摘要:

Polymer-dispersed liquid crystals (PDLC) are widely used for electro-optic applications such as flexible displays, privacy windows or projection displays. Besides these applications, the confinement of a liquid crystal to small cavities is of fundamental interest. The present paper contains a review of the work on nematic and cholesteric PDLCs. Moreover, some very recent developments are summarized such as the use of ferroelectric liquid crystals for PDLC applications.

ISSN:0267-8292    

DOI:10.1080/02678299408036517

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The synthesis and mesomorphic properties of a homologous series ofN-(2-hydroxy-4-n-alkoxybenzylidene)-4′'-n-decylphenylanilines and their platinum(II) and oxovanadium(IV) complexes are reported. All the ligands and their metal chelates exhibit enantiotropic mesophases, predominantly smectic A and smectic C phases. The transition temperatures and enthalpies have been determined for most of the compounds. The platinum(II) complexes have higher melting points and mesophase thermal stabilities. However, the oxovanadium(IV) complexes have a wider thermal range for the mesophase. Both platinum(II) and oxovanadium(IV) complexes containing only a chain on the biphenyl moiety exhibit a nematic phase.

ISSN:0267-8292    

DOI:10.1080/02678299408036518

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Binary mixture studies involving the chiral nematogens (R)-2-[4-(2′-fluoro-4′-pentylbiphenyl-4-carbonyloxy)phenoxy]propanoitrile and (R)-2-{4-[4-(trans-4-pentylcyclohexyl)benzoyloxy]phenoxy}-1-methoxypropane revealed that these compounds show opposite helical twist senses, reinforcing existing selection rules relating twist sense to chemical structure. Certain mixture compositions displayed a N*RH-N*∞-N*LHtwist inversion sequence, while other compositions showed an induced TGBA* phase mediating the N*LH-S*Aphase transition. This paper presents a complete phase diagram for the binary mixture as determined by polarizing light microscopy and differential scanning calorimetry and gives pitch measurements and determinations of helical twist senses above and below the inversion point.

ISSN:0267-8292    

DOI:10.1080/02678299408036519

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Based on charge transfer interactions with the (chiral) electron acceptor (-)-2-(2,4,5,7-tetranitro-9-fluorenylidenaminooxy)propionic acid ((-)-TAPA), our easily accessible disc-shaped electron rich multiynes (for example,1and2) give rise to two types of cholesteric nematic phases. Thus, thebinarymixture of the nematic discotic (ND) pentakis-(4-methylphenylethynyl)phenyl hexadecyl ether (2) with (-)-TAPA exhibits its twisted variant (N*D). Likewise, but now in aternarymixture, the homologue1—peripherically unsubstituted andnon-mesogenic—with the two electron acceptors (-)- TAPA and 2,4,7-trinitrofluorenone—both alsonon-liquid crystalline—shows cholesteric nematic properties, most probably however of a columnar type (N*C). First results concerning these charge transfer induced cholesteric-nematic properties, including phase diagrams and the helical twist of the two systems presented here, are discussed on the basis of data obtained by polarizing microscopy and differential scanning calorimetry.

ISSN:0267-8292    

DOI:10.1080/02678299408036520

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 attached to the cyclohexyl ring of a variety of two- and three-ring nematic liquid crystals of positive dielectric anisotropy. The new polar two-ring methyl (E)-allyl ethers often possess low melting points, but are not mesomorphic in general. The related three-ring methyl (E)-allyl ethers exhibit high clearing points and wide nematic ranges. 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. This is partially due to the low smectic transition temperatures observed for the methyl (E)-allyl ethers. Selected physical properties of three binary mixtures of a weakly polar standard nematic liquid crystal and three difluoro-substituted (polar) liquid crystals (including the new ethers) differing only in the nature of the terminal chain show that, although some of the methyl (E)-allyl ethers exhibit longer switch-off times in TN cells than those of analogous liquid crystals incorporating either a methyl propyl ether or a 1-(E)-propenyl chain instead of the methyl (E)-allyl ether chain, they are still useful components for nematic mixtures, especially where a wide temperature range is required.

ISSN:0267-8292    

DOI:10.1080/02678299408036521

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Measurements are reported of the ferroelectric polarizationPsinduced in a non-chiral smectic C phase by a variety of chiral dopants having different molecular structural features. Using molecular calculations of contributing dipole moments, ferroelectric order parameters are determined from the experimental results. The relationships between thePsand various other molecular properties are discussed, and it is shown that restricted rotation of the molecule due to its shape and internal energy barriers to rotation can result in relatively high values ofPs. In contrast dipolar groups flexibly attached to a chiral centre may have their contribution toPsgreatly reduced through internal rotation.

ISSN:0267-8292    

DOI:10.1080/02678299408036522

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A mesogenic ester, 4-hexyloxyphenyl 4-vinyl benzoate was synthesized and studied. The synthesis and characterization of bimesogenic molecules employing this ester with oligosiloxane spacers of different lengths are described. The compounds were characterized by IR1H NMR, elemental and thermal analysis, and polarized light microscopy.

ISSN:0267-8292    

DOI:10.1080/02678299408036523

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The synthesis and characterization of a series of new polyacrylates1, containing the azobenzene mesogen spaced from the backbone by a hexamethylene segment and substituted in the 4-position by an alkanoyl chain of variable length, together with those of the relevant precursors are reported. Optical and X-ray analyses provided evidence for the presence of a smectic A mesophase in a fairly broad range of temperature in both polymers and low molar mass compounds. In polyacrylates1, the side-chain substituents were fully interdigitated in a smectic A1structure. The comparison of the transition parameters of polymers1with those of another series of polyacrylates7containing the azobenzene unit substituted in the 4-position by an alkyloxy chain of variable length revealed that the replacement of an oxygen atom by a carbonyl group strongly enhanced the smectogenic character of the azobenzene group.

ISSN:0267-8292    

DOI:10.1080/02678299408036524

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Suspensions of rod-like cellulose crystallites of axial ratio ≈ 20–40, prepared by acid hydrolysis of natural cellulose fibres with sulphuric acid, give stable ordered fluids that display well-formed textures and disclinations characteristic of chiral nematic liquid crystalline phases. The critical volume fraction for phase separation of salt-free suspensions is typically 0.03, with a relatively narrow biphasic region. Because of the negative diamagnetic susceptibility of cellulose, the ordered phase becomes oriented in a magnetic field with its chiral nematic axis parallel to the applied field.

ISSN:0267-8292    

DOI:10.1080/02678299408036525

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Photon correlation spectroscopy of light scattered by director fluctuations from an evanescent optical wave propagating in the nematic liquid crystal 5CB is used to study the interfacial dynamic behaviour of the liquid crystal. The intensity correlation function of light scattered by interfacial orientation fluctuations is measured by illuminating to give a short optical penetration depth within the nematic. These surface scattering correlation functions strongly differ from the bulk correlation function and are interpreted in terms of a nematic surface orientation mode arising from the coupling between the director field and the fluid velocity. It is shown that the analysis of the surface mode gives a method for measuring anchoring energies in liquid crystals. The anchoring energy obtained for rotation of the director away from the rubbing direction about an axis normal to the surface for 5CB at a rubbed nylon surface is 7.14±0.7 × 10-2ergcm-2.

ISSN:0267-8292    

DOI:10.1080/02678299408036526

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor