Local-field anisotropy in cholesteric liquid crystals

The first experimental values of the Lorentz tensor components L _j for the cholesteric and smectic A phases of derivatives of cholesterol have been obtained using the dispersion of the refractive indices in the visible range. The temperature dependence of the components L _j has been determined; it is invariant with respect to the cholesteric-smectic A phase transition. The effect of the isotropization of the Lorentz and local field tensors with decreasing anisotropy of the molecular polarizability has been revealed.     

Local-field anisotropy of a light wave in quasi-two-dimensional soft-matter objects

Experimental values of the Lorentz tensor components L _j for uniaxial quasi-two dimensional “soft matter” objects on substrates (bilayer lipid membranes, multilayer Langmuir films, smectics A, hexatic smectics B, submicron films of discotics Col _hd , micron anisotropic films of liquid-crystal comblike polymers and macromolecular polymers, submicron films of conjugated conductive polymers), freely suspended submicron films of smectics A, and uniaxially stretched micron films of conjugated conductive polymers have been determined using dispersion of refractive indices in the visible range. The dependences of the components L _j on the type of orientation (axial, planar) of uniaxial molecules (structural units of the film) with respect to the optical axis of the film, the film thickness, the substrate type, the chemical structure of molecules, and their long-range orientational order are established. It is revealed that the smectic A-hexatic B phase transition and two-dimensional crystallization of the smectic layer lead to changes in the components L _j due to the change in the orientational ordering of molecules as a result of the relation between the orientational and hexatic order parameters. All the above objects are characterized by isotropization of the Lorentz tensor L and the local-field tensor f with a simultaneous decrease in the birefringence of the sample and in the anisotropy of the molecular polarizability due to the change in the electronic structure of molecules. The correction for the anisotropy of the local-field tensor f to the orientational order parameter or the anisotropy of the molecular polarizability increases. The existing model approaches to calculating the components L _j for the objects under consideration are compared with the experimental data.     

New manifestation of the statistical nature of orientation ordering in impure nematics

It is found that the splitting of polarized electron absorption bands of impurity dye molecules is inverted with temperature in a nematic liquid-crystal matrix. This effect is caused by the statistical nature of orientation ordering of impurity molecules and by the manifestation of higher order moments of the orientation distribution function.     

Development of contactless methods for directly measuring the temperature of nanoparticles of the active component in operating supported catalysts

In situ X-ray diffraction and spectroscopic methods for direct contactless measurement of the temperature of nanoparticles of the active component in operating supported catalysts are considered. These methods have provided convincing evidence that the temperature of nanoparticles of the active component may differ significantly from the support temperature during a very exothermic reaction.__________Translated from Kinetika i Kataliz, Vol. 46, No. 2, 2005, pp. 302–315.Original Russian Text Copyright © 2005 by Plyasova, Averyanov, Paukshtis, Kriger, Khasin, Parmon.     

Spectral features of impurity luminescence in uniaxial polymer films and nematic glasses

A study is conducted of the static shift and the splitting of the photoluminescence and electroluminescence polarized bands of uniaxial impurity molecules, embedded into uniaxial polymer films with axial or in-plane orientation of the impurity subsystem or into the vitreous phase of a nematic liquid crystal. Dependences of the band shift and the splitting on the type of alignment of impurity molecules, the polarization of transition moments in absorption and emission, and the host-impurity anisotropic interactions of different ranks are established. For both types of host matrices, characteristic features of orientational statistics of impurity molecules at a high degree of orientation ordering are studied. These features are revealed in a qualitative difference between the dependences of positions and splittings of polarized impurity fluorescence bands on the order parameter of the impurity molecules axially ordered in stretched polymer films and relevant dependences in nematic glasses. Specific features of the polarized impurity-related photoluminescence and electroluminescence in the matrices under study, observed experimentally, are interpreted.     

Orientational order and polarizability of molecules in a nematic liquid crystal

The influence of the orientational order of molecules in a nematic liquid crystal on the mean value $\bar \gamma$ and anisotropy Δγ of the molecular polarizability has been studied in the framework of the molecular statistical approach with allowance for the perturbation of the electronic structure of molecules due to the change in the conformation of their aromatic core and intermolecular interactions. Experimental dependences of $\bar \gamma$ and Δγ on the molecular orientational order parameter S have been derived, and their specific features for the known objects have been explained. The possibility of separating the contributions of opposite signs to the dependence Δγ(S) due to the change in the conformation of molecules and intermolecular interactions has been shown using nematic MBBA as an example.     

Basis of graded identities of the superalgebra M 1,2(F)

Denote by Mat _k,l (F) the algebraM _n (F) of matrices of order n = k + l with the grading (Mat _k,l ⁰ (F),Mat _k,l ¹ (F)), where Mat _k,l ⁰ (F) admits the basis $$ \{ e_{ij} ,i \leqslant k,j \leqslant k\} \cup \{ e_{ij} ,i > k,j > k\} $$ and Mat _k,l ¹ (F) admits the basis $$ \{ e_{ij} ,i \leqslant k,j > k\} \cup \{ e_{ij} ,i > k,j \geqslant k\} . $$ . Denote byM _k,l (F) the Grassmann envelope of the superalgebra Mat _k,l (F). In the paper, bases of the graded identities of the superalgebras Mat_1,2(F) and M _1,2(F) are described.     

Dependence of molecular polarizability on the orientational order in nematic liquid crystals

The dispersion dependences of refractive indices in the visible range were used to obtain experimental values of the Lorentz tensor components L _j and the mean molecular polarizability $ \bar \gamma $ \bar \gamma for five nematic liquid crystals belonging to two homological series. The dependence of L _j components on the homologue number, mesophase temperature, birefringence value, and the orientational order of molecules in the nematic phase and upon a nematic-smectic A phase transition was revealed. The effect of the isotropization of the Lorentz tensors and the local field tensor with decreasing birefringence and molecular polarizability anisotropy Δγ was confirmed. The quadratic dependence $ \bar \gamma $ \bar \gamma (S) on the molecular orientational order parameter S in the nematic phase was found. It was invariant with respect to the nematic-smectic A transition. The dependences $ \bar \gamma $ \bar \gamma (S) and Δγ(S) are explained within molecular statistical theory as consequences of the correlation between orientational and conformational degrees of freedom of molecules. These conformational degrees of freedom are related to the internal rotation of molecular fragments, which affects the electronic conjugation of the fragments and the oscillator strengths of molecular transitions.     

Local-field anisotropy in conjugated polymers

The experimental values of the Lorentz tensor components L _j have been obtained for uniaxial optically positive and negative films of conjugated polymers with thicknesses of tens of nanometers. The correlation between the components L _j and the measurable parameter η has been revealed and the analytical dependence L _j (η) has been derived in agreement with the experiment.     

Optical spectra of hydrogen plasma at electron concentrations above 1019 cm−3

The optical spectra of a dense (nonideal) plasma formed in a pulsed discharge in a closed quartz capillary were studied. The emission spectra of pure hydrogen plasma at a temperature of 23000 K and an electron concentration of ～1.5×10¹⁹ cm^?3, twice the value achieved earlier, were obtained. The plasma diagnostics was carried out by spectroscopic methods taking into account the radial inhomogeneity of the plasma column. The spectral intensity measured in the Balmer region (300–800 nm) was found to be lower than that calculated by the model of weakly nonideal plasma, an effect not observed at lower densities. Possible reasons for the discrepancy between the experiment and the calculation were considered. One of them being the specific density effect of a relative rise in plasma transmission with increasing density.