Electrochemical Properties of Overoxidized Poly-3,4-Ethylenedioxythiophene

The properties of poly(3,4-ethylenedioxythiophene) (PEDOT) films were studied electrochemically at high positive potentials (from–0.3 to 1.5 V relative to the Ag/AgCl electrode). A cyclic voltammetry (CV) study revealed the range of potentials (up to 1.3–1.5 V) where the cycling leads to significant changes in the electrochemical, structural, and morphological properties of the polymer film due to overoxidation. When the upper cycling potential E_up exceeded 1.4 V, the anodic current significantly increased during the first cycle and then decreased, which suggests a loss of the electroactivity of the polymer and degradation of its properties. In the high-frequency region of the impedance spectra of the PEDOT films, a semicircle appears after overoxidation, which indicates a notable increase of the charge transfer resistance in the system, in contrast to the films subjected to potentiodymanic processing in a limited range of potentials from–0.3 to 1.3 V. The effect of overoxidation on the polymer morphology was studied by scanning electron microscopy. The chemical state of elements in the structure of the polymer film was determined by X-ray photoelectron spectroscopy. The obtained data indicate that–S=O groups formed at the thiophene sulfur in the polymer.

     

Spectrum of natural electromagnetic waves in a periodic ferromagnet-dielectric structure

The specific features of propagation of natural TE waves in a periodic ferromagnet-dielectric structure are investigated in the following geometry: a bias magnetic field is parallel to the ferromagnet/dielectric interface and perpendicular to the wave propagation direction. The transformation matrix for the period of the structure, the dispersion relation, and the energy reflection coefficient are obtained for the case of normal incidence of a wave on a semi-infinite periodic medium by solving the boundary-value problem. It is shown that an external field can be used to control the spectrum and characteristics of reflected waves.     

Crystal structure of <Emphasis Type="Italic">p</Emphasis>-carboxyphenylhydrazone benzoylacetone

The crystal structure of p-carboxyphenylhydrazone benzoylacetone is determined. The crystals are monoclinic, a = 13.614(4) Å, b = 11.388(2) Å, c = 20.029(6) Å, β = 104.82(2)°, V = 2339(9) ų, Z = 8, space group C2/c, and R = 0.038 for 1622 reflections with I > 2σ(I). The crystal is built of C₁₇H₁₄N₂O₄ neutral molecules that are linked by O-H?O hydrogen bonds between the carboxyl groups into centrosymmetric pseudodimers. The effect of carboxylation of the phenylhydrazone fragment and the position of the carboxyl group on the molecular packing in the crystal is determined. The N(1)-H(1N)?O(1) intramolecular hydrogen bond (N-H, 0.94 Å; H?O, 1.87 Å; N?O, 2.59 Å; and the N-H?O angle, 133°) is formed in the molecule.     

Dispersion of single-walled carbon nanotubes in dimethylacetamide and a dimethylacetamide–cholic acid mixture

A way of dispersing single-walled carbon nanotubes in preparing stable suspensions with high concentrations of individual nanotubes in amide solvents is described. The obtained suspensions are studied via Raman spectroscopy. The dependence of the degree of single-walled carbon nanotube (SWNT) dispersion in individual and mixed amide solvents on the type of solvent, the mass of nanotubes, and the concentration of cholic acid is established. A technique for processing spectral data to estimate the diameters and chiralities of individual nanotubes in suspension is described in detail.     

Propagation of low-frequency waves in biological tissues and vessels

Elastic surface waves in biotissue are considered taking into account its structure, and dispersion dependences are presented. Effects of contact of vibroacoustic action on the soft tissue of a human’s arm are studied, and the biotissue activity manifests itself as a vibroreaction with different characteristic times. A thermodynamic approach to the construction of rheological relations of active mechanochemical media is described. Dispersion characteristics of acoustic processes in passive and active blood vessels are given.     

Designing Simple Tridentate Ligands for Highly Luminescent Europium Complexes

A series of tridentate benzimidazole‐substituted pyridine‐2‐carboxylic acids have been prepared with a halogen, methyl or alkoxy group in the 6‐position of the benzimidazole ring, which additionally contains a solubilising N‐alkyl chain. The ligands form neutral homoleptic nine‐coordinate lanthanum, europium and terbium complexes as established from X‐ray crystallographic analysis of eight structures. The coordination polyhedron around the lanthanide ion is close to a tricapped trigonal prism with ligands arranged in an up–up–down fashion. The coordinated ligands serve as light‐harvesting chromophores in the complexes with absorption maxima in the range 321–341 nm (ε=(4.9–6.0)×10⁴ M ^?1 cm^?1) and triplet‐state energies between 21 300 and 18 800 cm^?1; the largest redshifts occur for bromine and electron‐donor alkoxy substituents. The ligands efficiently sensitise europium luminescence with overall quantum yields ( ) and observed lifetimes (τ_obs) reaching 71 % and 3.00 ms, respectively, in the solid state and 52 % and 2.81 ms, respectively, in CH₂Cl₂ at room temperature. The radiative lifetimes of the Eu(⁵D₀) level amount to τ_rad=3.6–4.6 ms and the sensitisation efficiency η_sens= (τ_rad/τ_obs) is close to unity for most of the complexes in the solid state and equal to approximately 80 % in solution. The photophysical parameters of the complexes correlate with the triplet energy of the ligands, which in turn is determined by the nature of the benzimidazole substituent. Facile modification of the ligands makes them promising for the development of brightly emissive europium‐containing materials.     

The volume characteristics and molecular dynamics simulation of nonaqueous solutions of aliphatic alcohols

The kinematic and thermodynamic characteristics of the methanol-heptane system were calculated by the molecular dynamics method at 300 K and heptane concentrations up to 0.095 mole fractions. An increase in the concentration of heptane was shown to stabilize the structure of methanol. The densities of aliphatic alcohol-alkane-electrolyte (nonelectrolyte) systems were measured experimentally at 298.15 K. The results were used to calculate apparent and partial molar volumes with errors of 0.01 cm³/mol. The dependences of volume properties on composition contained extrema in agreement with theoretical calculations.     

Mass tranfer of ions and solvent at redox processes in poly-3,4-ethylenedioxythiophene films

The work presents the data on mass transfer at the interface of the poly-3,4-ethylenedioxythiophene film with different propylene carbonate electrolyte solutions (TBAPF₆, LiClO₄, NaClO₄, TBAClO₄, TBABF₄) obtained using the quartz microgravimetry method in combination with cyclic voltammetry. It is shown that two parts of different nature can be observed in the region of electric activity of poly-3,4-ethylenedioxythiophene films on Δm, ΔQ curves. They evidence the change in mass transfer conditions at achieving different film oxidation degrees.     

Magneto-optical activity of a one-dimensional photonic crystal with a magnetic defect

The influence of a magnetic defect on the field distribution and magneto-optical properties of a one-dimensional photonic crystal has been investigated. It has been shown that the maximum localization of the wave field in the defect layer is achieved in an asymmetric photonic crystal structure. A greater Faraday rotation, which significantly exceeds the angle of rotation of the polarization plane in an isolated magnetized layer, and a higher degree of localization of the wave field can be achieved when the magnetic layer is surrounded by layers of photonic crystal mirrors with a lower refractive index. An increase in the Faraday rotation angle is determined not only by an increase in the thickness of the magnetic defect but also by a symmetric increase in the number of periods in the photonic crystal mirrors.