Alexander V. Eletskii

Non-equilibrium and equilibrium problems in laser-induced plasmas

Abstract Several problems which can determine non-equilibrium effects in laser-induced breakdown plasmas are analysed in this study. In particular, we focus our attention on problems associated with the fluid dynamics of the expanding plume, with time-dependent collisional-radiative models for describing the population densities of excited states, with the time-dependent Boltzmann equation for characterizing the electron energy distribution function in laser-induced breakdown spectroscopy (LIBS) plasmas. The results show that these problems should be carefully taken into account for developing a calibration-free LIBS methodology. Finally, problems associated with equilibrium plasmas, and in particular the dependence of the partition function on the particular environment surrounding the different components of a plasma are discussed.

Emission properties of carbon nanotubes and cathodes on their basis

This paper reviews the main physical problems and the most important results related to the emission properties of carbon nanotubes (CNT) and cathodes on their basis. The phenomenon of electrical field amplification in the vicinity of a nanotube tip of various structures is studied quantitatively. The physical mechanisms responsible for deviation of the current–voltage characteristics of a nanotubes array from those for an individual CNT described by the classic Fowler–Nordheim relation have been considered. The types of arrangement of CNTs over the cathode surface are compared and analyzed in terms of the screening effect. The thermal effects limiting the emission current of a CNT-based cathode have been treated. The angular divergence of an electron beam emitted by a CNT caused by electron Coulomb repulsion has been evaluated.

Injected nanoparticles: The combination of experimental systems to assess cardiovascular adverse effects

When nanocarriers are used for drug delivery they can often achieve superior therapeutic outcomes over standard drug formulations. However, concerns about their adverse effects are growing due to the association between exposure to certain nanosized particles and cardiovascular events. Here we examine the impact of intravenously injected drug-free nanocarriers on the cardiovasculature at both the systemic and organ levels. We combine in vivo and in vitro methods to enable monitoring of hemodynamic parameters in conscious rats, assessments of the function of the vessels after sub-chronic systemic exposure to nanocarriers and evaluation of the direct effect of nanocarriers on vascular tone. We demonstrate that nanocarriers can decrease blood pressure and increase heart rate in vivo via various mechanisms. Depending on the type, nanocarriers induce the dilation of the resistance arteries and/or change the responses induced by vasoconstrictor or vasodilator drugs. No direct correlation between physicochemical properties and cardiovascular effects of nanoparticles was observed. The proposed combination of methods empowers the studies of cardiovascular adverse effects of the nanocarriers.

Growth of fractal structures in fullerene solutions

The phenomenon of formation of fractal cluster structures in fullerene solutions discovered in recent experiments is analyzed theoretically. As the basis for analysis the standard fractal cluster growth approach is used. The simplest approximation based on the supposed temporal independence of both fractal cluster dimensionality and attachment probability of two clusters does not provide agreement between the measured and calculated cluster growth data. A satisfactory agreement is attainable in a frame of the Reaction Limited Cluster Aggregation model in the supposition that the attachment probability γ depends on cluster size. The best fitting is obtained for the dependence γ = γ0(r0/R)α, where γ0 = 10−7, α = 2. The possible physical mechanism clarifying such a dependence is considered.

Diffusion of aggregated fullerenes in solution

The diffusion of fullerenes in solution is studied taking into account the recently established formation of clusters containing numbers of aggregated fullerence molecules. Based on a droplet model of a cluster, the distribution function of fullerence clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters diminishes as the concentration decreases. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerence C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.

Similarity laws and thermodynamic quantities for fullerite C60

Abstract The crystal structure of solid fullerite C 60 at temperatures exceeding 260 K is the face centered cubic one. The intermolecular interaction in this crystal is short range so each C 60 molecule interacts only with the nearest neighbors. Substances having the mentioned features form a class of those with some common properties. Thus the thermodynamic behavior of substances belonging to this class is governed by similarity laws in accordance with which the thermodynamic parameters are dimensionless functions of quantities constructed of the mokecular mass μ, temperature T , well depth in the intermolecular interaction potential D and equilibrium intermolecular distance R o . One of these similarity laws has been used to process known data related to the pressure vapor temperature dependences for fullerite C 60 . This permits a refinement of the magnitude D = 0.257 + 0.01 eV known up to now with more uncertainty. This magnitude is used for checking the fulfilment of similarity laws for those fullerite thermodynamic parameters for which experimental data are available. The fulfilment of similarity laws permits an estimation of the critical parameters, melting and boiling temperatures, bulk modulus and also the Debye temperature for fullerite. The obtained data are analyzed in terms of the possibility of the existence of fullerene in the liquid state.

Thermal diffusion of fullerenes in solutions

The phenomenon of the thermal diffusion of fullerenes in solutions concerned with the fact aggregation of fullerence molecules in clusters in organic solvents discovered recently is studied. The mechanism of this phenomenon based on the temperature dependence of the cluster size distribution function is proposed. The temperature and concentration dependencies of the cluster size distribution function calculated previously are used to calculate the thermal diffusion coefficient of C60 fullerene in toluene solution as a function of temperature and concentration. It is shown that the mechanism spoken of dominates in thermal diffusion at the temperature above the phase transition temperature in solid C60. A contribution of the conventional mechanism of thermal diffusion caused by a considerable difference in fullerene and solvent molecule dimensions is estimated.

The kinetics of the reaction of C60 and C70 fullerenes with sodium metal in toluene solution

Abstract The kinetics of the reaction of C60 and C70 with metallic sodium in toluene solution at room temperature has been studied. The initial stage of reaction gives the fullerene monoanion, and the ratio of the reaction rate constants k(C70)/k(C60) = 2.5 ± 0.1. This ration does not depend on the relative fullerene concentrations and absolute reaction rates, the latter being sensitive to the condition of the metal surface and so varies in an irregular manner. The possibility of using the difference in the reaction rate constants for the development of a fullerene separation and purification technology is discussed.

Isolation and characterisation of C70O

C70O has been isolated in ca. 0.5% yield by HPLC separation of the soot extract obtained from a novel arc-discharge reactor for fullerene production. The reactor (DC conditions) can be operated continuously for 24 h, employs a rotating cathode and an anode consisting of continuously-fed strips cut from a carbon sheet. The 13C NMR spectrum of C70O shows that two isomers (1,2-epoxy[70]fullerene and 5,6-epoxy[70]fullerene) are present in a ratio of ca. 43∶57 and all 37 peaks corresponding to each isomer have been identified. These are the first [70]fullerene derivatives in which 5,6-addition is preferred over 1,2-addition, this preference probably deriving from the considerable strain that accompanies bridging with a single atom; the greater curvature across the 1,2-positions compared with the 5,6-positions therefore disfavours the former. Differential polarisabilities of the electrons of the 1,2- and 5,6-bonds, a factor producing a variation in reactivity order according to the attacking reagent (but not considered hitherto in the context of fullerene chemistry) may also be significant. The epoxides are unstable towards EI mass spectrometry, in contrast to epoxides possessing additional addends, and this may reflect the reduced cage strain present in the latter.

Operational characteristics of a graphene-based electron field emitter

The electron work function for graphene fragments with pure edges and those functionalized by hydrogen atoms is calculated using the density functional theory method, and the obtained results are used to evaluate the current–voltage (I-V) characteristics of a vertically aligned rectangular graphene sheet. The calculated results of the electric potential spatial distribution in the vicinity of the graphene layer indicates a highly inhomogeneous distribution of the electric field amplification factor along its external edge, so that the maximum amplification occurs near the vertices of the layer. Such an inhomogeneity promotes a highly inhomogeneous distribution of the emission current along the graphene layer edge. At relatively low voltages, the emission is provided mainly by the region near the vertices of the layer, where the relative contribution of this region decreases with an increase in applied voltage. This effect manifests itself in a deviation of the emission I-V characteristics from the classic...