Spontaneous formation of stabilized 1,2-dicarboxyethyl free radicals in the solid system succinic acid-peroxydisuccinic acid

Conclusions A new phenomenon, viz. the spontaneous formation of stabilized 1,2-dicarboxyethyl radicals in a crystalline matrix during the complete removal of the solvent from a solution of PDSA and SA in water, methanol, or acetone, was discovered.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2018–2021, September, 1980.     

Conformation of perfluoroalkyl radicals in the solid phase

An equilibrium conformation of the perfluoroalkyl ∼CF₂·CF₂ radical at 77 K in matrices of polytetrafluoroethylene andn-perfluoroalkanes was studied. Upon cooling from 300 to 77 K at temperatures below 200 K, the ESR spectrum of this radical changes, and the well-resolved hyperfine structure appears. The hyperfine splitting constants on nuclei of two nonequivalent F_β atoms were determined: 2.2 and 1.1 mT, respectively. TheA _∥ andA _⊥ values for the F_α atoms are 22.5 and 3.3 mT, respectively. The conformational angle between the axis of the orbital of an unpaired electron and projection of the C_β−C_γ bond is 5.6°. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 331–334, February, 1999.     

The radiation yields of radicals in solid organic substances containing heteroatoms

EPR has been used to measure the radiation yields of radicals (G_R) in various classes of organic compounds containing heteroatoms: dialkyl disulfides, diphenyl- and dibenzyl disulfide, alkyl derivatives of thiophene, thiophenecarboxylic acids, halogen derivatives of thiophene, and saturated heterocyclic compounds containing nitrogen, oxygen, and sulfur atoms. It has been shown that 1) G_R=0.2–1 per 100 eV in saturated disulfides and cyclic sulfides, while G_R=3–8 per 100 eV in the corresponding hydrocarbons, alcohols, oxides, and alkyleneimines; 2) the introduction of a sulfur atom into aromatic compounds does not alter the radiation stability; 3) disturbance of the conjugation of halogen atoms and of the carboxyl group with the thiophene ring leads to a decrease in the radiation stability. It is suggested that the increased stability of sulfur-containing compounds may be due to the excitation of the electrons in the S atom at the d-orbitals, which lie appreciably lower in the sulfur atom than in the atoms of oxygen, nitrogen, and carbon, and the subsequent dissipation of the excitation energy.     

Identification of free radicals trapped in solid methacrylated resins

Photopolymerization of methacrylated dental resins at room temperature leads to the appearance of long‐life free radicals because of system vitrification. These free radicals were observed by electronic paramagnetic resonance (EPR), and their characterization was undertaken by reference to the reactional mechanism, from the comparison with the model EPR signal and from theoretical simulation. Overlapping of two EPR signals assigned to two different kinds of radicals because of methacrylate end groups accounted for all the experimental and theoretical results. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1691–1699, 2003     

Effect of aqueous phase structuring on the properties of model emulsion films stabilized with solid microsized particles

The thickness and stability of emulsion films stabilized with microsized silica particles are studied. The stabilization mechanism is shown to be realized via the formation of a thixotropic gel in a dispersion medium.     

Simulation of photochemical reactions of butadiene and calculation of the quantum yields

The photochemical reactions of butadiene-1,3 have been simulated. The calculated quantum yields of the products quantitatively agree with experimental data (deviation from the experimental data in on average less than 30%). The efficacy of the method in predicting photochemical processes of various types (isomerization, decomposition) occurring simultaneously via different pathways has been shown. It has been confirmed that the quantum beat frequency of resonating states can be used as a parameter of the method and, as such, allows obtainable quantitative estimates to be refined.     

Photodecomposition quantum yields of 3-chloro-3-methyldiazirine in the gas phase

A careful integration technique has allowed the determination of photodecomposition quantum yields Φ_D of 3-chloro-3-methyldiazirine at several wavelengths using conventional equipment. The results obtained are

A change of collision frequency from 5.0 × 10⁷ to 5.7 × 10¹⁰ does not alter the quantum yield which is also unaltered by oxygen. Our data are explained by a mechanism which includes two photodecomposition paths. The first is a direct photodissociation from the electronic state reached by the initial transition and the second involves methylchlorocarbene.     

Non-linear effects in the quenching of fluorescent quantum dots by nitroxyl free radicals

Quenching of quantum dot luminescence by nitroxides is extremely non-linear and dependent on nanoparticle size, being most effective for the smaller particles; it is proposed to involve an electron exchange mechanism.     

Regarding the effect that different twin-tailed surfactant have on a solid stabilized petroleum emulsion

An industrial petroleum emulsion stabilized by colloidal silica particles was treated with four different twin-tailed surfactants: sodium bis-2-(ethylhexyl) sulfosuccinate (AOT), didodecylammonium bromide (DDAB), calcium oleate (Ca(OL)₂), and dioctadecyldimethylammonium bromide (DODAB). Fourier transform infrared (FT-IR) spectroscopy, optical microscopy, centrifuge test, and conductivity measurement were employed to determine the effect of the amphiphile molecules on the crude oil emulsion. AOT and DDAB produce emulsion breakdown, while Ca(OL)₂ does not alter the emulsion stability and DODAB produces an extra stabilization of it. The AOT adsorption at the oil–water droplet interface is a spontaneous process (ΔH^ads < 0), which promoted the emulsion breakdown through an inter-droplet interaction mechanism. DDAB needs extra energy (via centrifugation) to destabilize the emulsion. Ca(OL)₂ dissolves in oil phase and remains there without altering the emulsion strength, while DODAB increases the emulsion stability.     

Fluorescence decay times and quantum yields for benzene in the solid and vapour phases

Fluorescence decay-tune measurements of solid benzene at very low temperature give a value of 83.8 ns which is similar, within experimental error, to the high-pressure value of benzene vapour reported in the literature. The agreement in the fluorescence quantum yield is discussed     

The effect of crosslinking on the reactivity of free radicals in isotactic polypropylene

Isotactic polypropylene of various degrees of crosslinking was prepared using high concentrations of dicumyl peroxide as the crosslinking agent. Free radicals were generated by γ irradiation of crosslinked iso-PP with a dose of 2.4 Mrad. It was found that the rate constant for free-radical decay is independent of crosslinking in the temperature range from ?30 to +20°C. The result is discussed from the point of view of degradation processes taking place simultaneously with crosslinking of iso-PP.