摘要:

The In-Plane Switching (IPS) mode of liquid crystal displays (LCDs) has a wide viewing angle compared with the conventional 90°-TN mode, but requires a higher driving voltage to reach a maximum transmittance. The electro-optical properties of IPS mode LC cells were analyzed by the LC continuum theory to achieve a maximum transmittance with unnoticeable spectra dispersion at low operating voltages.

ISSN:1058-725X    

DOI:10.1080/10587259808042426

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Suitably deposited thin films of poly (tetrafluoroethylene) (PTFE) will induce alignment in a liquid crystal [1]. These films are deposited in a one step dry process which offers advantages over polyimide or SiO2alignment layer application [2]. Previous studies of such films [3, 4] have shown the quality of liquid crystal alignment to be good and to exhibit an induced surface pretilt of the order of 1°. The relationship between the conditions under which the films are deposited, the uniformity of the deposited film and the induced surface pretilt induced by these surfaces has been investigated further. The uniformity has been studied by observation of the surface tension and the pretilt studied using a modified version of the crystal rotation method. There would appear to be a relationship between the observed uniformity of the surface, the alignment quality and the induced pretilt observed. The data are consistent with the hypothesis that the induced surface pretilt observed is due to irregularities in the structure of the surface.

ISSN:1058-725X    

DOI:10.1080/10587259808042427

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A homologous series ofN-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-cyanoanilines [AHC(n;n= 1–8, 10, 12)] was synthesized. AHC(4–8, 10) exhibit a monotropic nematic phase. The temperature dependence of infrared (IR) spectra of AHC(4–8) has been observed in the spectral range of 2300–600cm−1. On cooling, the intensity of the IR band at 2230cm−1remained unchanged through the phase-transition of isotropic-nematic and increased gradually toward room temperature (solid phase). This band can be assigned to the C ≡ N stretching vibrational mode. The wavenumber of the band increased slightly (about 1 cm−1) during the temperature from isotropic to solid. Inmela-CN substituted AHC, it is suggested that the CN group may not play a dominant role in the intermolecular interaction.

ISSN:1058-725X    

DOI:10.1080/10587259808042428

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Photochemical phase transition behavior of polymer azobenzene liquid crystals (LCs) was explored by transmission-mode analysis and reflection-mode analysis. Four samples with different structures were used, which show LC behavior in thetransform but no LC phase in thecisisomer. Attention was focused on the effect of the position of the mesogenic azobenzene moiety in the flexible side chain on the photochemical phase transition behavior. Photoirradiation of a thin film of the azobenzene LCs (∼200 nm) in thetransform resulted in the disappearance of the LC phase due totrans-cisphotoisomerization of each mesogen. and the LC phase recovered quickly when the irradiated sample was kept in the dark because of thermalcis-transback-isomerization. In all polymers, the photochemical LC to isotropic (I) phase transition was induced in 100∼200 us on laser pulse irradiation. In the sample with an azobenzene located apart from the main chain of the polymer by a spacer, the LC-I phase transition took place almost completely. In the sample with the azobenzene moiety in the vicinity of the main chain, however, the photochemical phase transition was induced only locally. These phenomena are interpreted in terms of the mobility of the azobenzene moiety in the side chain and the stability of the LC phase.

ISSN:1058-725X    

DOI:10.1080/10587259808042429

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Further X-ray powder diffractometer measurements have been made on compound II-9 of the columnar liquid crystal series hexaalkanoyloxytribenzocyclononene. For this compound the transition temperature between the solid and the columnar phase is 26°C. Data have been collected at several temperatures from 2°C to 52°C. We compare results obtained from II-9 with results published for II-10, 12, 13 and 15. Unlike these other compounds, in the mesophase the diffraction patterns show a large number of lines, with at least four high angle lines superposed on the broad hump arising from scattering by the disordered hydrocarbon side chains. This indicates a more highly ordered structure than for the other compounds in this series.

ISSN:1058-725X    

DOI:10.1080/10587259808042430

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The esters of 2,5-bis(2-carboxy-phenylthio)terephthalic acid4a-f were prepared by reaction of 2,5-bis(2-carboxy-phenylthio)terephthalic acid2viachloride 3 with alcohols or phenols. These novel glass-forming compounds are of the sulfur ligated “trilling” type. Two structures were established by X-ray analysis as well. The thermal behavior was characterized by DSC. In dependence of the different lateral substituents we found calorimetric glass transition temperatures (Tg) in the range of −50°C to 85°C. The molecular dynamics were investigated by use of dielectric spectroscopy (10-2Hz-109Hz). The temperature time dependence for the α-relaxation, which is associated with the glass transition, is discussed in the fragility concept of liquids.

ISSN:1058-725X    

DOI:10.1080/10587259808042431

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Total internal reflection (TIR) Raman scattering spectroscopy was performed using a cell combined with a high index hemicylindrical substrate and a glass plate with obliquely evaporated SiO alignment layers to study an electric-field-induced reorientation process of 4-n-hexyl-4′-cyanobiphenyl (6CB) in a nematic phase. Two types of cells having different director configurations were studied; one has the orientation of the director parallel to the axis of the hemicylinder (s-configuration) and the other the director perpendicular to the axis (p-configuration). Squared relative Raman scattering tensor components of the LC layer were determined by analyzing the polarized TIR Raman spectra observed for the cells. Time-resolved TIR Raman measurements were performed on thep-configuration cell under application of squared electric fields (duration = 10 ms, repetition rate = 10 and 5 Hz, amplitude = 3–8 V) by using a pulsed Nd-YAG laser (Λex= 532 nm, pulse width = about 15 ns). The results elucidated characteristics of the electric field-induced reorientation dynamics of a layer of the LC molecules (with a thickness of about 50 nm) adsorbed on the evaporated SiO film: (i) Upon application of the electric field with the amplitudes of 3–5 V the director of the surface layer keeps its original orientation for a certain period, although the director of the bulk phase immediately responds to the fields; the period becomes longer as the amplitude decreases, being ca. 4 ms for the amplitude of 5 V and about 6 ms for 3 V: (ii) After switching off the electric fields the surface layer exhibits a rapid recovery process with the time constant for 3–6 ms, which is appreciably shorter than that of the bulk phase of almost 350 ms (measured under application of the squared electric field of 9 V). An elastic interaction force within the former

ISSN:1058-725X    

DOI:10.1080/10587259808042432

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In the previous paper [2], we studied the effect of a hybrid tail on theS*cphase range of a three-ring core mesogen. It is concluded that the ether tail has a small number of contorted, but energetically favored conformers. The hybrid tail has a slightly contorted minimum energy conformation but the fluorine substituents have raised the energy of the particular deep levels available to the ether tail. In brief, the ether substituents enable gauche conformers, and the fluorine substituent prevent the gauche conformers from becoming overwhelming. In an extension to further demonstrate the validity of our theory, we have examined the effect of a butoxyethoxyethoxy tail (BO tail). It is expected that this tail should display a significant effect on the smectic mesophase, especially theS*cphase because the rigidity of the tail increases with the extension of terminal carbon chain from two to four.

ISSN:1058-725X    

DOI:10.1080/10587259808042433

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

According to the temperature-composition phase diagram of Cetyltrimethylammonium chloride (CTAC) andp-phenylphenol (p-PP), which was obtained by DTA measurement of powder mixtures at various composition ratios, it was found that only one complex with a 1/1 molar ratio was available for the CTAC/p-PP system. The single crystal structure of this complex, together with the crystal structure of CTAC, was determined by the X-ray diffraction method. Both crystals have a smectic layer structure stacked along thec-axis. The CTAC (andp-PP) molecules are arranged almost perpendicular to the layer surface. Within the smectic layer of the host (CTAC) crystal, long alkyl chains from both sides of layer surfaces are interdigitated mutually, which makes a hydrophobic region in the middle of the layer. In complex (CTAC/p-PP) crystals, guest (p-PP) molecules were accommodated in the space formed by loosening their interdigitation. The arrangement ofp-PP molecules found in the complex crystal is very similar to that in thep-PP crystal. The thermal behavior of complex crystals is also very similar to that ofp-PP. Therefore, the complex structure seemed to be highly influenced by the guest-guest interaction. We call this type of complex structure a “guest-dependent” structure.

ISSN:1058-725X    

DOI:10.1080/10587259808042434

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A simple mean field theory is introduced to describe volume phase transitions of gels dissolved in a liquid crystal solvent. We predict that the gel shows the second-order volume phase transition at the nematic-isotropic transition temperatureT°NIof the pure liquid crystals existing outside of the gel. BelowT°NI, the gel is condensed due to the nematic ordering of the pure liquid crystals. We also find the first-order volume phase transition in the isotropic phase aboveT°NI.

ISSN:1058-725X    

DOI:10.1080/10587259808042435

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor