Orientation of lamellar phases of lyotropic multicomponent mixtures, based on cetyltrimethylammonium bromide cationic detergent, in magnetic field

The orientation of the lamellar phases in lyotropic systems based on cetyltrimethylammonium bromide (CTAB) detergent has been studied by polarization optical microscopy and ²H-NMR methods. The lamellar lyotropics studied are shown to align under a strong magnetic field of 11.7 T. According to ²H-NMR data, structural transformations of the lamellar phases may occur during orientation when the sample temperature increases.     

Identification of nematic lymoesophases with discotic and cylindrical micelles in lyotropic amphiphilic systems

Nematic lyomesophases with discotic (N _D) and cylindrical (N _C) micelles in complex multicomponent lyotropic systems based on alkyltrimethylammonium bromide detergents have been identified by the ¹H-²H-, and ¹³C-NMR methods and polarizationoptical microscopy. The difference in the structures of the N _D and N _C nematic phases is especially pronounced in the ¹³C-NMR spectra. Addition of chiral dopants to the lyomixture facilitates formation of the Ch _D and Ch _C cholesteric phases. According to the ¹³C-NMR spectra, the micellar mobility in the cholesteric lyomesophases decreases in comparison with the nematic ones. The alignment of lyocholesterics under the action of an external magnetic field is found.     

X-ray study of the structure of multicomponent glasses based on mining-industry waste

The short-range order and microinhomogeneity structure of laboratory samples of glasses belonging to the diopside-orthoclase-apatite system with different percentages of components were investigated by X-ray diffraction and small-angle scattering. A correlation between a change in the chemical composition of a glass, causing its segregation, and the short-range order parameters was ascertained: an increase in the apatite content leads to a change in the short-range order parameters. The use of the X-ray small-angle scattering technique made it possible to reveal inhomogeneities of electron density in the glasses under study and the dependence of the sizes of inhomogeneities on the glass composition.     

The significance of X-ray investigations for the classification of multicomponent systems with mixed crystals in a solid phase

The X-ray investigations of solid phases in the multicomponent systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O were conducted and the crystal lattice parameters of mixed crystals forming in these systems were determined. It was confirmed that in the KCl KBr H₂O system the continuous solid solutions were formed and in the K₂SO₄ (NH₄)₂SO₄ H₂O system the solid solutions with a miscibility gap were formed. In the KNO₃ NH₄NO₃ H₂O system the presence of two series of mixed crystals, namely the mixed crystals between ammonium nitrate and the double salt KNO₃ · 2 NH₄NO₃ and between potassium nitrate and the same double salt was confirmed. In this system a wide region of discontinuity (for x_NH4NO₃ = 0.083 – 0.67) also occurred. According to Roozeboom's classification, the KCl KBr H₂O system belongs to the 3^rd type, the K₂SO₄ (NH₄)₂SO₄ H₂O to the 5^th type (the discontinuous mixed crystals, the systems of peritonic type) and the KNO₃ NH₄NO₃ H₂O system is not comprised in this classification.     

Quasicrystalline and related phases in titanium based alloy systems

Amongst the non-aluminium based quasicrystalline alloys, investigations of titanium containing alloys in regard to the occurrence and stability of quasicrystalline phases have aroused considerable interest in recent years. Employing X-ray and TEM techniques a systematic investigation of the influence of substitution for Fe by Si and Ni on the stability of icosahedral phase in rapidly quenched Fe-Ti alloy has been carried out. The occurrence of metastable phases including commensurately modulated phase and the decagonal phase in Fe-Ti-Si system have been found. In addition, the occurrence ofstructural disorder manifested by arcs of diffuse scattering in diffraction patterns and anisotropy in the shape of idffraction spots has also been pointed out. It has been observed that 6 at.% of Si in Fe-Ti-Si system results in the formation of single-phase icosahedral quasicrystals. We have shown that contrary to some earlier reported results on Ti₂Ni, Ti₂Ni(Si) and Ti₅₆Ni₂₃Fe₅Si₁₆ alloys do not possess the icosahedral phase. In Ti₆₈Fe_26−xNi_xSi₆ alloy system, icosahedral phase formation ability is limited to the value of x < 9. The occurrence of icosahedral phase in these alloy systems has been analysed in terms of e/a ratio.     

Effect of magnetic field on lyotropic nematic in the vanadium pentoxide (V2O5)-water system

The optical textures of anisotropic phases of dispersed aqueous vanadium pentoxide solutions have been studied. It was established that the application of a magnetic field to these phases results in the formation of transient magnetohydrodynamic domains. The evaluation of the Freedericksz threshold field for the S-effect provided the determination of the elastic constant, K ₁ ≈ 3.6 × 10^?7 dyn. It is concluded that the studied anisotropic phases can be related to nematics.     

Electrical elements of the optical systems based on hydrogel - electrochromic polymer composites

Abstract

The results of studies of the electrically controlled elements of optical systems based on hydrogel - electrochromic polymer with conjugated π-electron system are shown. One important feature of conjugated polymers is the ability to change their optical characteristics under an external electric field. The electrochromic effect of these polymers may find applications in optical gating and filtering systems, optical sensors, ‘‘smart windows’’, optical memories, IR-switching, and electrochromic displays. Such electrochromic polymers were embedded in the matrix of a macroporous polymer hydrogel by the oxidative chemical polymerization method. The obtained samples based on hydrogel - polyaniline and hydrogel - polyorthotoluidine composites demonstrate the electrochromic behavior. In these composites, the electrolyte, as well as the electrochromic polymer, are located directly in the volume of hydrogel.     

Modification of the malus law for the torsional deformation of lyotropic nematics in magnetic field on the basis of statistical approach

A method based on the statistical approach is proposed to calculate the light intensity for the torsional deformation of lyotropic nematic liquid crystals at violated Mauguin adiabatic approximation. Theoretical dependences of the light intensity on the magnetic field strength are obtained for two limiting cases of lyotropic nematic anchoring with bearing surfaces: infinite and low anchoring energies.     

Formation of partially ordered organic planar systems based on the in situ control of their structural organization

The possibilities of significantly improving the quality of planar systems based on photoactive porphyrin–fullerene dyads, layers based on cytochrome c and cardiolipin, and lysozyme crystals and films using a complex of in situ X-ray methods and simulation are described. The potential of X-ray phase-sensitive and surface-sensitive methods developed by M.V. Koval’chuk and researchers from his school in monitoring all stages of synthesis of partially ordered organic structure is demonstrated. This approach shows its efficiency for in situ studies: starting from the formation of complexes in solutions up to the growth of protein films and crystals.     

Mathematical model of compensation for dispersion of light polarization states in electrooptical systems based on chiral liquid crystals

Spectral dispersion of the polarization states occurs after passage of linearly polarized light through a thin layer of a chiral nematic crystal along the helical axis. It is clearly pronounced for crystals with a high optical anisotropy and a helical pitch somewhat larger than the light wavelength. The results of numerical analysis of the spectral dependence of polarization states at the output of the liquid crystal layer and the method for compensating for the dispersion are presented for the first time. It is shown that polarization dispersion can be eliminated using phase plates of two types, one of which should have a high anomalous birefringence dispersion. The possibility of developing fast light modulators operating in a wide spectral range is discussed.     

Dielectric and thermal–mechanical properties of hybrid organic–inorganic polymer systems based on isocyanate-containing oligomers

Hybrid organic–inorganic polymer systems (OIS) were obtained in reactions of the organic oligomer (macrodiisocyanate + poly(isocyanate) (MDI + PIC)) which has free isocyanate groups with inorganic oligomer – sodium silicate (SS). The structure of OIS was formed as two interpenetrated networks: an elastic network as a result of reactions MDI–SS and a rigid network PIC–SS. Depending on MDI/PIC ratio, one of the network features is prevailing as attested to by dielectric, electrical and thermal–mechanical experiments. The elastic network MDI–SS possesses high values of dielectric parameters ε′, tan δ and conductivity σ whereas for the rigid network PIC–SS the values of these characteristics are much lower and are typical for usual thermosets.     

Effect of anharmonicity on the diffusion in glassforming binary Lennard-Jones systems

The correlations between some macroscopic and microscopic properties of model glass-forming materials are investigated using molecular dynamics simulations. Dynamics of three different binary mixtures of Lennard-Jones atoms, which differ only in the curvature of their particle–particle interaction potentials are reported. In the framework of the Coupling Model, we show that the capacity for interparticle coupling and anharmonicity of the potential are responsible for the behavior of the fragility and fast dynamics using both the diffusion coefficient and the non-ergodicity parameter.     

A comment on the Kawabata theory of magnetoresistance in disordered systems

The theory of magnetoresistance in three-dimensional disordered systems formulated by Kawabata is discussed. The final form of the formula for the magnetoconductivity which is commonly used for fitting to the experiment has been proven to be incorrect and its agreement with experiment rather accidental. A revision of the theory of magnetoresistance is suggested.     

Effect of finishing methods on surface roughness and color stability in all-ceramic systems

The objectives of the study were to evaluate the effect of the finishing methods on the surface roughness, and to investigate changes in CIE L*a*b* color coordinates of all-ceramic systems after different finishing methods and accelerated aging. Sixty specimens were prepared, 20 specimens each for Vitadur-N, IPS Empress II, and Cerec Vita Block Mark II. The surface roughness (Ra) following treatment with the different finishing methods was measured using a profilometer. Surface examinations in all groups were made by using a scanning electronic microscope. CIE L*a*b* values of the specimens were determined. After all specimens were subjected to accelerated aging, color measurements were repeated, and the total color differences (ΔE) were calculated. Data were analyzed statistically. Significant differences in surface roughness among all-ceramics were found (P < 0.05). No significant differences were found between the surface roughness of the glazed and polished all-ceramics (P > 0.05). After accelerated aging, all groups had acceptable color changes (ΔE < 2).     

Influence of active afterheater on the induction heating process in oxide Czochralski systems

Different shapes and orientations of an active afterheater for oxide Czochralski crystal growth systems are considered and corresponding results of electromagnetic field and volumetric heat generation have been computed using a finite element method (Flex‐PDE package). For the calculations, the eddy current in the induction coil (i.e. the self‐inductance effect) has been taken into account. The calculation results show the importance of an active afterheater, its shape as well as its geometry and position with respect to the crucible on the heat generation distribution in a CZ growth system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of heat treatment on spectroscopic properties of Er in multicomponent ZrF4-ZnF2-AlF3-YF3-MF2 (M = Ca, Sr, Ba) based glass

Er³⁺ doped multicomponent fluoride based glass was prepared. These precursor fluoride glass samples were then heated using different schedules. Crystalline phase particles were successfully precipitated in the multicomponent fluoride glass samples after heat treatment. The influence of heat treatment on the spectroscopic properties of Er³⁺ in multicomponent fluoride based glass samples were discussed. Small changes of the Judd-Ofelt parameters Ω_i (i = 2, 4, 6) were found in multicomponent fluoride glass samples before and after heat treatment compared to oxyfluoride telluride glass. Preparation conditions used to produce transparent multicomponent fluoride glass ceramics doped with rare-earth ions are discussed.     

Bulk metallic glasses based on rare-earth elements in lanthanum series

A series of bulk metallic glasses (BMGs) based on the rare-earth (RE) elements in lanthanum family have been obtained by a copper mold casting method. These chemical comparable RE elements with ‘continuous’ range of atomic size, electron structure and elastic constants may provide a good system for systematically exploring the BMG-forming characteristics. The glass-forming ability, elastic properties, thermal stability and their correlations in the RE-based BMGs have been investigated.