摘要:

The disclination strength defined on the boundary of textures generated by recently proposed simple modelling methods appears to be the sum of the strengths of primitive disclinations inside the boundary. In this paper, a rationalization is provided for these observations in two dimensions using an analytical expression for the conservation law for wedge type disclinations.

ISSN:0267-8292    

DOI:10.1080/02678299408029171

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Tolane-based liquid crystal materials with three different terminal groups: trifluoromethyltolanes, cyanotolanes, and nitrotolanes, and with different chain lengths of alkenyloxy groups, have been synthesized. The phase behaviour of these liquid crystal materials has been characterized by differential scanning calorimetry, optical polarized light microscopy and X-ray diffraction. The mesophase behaviour of the materials was shown to be significantly influenced by the polarity of the terminal groups. The trifluoromethyltolanes exhibit an enantiotropic smectic E mesophase and the cyanotolanes exhibit a monotropic nematic mesophase. The most polar among the three types of liquid crystal material; the nitrotolanes do not display any liquid crystalline phases, except for the homologue with an eleven methylene unit chain.

ISSN:0267-8292    

DOI:10.1080/02678299408029172

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We propose the following: on the boundary of a nematic liquid crystal, the function which describes the molecular orientation is subject to a further symmetry condition, besides that reflecting apolarity. This additional symmetry delimits a class of biaxial states; within that class we study a model problem for a thin layer in which the anchoring energy prevails over the elastic energy in the presence of an electric field. We show that, when the anchoring and electric energies favour uniaxial states with optic axes at right angles, the equilibrium configuration migrates from one state to the other, traversing a whole family of biaxial states as the strength of the electric field increases.

ISSN:0267-8292    

DOI:10.1080/02678299408029173

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We have introduced an oxygen atom and a carbon-carbon double bond with atrans-configuration (E) into the terminal alkyl chain of a wide variety of liquid crystalline cyclohexane derivatives to produce a variety of new methyl (E)-allyl ethers. The melting points and tendency to form smectic mesophases are often low, while nearly all of the compounds prepared exhibit a nematic phase. Thus, even two-ring derivatives can exhibit nematic phases over a wide temperature range (≤80°C), sometimes starting below room temperature (Tm≈10°C). Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. Thus many of the new methyl (E)-allyl ethers exhibit nematic phases over a wider temperature range than the corresponding materials with an unsubstituted alkyl chain attached to the cyclohexyl ring. The new compounds are easily prepared from known starting materials. Many intermediates are themselves liquid crystalline. This allows investigation of the relationship between liquid crystal transition temperatures and the nature of the terminally substituted alkyl chain (for example, incorporating C˭C, OH, CO2C2H5and OCH3groups).

ISSN:0267-8292    

DOI:10.1080/02678299408029174

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The phase behaviour of binary mixtures of self-assembled tapering molecules based on monoesters of oligooxyethylene glycol and 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoic acid, their corresponding polymethacrylates, and of 4′-methyl (benzo-15-crown-5)-3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate within their hexagonal columnar mesophase (Φh) is described. The binary blends between molecular tapers co-assemble into a single supramolecular column resulting in isomorphism within their Φhmesophase over the entire range of composition. The binary blends between polymethacrylates containing tapered side groups co-assemble into a single Φhphase only when the columns of the parent polymers are of similar diameters. This results in binary mixtures which are isomorphic within the Φhmesophase over the entire composition range. When the diameters of the columns formed by the parent polymers are dissimilar, isomorphic mixtures are obtained only over a narrow range of composition. Binary mixtures between molecular tapers and macromolecular systems containing tapered side groups co-assemble into a single column to the extent that intercalation of the molecular taper, within the column formed by the macromolecular system containing tapered side groups, is permissible. In all systems increased intracolumnar interactions can be induced by complexation of CF3SO3Li by the oligooxyethylenic receptors leading to isomorphism in otherwise non-isomorphic mixtures. Ternary mixtures between molecular tapers with non-specific oligooxyethylenic receptors and specific crown ether receptors and CF3SO3Na as the third component are non-isomorphic within their Φhphase due to preferential complexation of the alkali metal cation by the column of the crown ether containing the molecular taper. This results in two columns of dissimilar diameters, which are isomorphic in the Φhphase only within a limited range of composition.

ISSN:0267-8292    

DOI:10.1080/02678299408029175

出版商:Taylor & Francis Group    

年代:1994

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:10.1080/02678299408029160

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor