Interaction of single-walled carbon nanotubes with sulfuric acid

An increase in the radiation yield of paramagnetic centers in H₂SO₄ + nanotubes (NTs) solutions was evidence of the sensitizing influence of NTs on the low-temperature radiolysis of sulfuric acid, that is, on excitation energy and charge transfer. Under the conditions selected, the influence of NTs extended to distances of 100–300 nm. The presence of NTs also influenced the interstice nanodiffusion of atomic hydrogen by decreasing kinetic heterogeneity of the vitrified matrix surrounding NTs. No chemical interaction between atomic hydrogen and carbon NTs was observed at 77–120 K. The diffusion of radical-base anions occurred following the vacancy mechanism and was independent of the presence of NTs. Nanotubes did not form a separate phase as sulfuric acid solutions were cooled to 77 K. The transition from the vitreous to supercooled liquid state was observed as irradiated and nonirradiated solutions were heated to 175 K; no phase transitions occurred over the temperature range 180–300 K. For the first time, substantial changes in the electronic spectra of sulfuric acid solutions of NTs with time were observed: an intense additional absorption band at 320 nm appeared in the spectra in several days. This band was supposedly related to the formation of complexes between H₂SO₄ molecules and the surface of NTs.     

Mechanism of the initiation of low-temperature radiation telomerization of tetrafluoroethylene in hexafluoroisopropanol

ESR and IR spectroscopy and scanning calorimetry are used to investigate the mechanism of low-temperature radiation telomerization of tetrafluoroethylene (TFE) in hexafluoroisopropanol (HFIP). It is found that the low-temperature telomerization of TFE in HFIP proceeds via an ion-radical mechanism. This process is initiated by the radical anions (CF₃)₂C^·-O^? formed during the deprotonation of OH groups of primary hydroxyl radicals (CF₃)₂C^·-OH exhibiting strong acidic properties. An interpretation of ESR spectra of irradiated HFIP recorded at 230–240 K is proposed with regard to the anisotropy on β-fluorine atoms and estimates of the angles between the corresponding C-F bonds and the axis of the unpaired electron orbital.     

Radiation-chemical synthesis of tetrafluoroethylene telomers in chloropentafluorobenzene and perfluoroxylene

The kinetics of radiation-induced telomerization of tetrafluoroethylene in chloropentafluorobenzene and perfluoroxylene have been studied. Colloidal solutions of thermally stable tetrafluoroethylene telomers with a chain length of 50–160 units have been obtained. A comparative analysis of the reactivity of some monohalogenated benzene derivatives used as telogens has been performed.     

Spontaneous polymerization of acrylamide in glycerol

The spontaneous polymerization of acrylamide in glycerol in the range of 250–350°C has been first observed and investigated. It has been shown that the polymerization proceeds during dissolution of acrylamide in glycerol and leads to formation of gel globules in which the growth of polymer chains takes place. The reaction occurs without termination of kinetic chains in the living polymerization mode. The effective chain transfer at a low concentration of active centers ensures a high yield of the polymer.     

Effect of tungsten film on electro-physical properties of silicon after annealing at 1100°C

We investigated changes in the bulk electro-physical properties of crucibleless silicon after repeated annealing at 1100°C both with and without a tungsten film on the surface. We observed much less change in the resistivity of samples with tungsten films than in those with no films. We observed a significant (about a factor of 10) reduction in the photoresponse decay time, and an increase in the spectral band in which there is a photocurrent as compared with the uncoated samples. The photoconductivity as a function of temperature exhibits a power-law dependence, with β₁=(1.75±0.06) and β₂=(0.20±0.03) for coated and uncoated samples. The change in the relaxation time of the stationary photoconductivity of coated samples is a nonmonotonic function of the intensity of the uniform illumination. Engineering Physics Institute, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 42–46, May, 1996.     

Radiation-initiated telomerization of tetrafluoroethylene in acetone at a constant monomer concentration

Kinetics of radiation-initiated polymerization of tetrafluoroethylene in acetone was studied at various initial concentrations (pressures) of the monomer in the reactor, which remain constant in the course of synthesis. Concentrated solutions of tetrafluoroethylene telomers were obtained and their properties were examined.     

Giant effect of uniaxial pressure on magnetic domain populations in multiferroic bismuth ferrite

Neutron diffraction is used to show that small (～7 MPa, or 70 bar) uniaxial pressure produces significant changes in the populations of magnetic domains in a single crystal of 2% Nd-doped bismuth ferrite. The magnetic easy plane of the domains converted by the pressure is rotated 60° relative to its original position. These results demonstrate extreme sensitivity of the magnetic properties of multiferroic bismuth ferrite to tiny (less than 10(-4)) elastic strain, as well as weakness of the forces pinning the domain walls between the cycloidal magnetic domains in this material.     

Local weak ferromagnetism in single-crystalline ferroelectric BiFeO3

Polarized small-angle neutron scattering studies of single-crystalline multiferroic BiFeO(3) reveal a long-wavelength spin density wave generated by ～1° spin canting of the spins out of the rotation plane of the antiferromagnetic cycloidal order. This signifies weak ferromagnetism within mesoscopic regions of dimension 0.03 microns along [110], to several microns along [111], confirming a long-standing theoretical prediction. The average local magnetization is 0.06 μ(B)/Fe. Our results provide an indication of the intrinsic macroscopic magnetization to be expected in ferroelectric BiFeO(3) thin films under strain, where the magnetic cycloid is suppressed.     

Thermokinetic Oscillations of the Rate of Radiation-Induced Cryochemical Solid-Phase Chain Reactions

Data on the detection and the experimental and theoretical investigation of thermokinetic rate oscillations in cryochemical chain reactions induced by radiation (⁶⁰Co -rays) in a solid phase are surveyed. Such oscillatory modes follow the general pattern and they are observed for different reactions (hydrobromination, polymerization, and copolymerization of ethylene) in crystalline and glassy states both immediately in a -radiation field and as a post effect upon heating of samples.