-γ-benzyl-l-glutamate formed in concentrated solutions of non-aggregating solvents. The solvent dependence of the persistence length of the macromolecule was also examined. The influence of solvent on the elastic properties of the liquid crystal is distinguished from that of polymer conformation. With such separation of variables, the results are broadly in accord with predictions of flexible rod models. The variation of the elastic constants with molecular weight, however, depends upon solvent.

ISSN:0267-8292    

DOI:10.1080/02678298808086563

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The synthesis of a new discotic mesogen, 2,3,7,8,12,13-hexa(octadecanoyloxy)-truxene is reported. This new compound has been studied using polarization microscopy, differential scanning calorimetry, small angle X-ray scattering and adiabatic calorimetry. The results are compared with those of two other truxene derivatives from the same series: 2,3,7,8,12,13-hexa(decanoyloxy)truxene and 2,3,7,8,12,13-hexa(tetradecanoyloxy)truxene. Refractive index measurements have been performed on these three truxene derivatives as a function of temperature. A re-entrant isotropic phase has been observed in 2,3,7,8,12,13-hexa(octadecanoyloxy)truxene. This is the first report of such a phase in a pure mesogen. We also report measurements of the ratio of the Frank constants for splay and bend in the nematic regime of this new mesogen as a function of temperature using the magnetic Frederiks transition technique.

ISSN:0267-8292    

DOI:10.1080/02678298808086564

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We report measurements of the dynamics of the magnetic Frederiks transition in nematics consisting of disc-like molecules. In this paper the results are presented for three 2, 3, 6, 7, 10, 11-hexakis(p-alkoxybenzoyloxy)triphenylenes, which exhibit a normal nematic phase, and for three 2, 3, 7, 8, 12, 13-hexa(alkanoyloxy)truxenes, which exhibit an inverted nematic phase. We find that the thermal dependence of a bend viscosity coefficient (γ*1) can be accurately described by the expression, γ*1∼S2exp (Ea/kT). The absolute value of γ*1is found to be higher (by a factor of 10–100) than is commonly encountered in nematics consisting of rod-like molecules.

ISSN:0267-8292    

DOI:10.1080/02678298808086565

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Over forty 4-alkoxyphenyl 4-alkoxybenzoates incorporating an olefinic double bond in one carbon chain and an optically active centre in the second (methyl branched) chain have been prepared. The effect of chain length and the position of the chiral centre on the liquid crystal transition temperatures of the esters has been investigated systematically. Apart from one important exception the double bond was maintained in a terminal position of the carbon chain. Several of the new esters exhibit an enantiotropic chiral smectic C mesophase at and just above room temperature.

ISSN:0267-8292    

DOI:10.1080/02678298808086566

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Approximately thirty 4-(alkenyloxy)phenyl 4′-alkyl/alkoxy-4-biphenyl-1-carboxylates incorporating a chiral centre at the point of branching of the terminal alkyl/alkoxy chain have been synthesized. The three carbon chains investigated were 2-methylbutyl, 3-methylpentyl and 2-methylbutoxy. The configuration of the chiral centre is (S) in each case. The effect of the alkenyloxy chain length on the liquid crystal transition temperatures of the three homologous series prepared has been studied systematically. Chiral smectic C and chiral nematic mesophases, as well as a smectic A mesophase in several cases, were observed over a wide temperature range for most of the esters prepared.

ISSN:0267-8292    

DOI:10.1080/02678298808086567

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor