摘要:

Liquid crystalline properties of 1 - (4′ - alkoxyphenylamino) - 3 - (4′ - hexyloxyphenyl)-prop-1-en-3-ones, from methoxy to heptadecyloxy, have been examined by optical, DSC, and X-ray methods. The phase diagram for the series exhibits a rich polymorphism of tilted smectic phases, for example, five mesophases were found for the hexyloxy derivative. A characteristic feature of the phase diagram is a gap in the crystal G phase area. For the heptyloxy homologue, a direct crystal H-smectic F phase transition was found; in the case of shorter as well as longer terminal substituents, the phase sequence crystal H–crystal G–smectic F is observed. Calorimetric and X-ray studies revealed the existence of a tricritical point on the crystal G–smectic F transition line.

ISSN:0267-8292    

DOI:10.1080/02678299308027719

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The mesophase behaviour of a number of non-peripherally octa-substituted phthalocyanine derivatives has been studied by optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction. A homologous series of straight chain alkoxymethyl derivatives has exhibited both rectangular and hexagonal columnar mesophases, with the rectangular phases being favoured by the shorter chains. Two branched chain derivatives were found to give rectangular columnar phases at room temperature. A detailed analysis of the X-ray data has shown some differences from the analogousn-alkyl compounds. It has been deduced that the increased polarizability and flexibility of the ether linkage allows the disc-like molecules to approach more closely face to face with correspondingly thicker columns.

ISSN:0267-8292    

DOI:10.1080/02678299308027720

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The synthesis of 4-(2′-methylbutyl)phenyl4′n-heptylbiphenyl-4-carboxylate-d18(7BEF5-d18) is presented. The compound is intended to be used as a means of studying the collective modes of liquid crystals by the coherent inelastic neutron scattering technique. The 4′-n-heptylbiphenyl-4-carboxylic acid-d12, a liquid crystalline intermediate was prepared as well; its acid chloride was coupled with 4-(2′-methylbutyl)phenol-d6to obtain the final product. The intermediates and final products were investigated by spectroscopic methods.

ISSN:0267-8292    

DOI:10.1080/02678299308027721

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Reentrant solitons are predicted to exist in homeotropic nematic liquid crystals under simple shear or in Poiseuille flow. The director equation of motion with the boundary effects due to the cell walls fully incorporated is given, which is then approximated and reduced to an effective equation of one spatial dimension with only two dimensionless parameters β and γ. For β fixed within a narrow range, as γ is varied a sequence of soliton-no soliton-soliton is obtained. This new reentrant soliton phenomenon is accessible to experimental verification.

ISSN:0267-8292    

DOI:10.1080/02678299308027722

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We have performed a structural study of the liquid crystal (LC) octylcyanobiphenyl (8CB), deposited on gratings and flat surfaces, using high resolution X-ray scattering as a function of film thickness. 8CB is a room temperature smectic A2, with a layer spacing of 31·6 Å. Glass was used as substrate and treated with either one of the organic surfactants MAP or DMOAP. Surface tension forces cause the liquid crystal molecules to align perpendicularly with respect to the plane of the substrate at the air interface. Competing with the LC-air interface, which is a strong aligner, a grating at the LC-substrate interface produces distortions in the smectic layering with an excess of elastic energy, which favours alignment parallel to the substrate and the grooves. Our purpose was to detect the onset and evolution of parallel alignment as a function of film thickness. The studies used 9 keV (1·403 Å) X-rays focused to a spot size of 2 mm2at the sample position. In-plane scans, which detect the smectic layers perpendicular to the plane of the substrate, were done at angles φ = 0° and 90° with respect to the gratings to ascertain the molecular orientation, at a nominal X-ray incidence angle of α = 0°. In order to observe regions of varying smectic layer orientation within the film, we performed a series of scans where the out-of-plane tilt angle χ changed from 0°, corresponding to scattering in the plane of the film, to 90°, which corresponds to scattering normal to the surface of the film. The results from these scans were fitted to a multilayer model where the orientation of the smectic layers varies as a function of film depth. The analysis confirmed our earlier observations that surface tension at the air interface plays a dominant role in the alignment of the LC molecules.

ISSN:0267-8292    

DOI:10.1080/02678299308027723

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Recently, we have observed dramatic changes in the electro-optic properties of PDLC films composed of droplets of the liquid crystal E7 in a matrix of polyvinylformal (PVFM) in the vicinity of the glass transition temperature of the matrix. One plausible explanation for these changes is a decrease in the surface anchoring strength on passing through the glass transition. For this reason, we undertook a study of the surface anchoring strength between E7 and a thin film of PVFM using the technique of Yokoyama and van Sprang. To mimic the properties of the matrix more closely, we dissolved 20 per cent E7 liquid crystal into the PVFM film. The surface anchoring for this film was compared with that of a pure PVFM film. From these data, we observed no obvious changes in the surface anchoring on passing through the glass transition of the matrix. However, the incorporation of liquid crystal into the matrix did cause a decrease in the surface anchoring strength. We discuss the impact of these results on the interpretation of the PDLC electro-optic properties.

ISSN:0267-8292    

DOI:10.1080/02678299308027724

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The solid state polymorphism of liquid crystalline MBBA was investigated by temperature dependent NMR spin-lattice relaxation time measurements. The sensitivity of the method could be utilized because the correlation time of the measurement is in the correlation time region of molecular motion. Motional correlation time and activation energy values were determined and the results show some interesting changes between the different solid phases. Non-trivial variation in the end-chain rotational motion in two crystalline phases has been observed. Conclusions were drawn on the relationship between rotational molecular dynamics, intermolecular order and phase transitions.

ISSN:0267-8292    

DOI:10.1080/02678299308027725

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Radial hydrodynamic flows in free suspended films (with thicknessh≥ 20 μm) of some liquid crystal materials was observed in a narrow temperature range before the line nematic-smectic C transition. The observed flows are explained by a non-linear temperature dependence of the surface tension (Marangoni effect).

ISSN:0267-8292    

DOI:10.1080/02678299308027726

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The continuum equations of Leslieet al.[1] for smectic C, and the extension of this theory for chiral smectic C* [2], are applied to problems involving simple planar layer configurations which accommodate uniform layer thickness constraints. The chiral smectic C*Mand non-chiral smectic CM[3] are considered as either biaxial smectic A phases or antiferroelectric smectic C phases and are therefore included as interesting degenerate cases of the smectic C* and C phases, respectively. The effects of static and time dependent magnetic fields on these materials are compared with related deformations occurring in nematics [4] and cholesterics [5,6]. Their reaction to applied shears is also investigated yielding examples of flow alignment, induced secondary flows and unwinding of the chiral helix and testing the validity of enforcing a constant layer thickness.

ISSN:0267-8292    

DOI:10.1080/02678299308027727

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Biphasic blends (mixtures) of liquid crystal ionomers (prepared from ferrocene containing liquid crystal polymers by a redox reaction) and partially sulfonated polystyrene combine the constituent properties in a way, which is dependent on the measuring method. Polarizing microscopy shows homogenous textures similar to the pure liquid crystal polymer. Mechanical measurements show however the elastomeric behaviour of sulfonated polystyrene. The phase separated structure of these blends is proved by differential scanning calorimetry measurements.

ISSN:0267-8292    

DOI:10.1080/02678299308027728

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor