Yu. L. Moskvin

Direct fluorination of polystyrene films

Abstract Kinetics of fluorinated layer formation in polystyrene (PS) were investigated for various fluorine and oxygen partial pressures and temperatures. The PS direct fluorination process was shown to be diffusion-limited, i.e., the rate of the process is limited by fluorine penetration through the fluorinated layer. Dependence of fluorine permeability value and concentration of carbonyl groups in treated polymer on F 2 O 2 mixture composition were investigated. The inhibiting action of oxygen is due to C O groups formation. A scheme of elementary stages of the direct fluorination is proposed.

DIRECT FLUORINATION OF POLY(VINYL TRIMETHYLSILANE) AND POLY(PHENYLENE OXIDE)

Abstract Fundamental features of the direct fluorination of poly(vinyl trimethylsilane) (PVTMS) and poly(phenylene oxide) (PPO) have been investigated. The influence of the fluorination conditions (fluorinating mixture composition, treatment duration) and polymer molecular weight on the rate of formation of the fluorinated layer and on physical–chemical properties (chemical composition, density, refractive index, absorption spectra in the visible and UV, surface energy) was investigated.

Formation of free radicals in the low-temperature fluorination of polymers

The formation of free radicals in the process of direct fluorination of natural and synthetic polymers at temperatures close to 77 K was studied by ESR. The maximum concentrations of radicals, (1017–5·1018 spin g−1) and their complete oxidation were observed in the temperature interval from 77 to 250 K at a fluorine pressure of 30 Torr. The initiation of chain halogenation, which consists of homolytic breaking of chemical bonds to yield free-radical intermediates. was examined in the framework of the multi-center synchronous transitions model.

Kinetic analysis of photoelectrochemical hydrogen evolution over p-type silicon in acidic aqueous solutions of electrolytes

The kinetics of photoelectrochemical hydrogen evolution at p-Si single crystals in acidic aqueous solutions of electrolytes under pulse photoexcitation was studied. Despite a low stability of the silicon surface under the experimental conditions, a distinct interrelation between the characteristic time of interfacial charge transfer and stationary current was found. The determination of the characteristic transfer time does not need the detailed elaboration of generation-recombination processes in the semiconductor. The steady-state current density was shown to be determined both for the dark current and photocurrent by the surface charge density.

Transport Properties of Separating Membranes MF-4SK during Alkaline Electrolysis of Water

The transport properties of separating membranes MF-4SK are studied during electrolysis of H2O in solutions of KOH. The effective diffusion coefficients of molecules of KOH and H2O and the transfer coefficients of ions K+ and OH− and molecules of H2O are measured at KOH concentrations reaching 11 M, currents reaching 0.31 A cm−2, at ambient temperature and at 80°C. In contact with a KOH solution in the concentration interval 0.1 to 11 M, the membranes that initially swelled in H2O lose a considerable fraction of water that was present in them and the overall volume of clusters and solution-filled channels in them noticeably decreases. The coefficients of transfer by current of ions K+ out of anodic compartment into cathodic and the OH− ions in the reverse direction, respectively, happen to be equal to about 0.6 and 0.4 at ambient temperature and 0.8 and 0.2 at 80°C. The coefficients of transfer of water molecules out of the anodic volume into the cathodic volume in the process of electrolysis happen to be in the limits 1.6–1.9 at ambient temperature and in the limits 2.2–2.8 at 80°C. The effective diffusion coefficients of molecules of KOH and H2O at moderate concentrations of KOH (5.6 M) amount to ∼2.6 × 10−7 and 30 × 10−7 cm2s−1 at ambient temperature and ∼4 × 10−7 and 61 × 10−7 cm2s−1 at 80°C, respectively. At a high concentration of KOH (∼10 M) these quantities substantially diminish.

Dynamic characteristics of organic bulk-heterojunction solar cells

Transient characteristics of organic bulk-heterojunction solar cells have been studied using pulsed laser probing. An analysis of the photoresponse waveforms of a typical solar cell measured by varying load resistance within broad range at different values of the bias voltage provided detailed information on the photocell parameters that characterize electron-transport properties of active layers. It is established that the charge carrier mobility is sufficient to ensure high values of the fill factor (∼0.6) in the obtained photocells. On approaching the no-load voltage, the differential capacitance of the photocell exhibits a sixfold increase as compared to the geometric capacitance. A possible mechanism of recombination losses in the active medium is proposed.