摘要:

We herein report an efficient synthesis of 1,2,3,5,6,7-hexaalkoxy-9,10-anthraquinones (also called rufigallol hexaethers) starting from gallic acid. These ethers are known to form columnar phases which are suitable for the study of charge transport, photoconductivity etc. Our X-ray diffraction studies show that the high-temperature mesophase is hexagonal columnar with correlation among the molecular cores along the column (Colh, also called Dh), and that, identified for the first time in these systems, there are one or two additional mesophases at low temperature depending on the system, some of them three-dimensionally ordered. Our results show that the mesophase (high-temperature) range does not dramatically decrease as the length of the alkyl chains at the 1,5 positions become longer than the rest. Since these molecules have absorption in the visible region they may also be the potential candidates for studying photovoltaic effects that are of interest in developing energy conversion applications.

ISSN:1058-725X    

DOI:10.1080/10587250008025228

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A few new metallomesogens contaning Ni(II) and Cu(II) atoms of the ligands 4-substituted 2′-hydroxy 4′(4″-n-hexadecyloxybenzoloxy)azobenzenes have been synthesized. The complexes have been characterized by C, H, N, microanalysis, IR, NMR and UV-Visible spectroscopies. Mesomorphic properties of all the ligands and complexes were investigated on a Leitz Laborlux 12 POL microscope provided with a heating stage.

ISSN:1058-725X    

DOI:10.1080/10587250008025229

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We report on electrooptic measurements on Langmuir-Blodgett (LB) monolayers of a 1/1 mixture of n-octyl-cyanobiphenyl (8CB) and stearic acid. The required sensitivity is achieved by depositing the LB-film on a thin gold layer and measuring the field-induced shift of the surface plasmon resonance. The existence of a finite electrooptic coefficient is proof of polar anisotropy in the monolayer. The electrooptic coefficient depends on details of the deposition process and does not change with temperature or frequency of the applied electric field.

ISSN:1058-725X    

DOI:10.1080/10587250008025230

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The study on the wetting properties of a liquid crystal (LC) on two types of polyimide (PI) films has been done for clarifying the azimuthal surface anchoring properties of LC adsorbed on the films. The results show that the PI showing high wettability of a LC phase gives a higher azimuthal anchoring energy and less temperature dependence of the anchoring energy than the PI with low wettability. We also show that long exposure of a LC phase to PI surfaces leads to a strong adsorption state of LC molecules, indicating the importance of the wetting properties to realize thermal-stable (strong azimuthal anchoring) surface LC alignment.

ISSN:1058-725X    

DOI:10.1080/10587250008025231

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Some new 9,10-anthraquinone (rufigallol) derivatives have been prepared and their mesomorphic properties have been studied. The unsymmetrically substituted tetrahydropyranyloxy-ethers (THP-ethers), exhibited columnar mesomorphism at fairly low temperatures and the xray studies carried out for one of the homologues confirmed the hexagonal nature of the mesophase. The deprotected derivatives of these THP-ethers, also form columnar mesophases. All these derivatives are very good candidates for polymerisation studies.

ISSN:1058-725X    

DOI:10.1080/10587250008025232

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

On the basis of the concept used in the high-electric-field method reported by Yokoyama, we have developed a new measurement method of the polar anchoring energy of nematic liquid crystals. This method can derive the polar anchoring energy only by measuring the capacitance change against the applied voltage of a LC sample, and thus the method can be easily applied to measuring the polar anchoring energy of homeotropically-aligned samples. This paper presents the results of the computer simulation for verifying the developed method and also some experimental results of the polar anchoring energy for homeotropically-aligned samples.

ISSN:1058-725X    

DOI:10.1080/10587250008025233

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Materials composed of photoactive molecules like azobenzenes are known to show photo-induced isothermal phase transitions. However, in all the cases investigated so far, the trans-cis conversion brought about by photoisomerization always leads to an order to disorder transition, i.e., the ordering decreases in the process. In this paper we report observation of the reverse behavior, namely, a photo-induced disorder to order transition. Experiments have been done on a binary liquid crystalline system doped with a photoactive azo molecule, showing a reentrant nematic-smectic A phase transition. In the reentrant nematic phase UV illumination of the sample and the consequent photoisomerization leads to the transformation to the smectic A phase. A possible explanation for this behavior is suggested on the basis of the recently proposed photo controlled nanophase segregation mechanism.

ISSN:1058-725X    

DOI:10.1080/10587250008025234

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

4,4′-Bis[4-(4-alkoxybenzylideneamino)benzoyloxy]diphenylmethanes bearing methoxy to decyoxy groups exhibit a smectic C phase. Compared with the behavior of the isomeric 4,4′-bis [4-(4-alkoxybenzoyloxy)benzylideneamino]diphenylmethane, the clearing point tends to be higher though falls more rapidly by the increase of the alkyl chain length and the melting point tends to be lower, resulting in the mesophase temperature range wider by a factor of two or more for most of the homologous members. 4,4′-Bis[4-(4-alkxoybenzoyloxy)benzylideneamino]diphenylamines are nematogenic and smectic A and B phases are additionally observed for the heptyloxy and octyloxy members.

ISSN:1058-725X    

DOI:10.1080/10587250008025235

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Two monosubstituted ferrocene derivatives, 8-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyl]octyl 4-ferrocenylbenzoate (MPAF-8) and 9-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyl] nonyl 4-ferrocenylbenzoate (MPAF-9), were synthesized and their phase transition behavior was studied using a differential scanning calorimeter, a polarizing microscope and an X-ray diffractometer. MPAF-8 exhibited two liquid crystalline phases in both heating and cooling processes at approximately room temperature. In the heating process, a crystal-crystal phase transition behavior was ascertained. The phase transition behavior of MPAF-9 was very similar to that of MPAF-8 except for the behavior of the crystal-crystal phase transition in the heating process. In MPAF-8, one crystalline phase was transformed into another crystalline phase completely. On the other hand, this transformation was observed in part in MPAF-9, and as a result, the melting behavior was observed two times in the heating process.

ISSN:1058-725X    

DOI:10.1080/10587250008025236

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Dynamic mechanical and stress-optical measurements on nematic liquid single elastomers have been carried out both in the nematic and in the isotropic phase. In case of shear stress and in case of tensile stress applied parallel to the director the compliances were not affected by the nematic-isotropic transition. For tensile stress oriented perpendicular an increased compliance was observed in the vicinity of the phase transition. The stress-optical coefficients for tensile stresses applied pararallel and perpendicular to the director both increase on approaching the nematic-isotropic transition. In the isotropic phase its temperature dependence is well described by the Landau-de Gennes theory. Far from the transition temperature in the nematic phase other mechanisms superpose this behavior, leading to negative stress-optical coeffients for stress parallel, and positive coefficients perpendicular to the director.

ISSN:1058-725X    

DOI:10.1080/10587250008025237

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor