ISSN:0267-8292    

DOI:10.1080/02678298808086624

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Polymer liquid crystals can occur as polydomain materials where the domain size may be tens of microns. While the material within each domain may be characterized by a common order parameter, the directors of the domains can be more or less randomly distributed. Since the transition from polydomain to monodomain material only involves the removal of grain boundaries and the alignment of directors, the free energy change must necessarily be small. Such a transition can readily be achieved, therefore, by the action of any external field: electrical, magnetic, stress or surface. In this work optical photomicrographs of polymeric liquid crystals with widely varying and in some cases well controlled morphologies are presented. Probable dependence of rheological behaviour on morphology is also discussed. Such dependence is expected to be considerable under certain conditions. Due to experimental and sample limitations, however, direct correlations of rheology and morphology are sparse. Morphological consequences for the rheology of liquid-crystalline materials can be exemplified by the following possibilities. In contrast to the case of isotropic melts, wall effects can be non-negligible. Zero shear rate rheological parameters are not expected to be uniquely defined quantities since the domain sizes are large and the director may not be effectively averaged over typical sample dimensions. Non-zero shear-rate measurements of rheological parameters is effected by the propensity of: (1) individual domain directors to align under the influence of a stress field and (2) flow alignment to dominate surface-induced alignment above some critical shear rate. The effects might be manifested by a non-newtonian regime as well as yield stress behaviour and thixotropy. The kinetics of relaxation from mono- to poly-domain material has implications for the dynamic response and rheological hysterises of the material.

ISSN:0267-8292    

DOI:10.1080/02678298808086625

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The anisotropy of the static electric permittivity and conductivity for the homologous series of nematics: 4-(trans-4′-n-alkylcyclohexyl)isothiocyanato-benzenes (n-CHBT) forn= 3–10 have been measured. It is shown that the odd-even effect in the dielectric anisotropy Ac is related to the perpendicular component of electric permittivity. The odd-even effect is found inn-CHBT for both the anisotropy in the conductivity and the activation energy for ionic movement.

ISSN:0267-8292    

DOI:10.1080/02678298808086626

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The synthesis is reported of fifteen three-ring 2,5-disubstituted pyridines and two pyridine-N-oxides where the pyridine rings carry a variety of alkyl, aryl, cyclohexyl, cyclohexylethyl and fluorinated-aryl substituents. The mesomorphic transition temperatures for these compounds have been measured; all the compounds show enantiotropic phases. The different substituent effects are discussed and comparisons are made with previous work on analogous systems where the hetero-function is replaced by C-F.

ISSN:0267-8292    

DOI:10.1080/02678298808086627

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Lead(II) carboxylates with even chain lengths from octanoate to octadecanoate have been investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, and dilatometry, together with Raman, infrared, and207Pb N.M.R. spectroscopy. The reassignment of the high temperature mesophase as smectic A (Lx) for the octanoate to dodecanoate is confirmed. This phase is most stable for the decanoate. The intermediate temperature mesophase is a highly ordered three dimensional lamellar structure based on ionic layers. The alkyl chains in this phase are partially disordered (melted) through the introduction of gauche conformations and show decreased lateral interactions; however, they remain largely in an extended conformation due to the constraints imposed by the ionic network. Melting of the alkyl chains occurs therefore in more than one step. Re-cooling to the crystalline phase appears to result in a different polymorphic crystalline form (albeit still lamellar) from the original.

ISSN:0267-8292    

DOI:10.1080/02678298808086628

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

It was found that each of the tetrakis(n-alkyldithiolato)dinickel(II), (Cn-DTA)4-Ni2, complexes wheren-alkyl isn-pentyl throughn-dodecyl, exhibits a broken-fan texture on cooling from an isotropic liquid, and that the phase gave a characteristic lamella structure X-ray diffraction powder pattern. Furthermore, the infrared spectrum of this phase is more similar to that of the isotropic liquid than that of the crystal. Therefore, the phase can be described as a monotropic lamella mesophase. Interestingly, each of the complexes of bis(n-alkylxanthato)nickel(II), (Cn-Xan)2Ni, (n= 5, 7, 9, 11) exhibits double (triple) melting behavior via the isotropic liquid, whereas each of the complexes of (Cn-Xan)2Ni (n= 4, 6, 8, 10, 12) shows ordinary single melting behavior. Such unique double melting accompanied by an even-odd effect appears to be the first example of this in the long chain substituted compounds. Each of the complexes of (Cn-Xan)2Ni (n= 9, 11, 12) has a monotropic lamella mesophase exhibiting a large broken fan texture.

ISSN:0267-8292    

DOI:10.1080/02678298808086629

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We present a simple method by which the variation of the hypersound velocity with the angle between the liquid crystal director and the scattering plane is fitted to theory. Combinations of bulk elastic constants can be obtained together with a value for the second sound velocity. This method is used to study the smectic A phase of 4-n-octyl-4′-cyanobiphenyl. We compare our results with previous work.

ISSN:0267-8292    

DOI:10.1080/02678298808086630

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Scanning dilatometric and calorimetric measurements were performed in order to obtain information on correlations between various phenomena involving a lipid vesicle. Scanning dilatometry has been shown to be a fast and reliable tool which gives complementary information to that obtained using differential scanning calorimetry and also, provides a means with which to follow dynamic processes without the introduction of perturbing probes into the lipid matrix. The systems examined were vesicles built up from mixtures of neutral and charged lipids in the presence of mono- and divalent inorganic cations. The studied processes were the gel-liquid crystal transition, lateral phase separation in mixed lipid vesicles and fusion between vesicles.

ISSN:0267-8292    

DOI:10.1080/02678298808086631

出版商:Taylor & Francis Group    

年代:1988

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:10.1080/02678298808086623

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor