摘要:

The mesomorphic behaviour of a liquid crystalline sheet-shaped 2,4,6-triarylaminothe 1,3,5-triazine bearing six peripheral decyloxy chains has been investigated in binary mixtures with two-fold alkoxy substituted non-mesomorphic benzoic acids. Each investigated equimolar mixture exhibits an enantiotropic columnar phase with either a hexagonal or a rectangular lattice. The two-dimensional lattice parameters depend on length and positions of the flexible alkoxy chains of the aromatic carboxylic acids. The structure formation of the mixed systems giving rise to variations of the mesophase structure of the pure triarylaminotriazine results from intermolecular hydrogen bonding between the complementary melamine and acid components.

ISSN:0267-8292    

DOI:10.1080/026782998207226

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Supramolecular hydrogen-bonded networks have been prepared by self-assembly of a chiral bifunctional H-bond acceptor and achiral trifunctional H-bond donors. A stilbazole dimer, (R)-1,2-bis{4-\[2-(4-pyridyl)ethenyl]phenoxy}propane (1) has been synthesized for use as a chiral component for cholesteric networks. Compound 1 has been complexed with tri functional H-bond donors, p,q-bis{2-\[2-(4-carboxyphenoxy)ethoxy]ethoxy}benzoic(2-6) \[p, q =2,4 (2); 2,5 (3); 2,6 (4); 3,4 (5); 3,5 (6)], maintaining the 1 :1 donor/acceptor group stoichiometry. With the exception of the complex from 1 and 6, these H-bonded complexes exhibit cholesteric phases and glass transition behaviour, while all individual components are non-mesomorphic. For example, the H-bonded complex consisting of 1 and 2 shows a cholesteric phase from 75 to 184 C on heating. These results suggest that supramolecular liquid crystalline networks with macroscopic helical structures have been formed by intermolecular hydrogen bonds between non-mesomorphic smaller molecules. The solid state films obtained by cooling the samples from their mesophases exhibit cholesteric colours associated with selective reflection. The cholesteric structure is preserved in the glassy state of the networks.

ISSN:0267-8292    

DOI:10.1080/026782998207235

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The core structure of a disclination line of strength 1 in uniaxial nematics is determined by using a space-dependent mean-field approach somehow based on the rod-like molecular model. It is shown that, due to distortion, biaxiality arises at all points of the defect core, except at the centre line where symmetry dictates uniaxiality; the orientational distribution of the rod-like molecules is there 'oblate', however. Although, as is well known, the configuration of a 1 defect is stable only under limiting conditions (as compared with either escaping in the axial direction or splitting into two 1/2 lines), the simple example developed here is indicative of a method which can readily be extended to more realistic, if mathematically more complex, situations such as 1/2 lines, layers close to solid boundaries, etc.

ISSN:0267-8292    

DOI:10.1080/026782998207244

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Mono-layers of stearic and behenic acids, deposited with the Langmuir-Blodgett technique, were used as aligning films in nematic liquid crystal cells. During the filling process the liquid crystal adopts a deformed quasi-planar alignment with splay-bend deformation and preferred orientation along the filling direction. This state is metastable and transforms with time into a homeotropic state once the flow has ceased. The transition is accompanied by formation of disclination lines which nucleate at the edges of the cell. The lifetime of the metastable splay-bend state was found to depend on the cell thickness. On heating, an anchoring transition from quasi-homeotropic to degenerate tilted alignment in the form of circular domains takes place near the transition to the isotropic phase. The anchoring transition is reversible with a small hysteresis.

ISSN:0267-8292    

DOI:10.1080/026782998207253

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new reflective liquid crystal display, the sub-twisted nematic LCD (SBTN), is presented. The SBTN, specifically designed for its twist angle, the product of cell thickness and birefringence, the direction of its only polarizer, etc. exhibits good electro-optic performance. Brightness, contrast, colour dispersion and multiplexing ability, etc. were theoretically and experimentally examined. The prototype showed high brightness, little dispersion, good mutliplexing ability, good viewing angle and response behaviour. It also offers good manufacturing tolerance and low production cost.

ISSN:0267-8292    

DOI:10.1080/026782998207262

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

With the laser intensity modulation method (LIMM), polarization and charge profiles in sandwich cells containing the ferroelectric liquid crystal side group polymer LCP1 have been investigated. In a sample with a thickness larger than the helical pitch, contributions to the polarization profile due to surface anchoring were found. Additional contributions inside the cell occurred. The validity of the results, concerning numerical deviations in the deconvolution process of the pyrospectra, has been tested by simulations. The influence of space charges for measurements with a static external electrical field is discussed, giving contributions to the profile in addition to those arising from polarization.

ISSN:0267-8292    

DOI:10.1080/026782998207271

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The dij coefficients of the second-order susceptibility tensor for second harmonic generation were detemined for a calamitic ferroelectric liquid crystal (FLC) specifically designed for applications in non-linear optics. The measurements were performed at different temperatures in the SmC* phase. In accordance with the design methodology of these materials, the coefficient along the polar axis d22 is the greatest, and depicts an expected behaviour in the whole range of the ferroelectric phase. On the other hand, the temperature dependence of d21, d23, and d25, is anomalous to some extent, including a sign inversion of d23 at a certain temperature. These results, which contrast with those reported recently for non-calamitic FLCs, were qualitatively interpreted in the light of different conformations which, by virtue of plausible distortions of the molecular core, could coexist in the sample.

ISSN:0267-8292    

DOI:10.1080/026782998207280

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The phase behaviour and the structure of three poly(1,3-propylene adipate)s containing cyanoazobenzene side groups bonded to the backbone unit through flexible spacers with 6, 8 and 10 methylene groups have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis. The polyadipates behave as enantiotropic side group liquid crystalline polymers. XRD analysis has shown that the organized phase of these polyadipates possesses a crystalline or a tilted structure of the SmF or SmG type. The temperature of fusion of this phase (Tm= 45-48 C) is almost independent of the length of the side group spacers. The crystalline phase can be obtained only by prolonged annealing at room temperature because crystallization from kinetically hindered. The range of thermodynamic stability (Ti- Tm) of the mesophase formed on melting increases with the length of the side group flexible spacers. The structure of the mesophase, determined by XRD, is of the smectic A type, and is characterized by a relatively large longitudinal displacement of the side groups, which is responsible for the unusually weak low angle Bragg reflections.

ISSN:0267-8292    

DOI:10.1080/026782998207299

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Electromechanical (converse piezoelectric) responses of an electrically switchable chiral ferroelectric columnar liquid crystal 1,2,5,6,8,9,12,13-octakis\[(S)-2-heptyloxy] dibenzo\[e,l] pyrene, were studied under a.c. electric fields. The liquid crystal phase has a C2 rotational symmetry, the same as that of SmC* liquid crystals or of Rochelle Salt, but the responses are orders of magnitude weaker. The possible physical reasons for the observed weak mechanical responses and, in view of the results, the switching mechanism are discussed.

ISSN:0267-8292    

DOI:10.1080/026782998207307

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Pretilt angle generation in a nematic liquid crystal (NLC) by a transcription alignment technique, as used for non-rubbed polyimide (PI) surfaces with side chain, has been investigated. Monodomain alignment of the NLC in cells fabricated by transcription alignment on a PI surface was observed. The generated pretilt angle of the NLC is about 3.7 ; it decreases with increasing rubbing time of the original substrate. It is considered that the generation of the NLC pretilt angle may be attributed to steric interaction due to the polymer side chain. It is also suggested that the LC alignment produced by the transcription alignment technique is attributable to a memory effect of the NLC on the PI surfaces.

ISSN:0267-8292    

DOI:10.1080/026782998207316

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor