摘要:

The octadecanoate of N(-(4-hexyloxyphenyl)salicylaldimine and the corresponding Cu(II), Pd(II) and VO(IV) complexes were synthesized and studied. The compounds were characterized by IR, 1H NMR, elemental and thermal analysis and polarized light microscopy. Thermogravimetric analysis and electronic spectra of the complexes are reported. Electron paramagnetic resonance (EPR) measurements were performed.

ISSN:0267-8292    

DOI:10.1080/026782998206362

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The preparation and phase properties of some LC pi-allyl and pi-crotyl Pd(II) side group metallorganic polymers and some related salicylaldiminates are described. The LC acrylate functionalized monomers are easily prepared, but their use to obtain the corresponding polymers by radical reaction failed because extensive decomposition of the complexes occurs with the formation of Pd metal. The synthesis of the metallated polymers was therefore performed by reacting the dimeric chloro-bridged organometallic pi-allyl or pi-crotyl Pd(II) complexes with the appropriate ligand polymer which is prepared without difficulties. The organometallic polymers show a nematic mesophase, while the ligand polymer exhibits a smectic A or C phase. Both metallated low molecular mass model compounds and the polymers give stable mesophases, although at lower temperatures compared with the parent ligand compounds.

ISSN:0267-8292    

DOI:10.1080/026782998206371

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Perfluoroalkyl-substituted benzothiazolyl bisazo dyes showed higher solubility and greater bathochromicity than the corresponding alkyl derivatives. These dyes showed good dichroism (order parameter S>0.75).

ISSN:0267-8292    

DOI:10.1080/026782998206380

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Wide band dielectric and electro-optic spectroscopy of an antiferroelectric liquid crystal (AFLC) has been carried out over a range of frequencies from 1 kHz to 1 GHz. The AFLC sample under investigation possesses a variety of different ferri-, ferro-, and antiferro-electric phases. Dielectric spectroscopy of the LC cells in the antiferroelectric phases reveals both collective and individual dynamics of molecules. In the antiferroelectric SmCA phase, three dielectric relaxation processes are found in the absence of the bias and an additional relaxation process appears under the bias field. A solution of the dynamical equation of the director subject to a weak alternating field for the anitferroelectric helix has been found. A comparison of the results of electro-optic and dielectric spectroscopy with a theoretical study enables a determination of the origin of the relaxation processes in antiferroelectric phases. The mechanism for the distortion of the antiferroelectric helix has been determined using dielectric spectroscopy and a non-linear electro-optic technique.

ISSN:0267-8292    

DOI:10.1080/026782998206399

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Dielectric relaxation studies have been performed on trans -4- n -octyl-(4-cyanophenyl)is cyclohexane (8PCH) at ambient and high pressure (0.1-175MPa). Two experimental set-ups were applied: a time domain spectrometer (TDS) covering the frequency range 10 MHz-5 GHz, was used to study the relaxation processes in the isotropic phase (at ambient pressure); an impedance analyser (1 kHz-13MHz) was used for high pressure measurements on both the nematic (N) and isotropic (I) phases. The low frequency (l.f.) relaxation process connected with molecular rotations about the short axis is hindered by the activation enthalpy of 70 kJ mol-1 and 32.6kJ mol-1 in the N and I phases, respectively, whereas the high frequency process (rotations about the long axis) has an activation enthalpy of 22.6kJ mol-1 (isotropic phase). From the pressure and temperature dependencies of the l.f. relaxation time tau, the activation volume, enthalpy and energy were calculated. It was found that the energy barrier hindering the molecular rotations around the short axis in the nematic phase is influenced to about one half by the volume effects. The nematic potential q was estimated at various pressures and comprises 10 20% of the total energy barrier. The pressure dependence of q enabled the calculation of the order parameter S (p) with the aid of old (Maier and Saupe) as well as recent (Coffey et al.) theoretical formulae.

ISSN:0267-8292    

DOI:10.1080/026782998206407

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The mesomorphic phase transitions have been studied for a series of 2-(4-alkoxybiphenyl-4-yl)5-(4-methylphenyl)pyridines (4R-Pn; the carbon number, n, of the alkoxy group is 1-10) by use of DSC and polarizing optical microscopy. The 4R-Pn compounds showed only a nematic phase for n=1 and 2, but underwent characteristic polymesomorphic sequences when n>3; Cr CrH SmF SmC SmA N I with n=3 and 4, and Cr CrH SmF SmA N I with n=5-10. This mesomorphic phase transition behaviour was similar to that of the 2-(4-alkoxyphenyl)-5-(4-methylphenyl)pyridine (3R-Pn) series reported previously and it is proposed that the 4R-Pn and 3R-Pn compounds have a minimum terminal alkoxy length (critical alkoxy length) for the generation of LC polymorphism.

ISSN:0267-8292    

DOI:10.1080/026782998206416

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Long chain potassium dialkylphosphate salts, from dioctyl to dioctadecyl, were synthesized and their thermal stability was checked by thermogravimetry. Their thermotropic liquid crystalline behaviour was investigated using differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Crystalline at room temperature, they were all found to exhibit upon heating a Ia3d body-centred cubic phase followed by a columnar mesophase of hexagonal symmetry. Structures and structural parameters are discussed.

ISSN:0267-8292    

DOI:10.1080/026782998206425

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Novel mesogenic supramolecules have been constructed from the 2 :1 molar ratio of trans 4-alkoxy-4-stilbazoles CnPS (1) complexed with 2,5-thiophenedicarboxylic acid THDA (4) to form the kinked hydrogen-bonded (H-bonded) complexes (CnPS)-THDA. The analogous H-bonded complexes (CnPP)2-THDA consisting of the 2:1 molar ratio of 4-alkoxypyridines CnPP (2) and THDA (4) are also compared. In contrast to linear complexes (CnPS)2-TA prepared from the 2 :1 molar ratio of CnPS (1) and terephthalic acid TA (5), supramolecular liquid crystals with kinked molecular structures (CnPS)2-THDA are generated by introducing the thiophene unit into the H-bonded complexes. In addition, the chiral complex (C5*PS)2-THDA composed of an optically active proton acceptor (S)-(-)-4-(2-methylbutoxy)-4-stilbazole C5*PS (3) and THDA (4) (2 :1 molar ratio) is reported. Significantly, the first thiophene based supramolecular liquid crystals have been constructed in this study, and the mesogenic properties of the supramolecules can be easily adjusted not only by the nonlinear shape of the thiophene unit but also by the dipole moment derived from the lone-pair electrons of the sulphur hetero-atom.

ISSN:0267-8292    

DOI:10.1080/026782998206434

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor