摘要:

The change in backbone conformation from prolate to oblate upon going from the re-entrant nematic to the smectic Adphase is studied in a comb-shaped polyacrylate by measuring the mosaicity of the sample in the smectic phase with X-ray scattering. In combination with the possibility of aligning the director in both nematic phases, the results indicate that the conformational change takes place in the re-entrant nematic phase upon approaching the smectic Adphase.

ISSN:0267-8292    

DOI:10.1080/02678299408027855

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A convenient NMR method for the determination of the order parameters for liquid crystals containing a fluorinated phenyl ring is described. The technique consists of measuring the carbon-fluorine dipolar coupling constants in the one-dimensional C-13 spectrum of the molecule. The order parameters may then be calculated for the fluorine-containing ring with a high degree of precision because of the excellent resolution afforded by the 1-D C-13 spectra. The method is used to determine the core order parameters for 4-n-hexyloxybenzilidene-4′-fluoroaniline (FAB-OC6). The results of the carbon-fluorine dipolar coupling method are compared with two established methods for determining the core order parameters of phenyl rings, namely deuterium NMR spectroscopy and SLF/VAS, a two-dimensional C-13 NMR spectroscopy. Some comments about the orientational properties of the fluorinated liquid crystal FAB-OC6 are made.

ISSN:0267-8292    

DOI:10.1080/02678299408027856

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

X-ray reflectivity studies on Langmuir-Blodgett multilayer films of side-chain liquid crystal polymers are reported. The films have a high degree of lamellar order. The layer periodicity is independent of the type of monolayer deposition, implying a reorientation of the side group mesogens following the deposition process. X-ray reflectivity from thin films displays subsidiary maxima permitting a quantitative measure of the change in side-chain density between multilayer and monolayer. A unit cell density profile is calculated for thick films assuming a symmetric unit cell.

ISSN:0267-8292    

DOI:10.1080/02678299408027857

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Quantitative investigations ofE,Z-photoisomerization of chiral dopants (−)-2-arylidene-p-menthanones were carried out using solvents of different nature and various liquid crystalline matrices.

ISSN:0267-8292    

DOI:10.1080/02678299408027858

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We present the results of our studies of the ferroelectric properties of mixtures of a high polarization, ferroelectric liquid crystalline copolymer and its side-group antecedent, a high polarization, low molecular weight, ferroelectric mesogen. These two materials are found to be completely miscible in all proportions. Spontaneous polarization values and electro-optical response times are found to be monotonic functions of the weight percentage of the mesogen in the mixture, while optical tilt angles do not exhibit such a monotonic dependence.

ISSN:0267-8292    

DOI:10.1080/02678299408027859

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We have measured self-diffusion coefficients of amphiphile and water molecules in novel inverse micellar lyotropic cubic phases using the pulsed field gradient NMR technique. We investigated two different ternary lyotropic systems: oleic acid/sodium oleate/water, and dioleoylglycerol/dioleoylphosphatidylcholine/water. Both of these systems have previously been shown by one of us to form a cubic phase of space group Fd3m, whose structure is a complex packing of two types of disconnected quasi-spherical inverse micelles embedded in a 3D hydrocarbon matrix. The amphiphile translational diffusion coefficients determined for the first time by1H NMR in both systems are surprisingly large. Thus the self diffusion coefficients of amphiphiles may not provide a reliable way of distinguising inverse micellar from inverse bicontinuous phases. The water self-diffusion coefficient has been determined to have a value of 2·4 × 10−12m2s−1, a value which is more than two orders of magnitude lower than that typically observed for inverse bicontinuous cubic phases. This confirms unambiguously the inverse micellar topology of the Fd3m cubic phase, and indicates that the value of the water diffusion coefficient should permit inverse micellar and inverse bicontinuous structures to be reliably distinguished, even for systems where the structure has not been previously determined by diffraction.

ISSN:0267-8292    

DOI:10.1080/02678299408027860

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Vanadium pentoxide gels and sols, V2O5,nH2O, exhibit a ribbon-like structure. They form colloidal suspensions (also called Zocher phases or ‘tactophases’) which are clearly shown here to present a homogeneous lyotropic nematic phase for concentrations larger than ≈0·12mol 1−1. Classical threaded textures were observed in polarized light and small angle X-ray scattering patterns of oriented samples displayed a diffuse spot quite comparable to that of the Tobacco Mosaic Virus. For a sample of volume fraction φ ≈ 5 per cent, the V2O5ribbons are separated by about 160 Å, so that the cross sectional area of the ribbons is about 1300 Å2, in agreement with previous estimations by electron microscopy.

ISSN:0267-8292    

DOI:10.1080/02678299408027861

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0267-8292    

DOI:10.1080/02678299408027844

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor