Vol 53, No 1 (2019)

Crystallization processes that occur during the drying of droplets of solutions by treating with nanosecond spark discharges have been experimentally investigated. It has been shown that crystallization in the droplets under plasma treatment proceeds in a different way than in identical droplets dried in the conventional mode.

Spectral and photochemical properties of bichromophoric dyad with two styrylquinoline (SQ) photochromes bridged by the decamethylene group have been investigated. According to stationary spectrophotometry data, there is no substantial interaction between the two SQ units of the dyad in the ground (S₀) state. Under irradiation, two competitive reversible reactions occur: trans-cis photoisomerization of the SQ photochrome and intramolecular [2+2] photocycloaddition between two SQ photochromes, indicating the transient formation of excimer. A comparison with results of model studies and earlier obtained data leads to the assumption that the excimer formation is facilitated by covalent bridging of the SQ photochromes by the decamethylene chain, whereas π-staking between the two SQ photochromes does not seem to play a substantial role.

The photochromic properties of new di- and tetranitrobisspiropyrans have been studied. Dinitrobisspiropyran solutions are characterized by direct photochromism, whereas reverse photochromism—coloration of the solution in the dark and its discoloration under the action of visible or UV light—is observed in solutions of tetranitrobisspiropyran in polar and weakly polar solvents and in polymer matrices of poly(methyl methacrylate) (PMMA) and polyvinyl butyral (PVB). The features of reverse photochromism are discussed, and a comparison with the photochromism of model nitrosubstituted monospiropyrans and dinitrobisspiropyran is carried out.

The influence of 1,6-hexanedithiol as an additional short-chain stabilizing ligand on fluorescence blinking of semiconductor colloidal quantum dots InP@ZnS has been studied using the analysis of the fluorescence decay curves. The optimum proportion of 1,6-hexanedithiol in the mixture has been determined. The influence of the thickness of the ZnS shells and the diameter of the InP core has been also studied. Correlation of these dependences with the analogous dependences for the luminescence quantum yield is observed.

The aim of this work was to develop chemosensors by analogy with bioreceptors based on lipid membranes stabilized on silica gel nanoparticles. Dansylglycine (DG) and a host–guest complex of DG with cucurbituril CB[8] were used as receptor fluorophores, and naphthalene and trimethylamine (TMA) in a gas phase were used as analytes. Stabilized lipid bilayers (SLBs) were obtained by the sorption of bilayer liposomes on nanoparticles under conditions that ensure the rupture of liposomes and the formation of a flat bilayer. The binding of CB[8] to SLB was performed for the first time and detected by measuring the fluorescence of the thiazole orange complex with CB[8] in a supernatant. The formation of the DG@CB[8] complex in water and a membrane manifested itself in F_DG quenching and a shift of the F_DG maximum toward short or long waves in water and in the membrane, respectively. On naphthalene excitation at 290 nm, the F_DG response was due to energy transfer from naphthalene to DG. The F_DG sharply decreased in the presence of TMA–H₂O vapors, but it increased above the initial value upon the removal of H₂O vapor. It was found that, unlike dyes embedded in a lipid matrix or sorbed on nanoparticles, the F_DG response for host–guest complexes was proportional to analyte concentration, and the F_DG wavelength did not change with analyte concentration.

A new approach to the creation of superhydrophobic surfaces is proposed. The principle of the method is based on the phase separation in a composite, one of the components of which “pushes” another component onto the surface during melting, wherein the latter component remains in the solid state and has a particle shape that ensures the appropriate surface roughness. A composite of polytetrafluoroethylene (meltable component) with few-layer graphene nanoplatelets has been taken as an example.

Optical properties and features of holographic recording upon photopolymerization of thin (about 1 μm) films based on acrylamide derivatives of polyfluorochalcones on a glass substrate have been investigated. The spectral sensitivity regions (350–400 nm) and refractive index (n = 1.647) of the films have been determined. It has been shown that these films allow the holographic recording of a diffraction grating with a diffraction efficiency of 59% and a width of the angular selectivity contour of 46° after washing out the nonpolymerized material in an organic solvent.

The mass spectrum of negative ions due to resonance electron capture by molecules of tetracyanoquinodimethane (TCNQ), a well-known electron acceptor, has been recorded in order to identify the dissociation processes of TCNQ molecular negative ions on the surface of an ionization chamber at thermal energies of electrons to be attached to the molecules. It has been found that the TCNQ molecular negative ions, preliminarily generated in the gas phase at several resonance maxima, reach the ionization chamber walls owing to a long extra-electron autodetachment lifetime ranging from 25 s in the first resonance at zero electron energy to 0.2 s in the resonance at 3.3 eV and dissociate at the walls as a result of the influence of the surface on the energy balance of the dissociation process. It has been taken into account that without the surface effect on the energy balance, this dissociation would be impossible because of an insufficient energy of the electron captured by the molecule. By B3LYP/6-311G calculations, the most probable dissociation pathways have been determined for negative fragment ions with various empirical formulas. The data obtained can be used to solve problems related to the properties of the TCNQ molecule in interaction with the conductive surface of a metal substrate in electronic devices.

The defect formation in AlN ceramics by bombarding with Fe⁺⁷ ions at a fluence ranging from 1 × 10¹¹ to 1 × 10¹⁴ ion/cm² has been studied. Changes in the main crystallographic characteristics, a decrease in the Griffiths criterion, and an increased in average stress as a result of irradiation are due to the appearance of additional defects in the structure and their subsequent evolution leading to changes in the degree of crystallinity. Pyramidal hillocks with an average height of 17–20 nm are observed to form on the surface of samples irradiated with Fe⁺⁷ ions at a fluence of 1 × 10¹¹ ion/cm².

The contact properties, chemical structure and surface morphology of poly(ethylene terephthalate) films modified by direct-current discharge at the cathode and anode have been studied. A substantial improvement in wettability and an increase in total surface energy and its polar term, which are retained upon storage in air at ambient conditions, have been shown. The change in the chemical structure of the plasma-modified films has been studied by X-ray photoelectron spectroscopy, and the formation of a significant amount of oxygen-containing groups on the surface has been demonstrated. The investigation of the modified films by atomic force microscopy and scanning electron microscopy has provided revealed a change in morphology of the surface and an increase in its roughness.