摘要:

Two particular aspects of solute dynamics in ordered media are analysed on the basis of the solution of multivariate diffusion equations: the effects of the solvation dynamics on the rotational motions of dipolar probes in liquid crystal solvents, and the alteration of reaction pathways in isomerization kinetics caused by the solvent order. The introduction of a suitable solvent coordinate allows the interpretation of high frequency contributions in the rotational correlation functions observed by spectroscopic techniques, namely dielectric dispersion, IR and Raman spectroscopy, ESR lineshapes and optical Kerr effect. For molecular systems undergoing conformational changes, a method is offered to evaluate the modification of the torsional barriers resulting from the anisotropic torques modulated by the molecular shape changes along the reaction coordinate.

ISSN:0267-8292    

DOI:10.1080/02678299308027310

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Wave mixing due to molecular reorientation in electric field biased nematic thin films is studied. By using the continuum theory, general formulae have been derived for the orientational angle distribution. The concept of a thin film grating is utilized to describe the diffraction efficiency. Experimental results which exhibit the behaviours of the transmission beam and diffraction beams have been obtained as predicted by the numerical calculation.

ISSN:0267-8292    

DOI:10.1080/02678299308027311

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Comb-like liquid-crystalline polymers exhibit many unique properties that challenge not only basic research but also numerous technological opportunities. They combine (partly) the properties of orientation of low molecular weight liquid crystals with the rigidity of polymers. For example, they can be oriented in the mesomorphic state and the structure frozen in a glassy state. These polymers with functionalized pendent groups lead to potential applications in the field of nonlinear optics, or in the domain of electro-optical displays. Other polymers like polysilanes show interesting properties such as photo-conductivity. This paper describes the properties and applications of some new side chain liquid-crystalline polyacrylates and their amorphous copolymers. It also describes the photo-conductive properties of polysilanes and their applications in spatial light modulators with liquid crystals. In the first part of this paper, we describe the properties of liquid crystal copolymers and amorphous polyacrylate copolymers with cyanobiphenyls and/or pendent groups with a large hyperpolarizability. Their different properties are compared with some recent results from the literature. These amorphous copolymers allow one to obtain, after poling in an electric field, high optical non-linear coefficients. We have used these copolymers for the manufacture of an electro-optic modulator working at 1·3 μm in the frequency range of 1 GHz. Applications to second harmonic generation at 1·06 μm are also discussed. In the second part of this paper we describe the photo-conductive properties of polysilanes and the realization and performance of an organic spatial light modulator for optical correlation.

ISSN:0267-8292    

DOI:10.1080/02678299308027312

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Glass-forming liquid-crystalline group polymers were investigated by2H 2D exchange NMR. In oriented systems, the exchange pattern of a single 2D spectrum yields the orientational distribution function with at least as high precision as a full rotation pattern of 1D spectra. In addition, important information about the geometry of the phenyl-flip motion is obtained. The 2D lineshapes are particularly sensitive towards possible slow motion of the flip axis which could be envisaged to fluctuate within the orientational distribution of the mesogenic group. However, the experimental spectra for a frozen nematic and a frozen smectic polysiloxane with an orientational distribution of width ±18·5° and ±12·5°, respectively show no indication of the corresponding features, proving that the flip axis is fixed within ± 3° even after a large number of flips.

ISSN:0267-8292    

DOI:10.1080/02678299308027313

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Nuclear spin relaxation of quadrupolar nuclei provides access to a wide range of properties of lyotropic liquid crystals, ranging from the molecular ordering and dynamics at the interface to the macroscopic viscoelastic behaviour. We emphasize here the unique capability of the spin relaxation method to provide detailed geometric and dynamic information relating to the microstructure of lyotropic liquid crystals, i.e. the metric, curvature, and fluctuations of the dividing interface that separates polar and non-polar regions. This information is conveyed to the spin system via the translational diffusion of surfactants or counterions over the interface. The general principles of the spin relaxation method, as applied to lyotropic liquid crystals, are described, with emphasis on the model-independent information content of the relaxation observables and on the relation to microstructure. Specific results for lamellar, hexagonal, cubic, and nematic phases are also described.

ISSN:0267-8292    

DOI:10.1080/02678299308027314

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Langmuir monolayers at the air/water interface are distinguished by their richness of phases. These can be assigned to smectic categories, although the dominant competing interactions are not yet well elaborated. For single chain compounds, there are van der Waals attractions of the chains and repulsive forces of the head groups competing in determining the local structure. For larger molecules like phospholipids there appear also to be important dipolar interactions of the head groups. In order to study these interactions, we report surface X-ray diffraction studies of films of fatty acids and phospholipids at the air/water interface, with varying environmental parameters, as well as head group size and shape. We observe a wealth of mesophases and also the influence of molecular chirality on the structure. The defined control of the monolayer structure can be made use of to control crystal formation by diffusion from the subphase and nucleation at the interface. This is studied spectroscopically, microscopically andviaelectron diffraction of transferred films of cyanine dyes. In that case one observes epitaxy between the dye crystal and surfactant layer, and the relative lattices can be varied via suitable dye mixtures. A very peculiar interfacial influence results from the orientation of molecular dipoles at the interface. This causes long-range repulsive interactions leading to periodic superlattices in two phase coexistence regions. These forces are observed and quantified via fluorescence microscopy.

ISSN:0267-8292    

DOI:10.1080/02678299308027315

出版商:Taylor & Francis Group    

年代:1993

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:10.1080/02678299308027299

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor