摘要:

Disorder and motion in crystals of tetra-n-alkylammonium halides of short chain length alkyl groups, [CH3(CH2)n-1]4NX, wheren =1, 2, 3 and X = Br and I, have been analyzed based on solid state NMR. The solid-mesophase phase transitions involve orientational motion and disorder of the cation as a whole, so that the mesophases must be identified as plastic crystals. Except for the methyl rotation, the conformational motion,i.e., the rotation about single-bonds, is limited to small-angle librations that do not reach other conformational isomers. The analyzed salts show, thus, a plastic-crystal me-sophase without conformational disorder. The information on the disorder and motion, obtained initially by thermal analysis of the transition, agrees well with the more detailed NMR results.

ISSN:1058-725X    

DOI:10.1080/10587259208033434

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Disorder and motion in crystals and mesophases of tetra-n-alkylammonium halides of intermediate chain length alkyl groups, [CH3(CH2)n-1]4NX, wheren= 4, 5, 6, 7 and X = Br and I, have been analyzed based on entropy changes of phase transitions known from differential scanning calorimetry (DSC) and new measurements of solid state13C nuclear magnetic resonance spectra (NMR). Some mesophase transitions from the crystal state involve only conformational motion and disordering to lead to condis crystals. The conformational motion and disordering in the alkyl chains may also be introduced gradually (transitionless change to a condis crystals). Further heating of the samples increases the degree of conformational disorder (entropy) to reach different, more disordered condis states, or causes orientational motion and disorder of the cation as a whole to form plastic crystals, which in this intermediate alkyl chain-length group of salts contain always conformational disorder. Finally, isotropization occurs either directly from the condis state or out of the plastic crystal.

ISSN:1058-725X    

DOI:10.1080/10587259208033435

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

On the basis of the bifurcational analysis it is shown that the Prost model of a frustrated smectic liquid crystal with interacting antiferroelectric and translational order parameters permits three modes of behaviour of molecular systems which correspond to three qualitatively different types of separatrices-manifolds dividing the control parameters space into open areas with topologically different structures of a thermodynamic potential. Phase diagrams of the model for each of the separatrices are built. It is established that phase diagrams with two tri-critical points on equilibrium lines similar to those described by the original Prost theory and found experimentally in mixtures of cyanobiphenyls correspond to two types of separatrices. Phase diagrams with three tri-critical points (two of which are located on the curve of coexistence of mono-and bilayer smectics and the third one occurs on the curve of co-existence of bilayer smectic and nematic mesophases) are inherent to the third type of separatrices.

ISSN:1058-725X    

DOI:10.1080/10587259208033436

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The synthesis of N,N′-disubstituted naphthyl(azo)-2,3-dihydroperimidine blue dyes and a comparison of their absorption maxima and solubility in ferroelectric liquid crystal (FLC) hosts is described. The N,N′-disubstituted azo perimidines exhibited a much higher absorption maxima (20-50 nm) than their unsubstituted counterparts. In addition, the absorption maxima of the naphthyl(azo) perimidines was significantly higher than their phenyl(azo) analogues. Although the FLC solubility of the N,N′-dimethyl substituted dyes was similar to that measured for analogous unsubstituted dyes, the N,N′-dibutyl substituted bis(azo) dyes exhibited solubilities in excess of 8%.

ISSN:1058-725X    

DOI:10.1080/10587259208033437

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The operational principle of a transflective mode quarter wave plate dichroic liquid crystal display is described. It consists of a dichroic shutter and a polarizer sandwiching two quarter wave plates, one on each side of a transflector. In transmissive mode it acts like a Heilmeier display. The cell construction is discussed and electro-optical measurements are reported. With proper dichroic mixture and cell construction, we have achieved a contrast ratio of 10:1 in reflective mode and 30:1 in transmissive mode. This display is much brighter than TN and Heilmeier mode LCDs as it does not require a polarizer in reflective mode. It also has no unwanted memory effect.

ISSN:1058-725X    

DOI:10.1080/10587259208033438

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Earlier, phase transitions of triterpene fatty acid esters were studied for a few new triterpenes in this lab. In the present investigation, synthesis of axial and equatorial fatty acid esters of a triterpene were synthesised and their liquid crystal transition temperatures were determined using a polarising microscope. The effect of equatorial and axial orientation of the ester grouping on phase transitions was highlighted.

ISSN:1058-725X    

DOI:10.1080/10587259208033439

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The title complexes containing platinum-carbon [sgrave]-bonds and triethylphosphine ligands were synthesized and their thermal properties were examined. The complexes composed of a four-ring system showed enantiotropic nematic phases, though they have a very large lateral group. Direction of the ester group of the complexes strongly influenced the thermal stability of mesophases.

ISSN:1058-725X    

DOI:10.1080/10587259208033440

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Polyindole hexafluorophosphate (PIPF6) was prepared by electrooxidation supplying a potential of 0.7 V. The cyclic voltammetry suggested that the electrode reaction was irreversible, and the electropol-ymerization of indole formed radical cations. Thermogravimetric analyses of the polyindole-based systems were performed at a temperature range of 25 ∼ 800°C under a nitrogen atmosphere. From the TGA results, we concluded that most polyindole systems mainly decomposed at higher temperatures than the polyaniline-based ones. The maximum thermal decomposition rate (Rmax) for polyindole systems was unaffected by the kind of electron acceptors, but the values of the polyaniline-based materials were affected by dopants. The electrical conductivity of the PIPF6was measured in a temperature range from-150 to 25°C. The values of log a at 25°C and of Eaas calculated from an Arrhenius plot were -4.15 S/cm and 0.64 eV, respectively. Our conductivity measurements suggest that a possible conduction mechanism for the PIPF6pellet is the hopping conduction, and that the charge carriers are polarons. The ESR analysis of the PIPF6powder was performed at 25°C, and, thus, parameters of ΔHPP, g-value and spectra ratio were obtained.

ISSN:1058-725X    

DOI:10.1080/10587259208033441

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Phase diagram, linear velocity of crystallization, thermochemistry, microstructure, electrical conductivity, X-ray diffraction and spectral behaviour of phenanthrenem nitrobenzoic acid system have been studied. The results obtained in the present investigation have been discussed in the light of recent advancement in the area of organic eutectics and molecular complexes.

ISSN:1058-725X    

DOI:10.1080/10587259208033442

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An X-ray study of the crystals of C-(2-naphthyl-1-vinyl)-N-n-methylphenyl nitrone (I) and C-(2-naphthyl-1-vinyp-N-phenyl nitrone (II) has been performed. The main crystal data of I: C20H17NO2.a= 15.937(7) Å,b =13.240(9) Å,c= 8.000(7) Å, γ = 74.3(2)0,M =303.84,V= 1688(1) Å3,dcalc= 1.195(3) g/cm3, Space gr. P21/b,Z= 4. The main crystal data of II: C19H15NO2× 1/2H2O,a= 26.428(11) Å,b= 17.504(6) Å,c= 6.657(2) Å, γ = 97.3(2)0,M= 298.02,V= 3053(1) ǎ3,dcalc= 1.296(2) g/cm3, Space gr. B2/b,Z= 8.

ISSN:1058-725X    

DOI:10.1080/10587259208033443

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor