摘要:

The intrinsic uniform and non-uniform contributions to the anisotropic part of the surface energy are considered. Our analysis shows that the uniform part can be separated into an intrinsic and an extrinsic term. The first one is due to the nematic-nematic interaction only, whereas the second one is due to the nematic-substrate interaction. They are found to be of the same order of magnitude (≈1 erg cm2). The non-uniform part takes its origin from the spatial variation of the elastic constants. By means of a semi-microscopic model it is shown that, in the framework of perfect nematic order, the extrapolation length of the elastic origin is microscopic. On the contrary, if the spatial variation of the scalar order parameter is taken into account, simple calculations indicate that the extrapolation length is of the order of the coherence length in the nematic phase.

ISSN:0267-8292    

DOI:10.1080/02678299608031116

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A detailed investigation has been reported of the electroclinic behaviour in the smectic A* phase of eleven mixtures made up of a commercial achiral smectic C host and strongly chiral alkoxybiphenyl-phenyl carboxylate dopants. A new technique was used to measure the induced tilt angle as a function of electric field and temperature. For all the mixtures, the electroclinic response followed a Curie-Weiss type temperature dependence for measurements performed well away from the smectic A* to smectic C* phase transition temperature. The strength of the electroclinic response was evaluated for each mixture by determining the temperature independent ratiok/a(i.e. the electroclinic coupling susceptibility,kdivided by the susceptibility coefficient controlling the induced tilt,a). Analysis of the results showed thatk/aof the mixtures was dependent on the type and position of the electronegative or polar substituents that affected the net dipole moment of the chiral dopants. In fact, the value ofk/awas largest when fluorine was replaced by hydrogen in the lateral position and at the chiral centre. Furthermore, relatively short alkyl chains (e.g. C6H13) at the chiral centre were preferred to longer ones (e.g. C10H21) for a larger electroclinic response.

ISSN:0267-8292    

DOI:10.1080/02678299608031117

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

X-ray measurements on hexakis(4-(4′-alkyloxy)biphenoxy)cyclotriphosphazenes [PN-(OC6H4C6H4OCnH2n+ 1)2]3(HACP,n= 7–9), confirm the previous mesophase identification. The apparent molecular length measured in the mesophase compares to twice the length of an alkyloxybiphenyl side group. Specific features are added to the usual features of the nematic and smectic diffraction patterns which show that the molecular arrays in directions parallel and perpendicular to the director both reflect the peculiar shape of the cyclotriphosphazenes.

ISSN:0267-8292    

DOI:10.1080/02678299608031118

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Chiral 2-amino-4-alkoxy-5-nitrobenzoate and 5-amino-4-alkoxy-2-nitrobenzoate derivatives as well as the corresponding biphenyl derivatives were synthesized. Some of them were also derivatised to the corresponding acrylates and polyacrylates. Many of the new substances exhibit a large spontaneous polarization and large second order NLO coefficients. In addition some of them show a broad range S*cphase. All these properties depend strongly on small changes in the molecular structures. Here we present the synthesis of these novel NLO FLC materials and discuss some of their properties.

ISSN:0267-8292    

DOI:10.1080/02678299608031119

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A new series of chiral Schiff's bases containing 2-hydroxybenzilideneaniline moieties and their copper complexes were synthesized and studied by differential scanning calorimetry, polarized optical microscopy, X-ray diffraction and EPR measurement. The results show that most of the Schiff's bases and only two of the copper complexes exhibited chiral smectic liquid crystal phases.

ISSN:0267-8292    

DOI:10.1080/02678299608031120

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A macroscopic model for incompressible homogeneous (single phase) binary nematic mixtures, under isothermal conditions is given. The rheological model is a generalization of the standard Ericksen's nematorheological model for single component uniaxial rod-like nematic liquid crystals. Its special cases include single component orthorhombic biaxial nematics and single component uniaxial nematics. The theory is used to formulate rules for the rotational viscosity and the reactive parameter of nematic mixtures in the presence of weak flows. The predicted mixture rules for the reactive parameter and rotational viscosity are analysed as a function of concentration and rotational viscosity ratio for various monomeric and polymeric mixtures, and for rod-rod, disc-disc, and rod-disc nematic mixtures. The mixture rules are used to compute alignment phase diagrams and alignment transition (orientational instability) thresholds.

ISSN:0267-8292    

DOI:10.1080/02678299608031121

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Stilbenes were attached to a quartz surface at their 2-position by silylation through a spacer to determine the capability to regulate an azimuthal alignment of a nematic liquid crystal by irradiation with linearly polarized light. Liquid crystal molecules aligned perpendicular to the direction of polarization plane of the actinic light, just as in the case of surface azobenzenes. The efficiency of the photoregulation was influenced by excitation wavelength and hence related with anE/Zisomeric ratio in a photostationary state. The irradiation with 260 nm polarized light resulting in theE-isomer as a major component in the photostationary state gave better optical quality of a photoaligned texture when compared with 330 nm irradiation, suggesting that the orientation of liquid crystals is induced by the rod-likeE-isomer. Discussion was made on the possibility of the role of phenanthrenes, which were formed upon prolonged irradiation, in the liquid crystal photoalignment.

ISSN:0267-8292    

DOI:10.1080/02678299608031122

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The surface of a silica substrate plate was modified with a cinnamate moiety having a triethoxysilyl group at theortho-position through a spacer. The plate was employed to assemble a cell filled with a nematic liquid crystal and exposed to linearly polarized 259 nm light to obtain homogeneous alignment. The direction of the alignment was perpendicular to an electric vector of the actinic light. On the contrary, the exposure of the cell to polarized light at 330 nm did not result in homogeneous alignment while the actinic light caused the disappearance of the chromophore. This wavelength effect on the azimuthal photoalignment suggests that the surface-assisted liquid crystal orientation is triggered by the reorientation of theE-isomer of the cinnamate group. This is in marked contrast to a proposed mechanism of a photoalignment by a thin film of a poly(vinyl cinnamate) derivative (Schadtet al., 1993,Jpn J. appl. Phys.,31, 2155); homogeneous alignment is induced by the axially selective photodimerization of cinnamate groups.

ISSN:0267-8292    

DOI:10.1080/02678299608031123

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Thermal microscopy (TM), differential scanning calorimetry (DSC) and dilatometric p(t) experiments were carried out to characterize the phases and to study the nature of mesomorphic transitions in two higher homologues of terephthalylidene-bis-p-n-alkylanilines, TBnAs, namely terephthalylidene-bis-p-n-tetradecylaniline, TB14A and terephthalylidene-bis-p-hexadecylaniline, TB16A. Results infer the first order nature of the isotropic-smectic C (I-Sc) and smectic C-smectic I (Sc-SI) transitions, while the smectic I-smectic F (SI-SF) transition is found to be second order. Pretransitional effects are estimated through αeffin the vicinity of mesomorphic fluctuation dominated non-linear regions (FDNLR), of the isotropic to mesomorphic transitions in TBnA homologous compounds and the relative strength of growth of FDNLR is discussed at the SIN, SISAand SISCphase transitions.

ISSN:0267-8292    

DOI:10.1080/02678299608031124

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Esterification of 2.2′-bipyridine-5,5′- and 4,4′-dicarboxylic acids with 4-alkoxyphenols leads to new mesomorphic bipyridine esters which are subsequently complexed with various metals. The synthesis and properties of these compounds are discussed.

ISSN:0267-8292    

DOI:10.1080/02678299608031125

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor