A.A. Onischuk

Evolution of structure and charge of soot aggregates during and after formation in a propane/air diffusion flame

Abstract Evolution of soot aggregate morphology, size and concentration is investigated during and after formation of soot in propane/air diffusion flame. Monitoring of gaseous intermediates in the flame is done by gas chromatography. Soot aggregate size and morphology are analyzed by a transmission electron microscope; soot number concentration is determined by an automated diffusion battery. Aggregate–aggregate collisions and aggregate structural transformations are observed in real time using a video system. It is determined that soot aggregates formed in flame are charged. The electric charge per aggregate is determined by video observation of aggregate movement in electric field. Both positively and negatively charged aggregates are formed. Typical net charge per aggregate is a few elementary units. An effect of soot aggregate restructuring from chain-like to compact structures is observed. It is determined that the driving force for this restructuring is Coulomb interactions between different parts of the aggregate. It is demonstrated that Coulomb interactions between aggregates can affect considerably coagulation process and the final aggregate shape.

AEROSOL FORMATION UNDER HETEROGENEOUS/HOMOGENEOUS THERMAL DECOMPOSITION OF SILANE: EXPERIMENT AND NUMERICAL MODELING

Abstract Experimental and numerical study of aerosol formation under heterogeneous/homogeneous silane thermal decomposition is carried out. Experimental exploration included monitoring of the following parameters during silane decomposition: silane conversion degree and concentrations of disilane and trisilane; aerosol concentration; size and morphology of aerosol particles; number of monohydride SiH and polyhydride (SiH 2 ) n groups in aerosol particles; number of dangling bond active centers in aerosol particles. To explain the experimental results, a numerical model was developed. It covered homogeneous reactions (involving 11 gaseous species), heterogeneous reactions of silicon wall deposition from gaseous species, aerosol formation and aerosol particle wall deposition. The modeling results are in reasonable agreement with the experimental data.

On the pathways of aerosol formation by thermal decomposition of silane

The mechanism of aerosol formation during thermal decomposition of silane is investigated. To this end a simultaneous analysis of gas-phase products of silane decomposition (disilane, trisilane, hydrogen) and the parameters of the forming aerosol particles of amorphous hydrogenated silicon is carried out. The silane loss and gaseous product concentrations are analyzed by mass-spectrometer; particle size and morphology are analyzed by transmission electron microscope. The total amount of bonded hydrogen and the relative amounts of monohydride and polyhydride groups contained in the particles are analyzed by the methods of hydrogen evolution and IR-spectroscopy. It is concluded that during the initial stages of aerosol formation, particles are mainly formed from gaseous products with a stoichiometry Si n H 2n . At these stages the hydrogen in particles is mainly contained as a constituent of polyhydride groups. During later stages the particles are formed from hydrogen-depleted intermediates, and the hydrogen in particles is mainly bound in monohydride groups.

STUDYING OF SILANE THERMAL DECOMPOSITION MECHANISM

The mechanism of silane thermal decomposition is investigated in a flow reactor. The time dependencies of silane consumption and disilane formation were compared with those parameters of solid product (aerosol particles) such as concentration, total hydrogen content in solid product, and fraction of hydrogen contained in solid product as polyhydride groups (SiH2)n. Silane loss and gaseous product formation were analyzed using a mass spectrometer. The hydrogen content in solid product was analyzed by the methods of IR-spectroscopy and hydrogen evolution. Based on a simple kinetic scheme we qualitatively explained the experimental dependencies of silane conversion and disilane formation, the effective activation energy of the decomposition process, and the amount of polyhydride groups in the solid product on reaction time and initial silane concentration.

Control of in vivo transport and toxicity of nanoparticles by tea melanin

Nanoparticles are unfamiliar to researchers in toxicology. Toxicity may be generated simply due to the reduction in size. Compounds that prevent or cure toxic materials may not work on nanoparticles. Furthermore, as there are more and more applications of nanoparticles in drug delivery and in vivo imaging, controlling the transport and toxicity will be primary concerns formedical application of nanoparticles. Gold nanoparticles (GNPs) if injected intraperitoneally intomice can enter hippocampus and induce cognitive impairment. GNPs caused a global imbalance of monoamine levels, specifically affecting the dopaminergic and serotonergic neurons. Pretreatment of tea melanin significantly prevented the deposition of GNPs in mouse brains, especially in the hippocampus. Pretreatment of melanin completely alleviated GNP-induced impairment of cognition. Preadministration of melanin stably maintained monoamines at normal profiles. Melanin completely prevented the invasion of GNPs into the Cornu Ammonis region of the hippocampus shown by coherent anti-Stoke Raman scattering microscopy. Here we show that the administration of tea melanin prevented the accumulation of Au in brain, the imbalance of monoamines, and the impairment of cognition in mice. The current study provides a therapeutic approach to toxicity of nanoparticles and a novel strategy to control the transport of GNP in mouse brain.

Anti-inflammatory Effect from Indomethacin Nanoparticles Inhaled by Male Mice

The respiratory system provides entry for drug nanoparticles to cure systemic diseases. The modern devices that are available on the market of therapeutic aerosol delivery systems have a number of disadvantages. There remains a need for an alternative means that is low cost, convenient, and capable of producing small-sized particles. On the other hand, one-third of the modern drugs are poorly water soluble. Many currently available injectable formulations of such drugs can cause side effects that originate from detergents and other agents used for their solubilization. The aerosol lung administration may by a good way for delivery of the water-insoluble drugs. We present here a new way for the generation of drug nanoparticles suitable for many water insoluble substances based on the evaporation-condensation route. In this paper the indomethacin nanoaerosol formation was studied and its anti-inflammatory effect to the outbred male mice was examined. The evaporation-condensation aerosol generator consisted of a horizontal cylindrical quartz tube with an outer heater. Argon flow was supplied to the inlet and the aerosol was formed at the outlet. The particle mean diameter and number concentration were varied in the ranges 3 to 200 nm and 10(3) to 10(7) cm(-3), respectively. The liquid chromatography and X-ray diffraction methods have shown the nanoparticles consist of the amorphous phase indomethacin. The aerosol lung administration experiments were carried out in the whole-body exposure chamber. Both the lung deposited dose and the particle deposition efficiency were determined as a function of the mean particle diameter for mice being housed into the nose-only exposure chambers. The anti-inflammatory action and side pulmonary effects caused by the inhalation of indomethacin nanoparticles were investigated. It was found that the aerosol administration was much more effective than the peroral treatment. The aerosol route required a therapeutic dose six orders of magnitude less than that for peroral administration.

Chemical composition and bond structure of aerosol particles of amorphous hydrogenated silicon forming from thermal decomposition of silane

Abstract Aerosol particles of amorphous hydrogenated silicon resulting from thermal decomposition of silane were investigated by hydrogen evolution, IR-, EPR-, NMR spectroscopy, and transmission electron microscopy. The experimental data show that aerosol particles contain to a various extent {SiH2}n polymer structures and two types of monohydride groups SiH- “clustered” and “dilute” monohydride groups. The hydrogen atoms of the “clustered” monohydride groups are located close to each other. The “clustered” monohydride groups are inaccessible to the ambient because they are embedded in the amorphous network. The “dilute” monohydride groups are relatively isolated from each other. The majority of “dilute” monohydride groups are open to the ambient. They are located on the surface of preferentially interconnected microchannels and microvoids. Interaction between the “dilute” SiH groups and atmospheric oxygen results in formation of OSiH groups in which hydrogen and oxygen are bonded to a common silicon atom. Evidently, the interaction occurs throw the oxygen reaction with weak bonds associated with “dilute” monohydride groups. There is no interaction between oxygen and both “clustered” SiH groups and {SiH2}n chain because the former are inaccessible to atmospheric oxygen and the latter has presumably no weak bonds in the chains.

Analgesic Effect from Ibuprofen Nanoparticles Inhaled by Male Mice

BACKGROUND Aerosol lung administration is a convenient way to deliver water-insoluble or poorly soluble drugs, provided that small-sized particles are generated. Here, for the outbred male mice, we show that the pulmonary administration of ibuprofen nanoparticles requires a dose that is three to five orders of magnitude less than that for the orally delivered particles at the same analgesic effect. METHOD The aerosol evaporation-condensation generator consisted of a horizontal cylindrical quartz tube with an outer heater. Argon flow was supplied to the inlet and aerosol was formed at the outlet. The particle mean diameter and number concentration varied from 10 to 100 nm and 10(3)-10(7) cm(-)3, respectively. The analgesic action and side pulmonary effects caused by the inhalation of ibuprofen nanoparticles were investigated. RESULTS The chemical composition of aerosol particles was shown to be identical with the maternal drug. Using the nose-only exposure chambers, the mice lung deposition efficiency was evaluated as a function of the particle diameter. CONCLUSIONS The dose-dependent analgesic effect of aerosolized ibuprofen was studied in comparison with the oral treatment. It was found that the dose for aerosol treatment is three to five orders of magnitude less than that required for oral treatment at the same analgesic effect. Accompanying effects were moderate venous hyperemia and some emphysematous signs.

AGGREGATE FORMATION UNDER HOMOGENEOUS SILANE THERMAL DECOMPOSITION

A complete model of aerosol particle formation by thermal decomposition of silane is presented, which includes all steps from aerosol precursor formation in the homogeneous reactions to particle coagulation. The model predicts silane conversion, concentrations of gaseous intermediates (disilane, trisilane, and others), size and concentration of aerosol particles, chemical composition of aerosol particles (number of SiH and SiH2 groups in the particles). Additionally, we report measurements of aggregate fractal dimensions on the basis of electron microscopy micrographs. These data are required to link the chemical kinetic steps of the model with predictions about the particle size. Calculated time dependencies of gaseous concentrations, particle size and concentration, particle chemical composition are in reasonable agreement with the experimental data obtained in the present work as well as in our earlier papers (Onischuk et al., 1997a,b, 1998a). The numerical simulations showed that the relative contribution of vapor and clusters (containing not more than 10 silicon atoms) to the rate of particle growth is in the range of 20–30%. The contribution from the particles containing more than 106 silicon atoms is in the range 70–80%.

Laboratory and field tests of a novel three-stage personal dust sampler for sampling three dust fractions simultaneously

This study designed and calibrated a novel three-stage personal dust sampler for sampling inhalable, thoracic, and respirable dust fractions simultaneously. The sampler has an annular inlet as the first stage for inhalable dust sampling, two impactors in the second and third stages to classify thoracic and respirable dusts, respectively, and a final filter. Laboratory calibration tests using monodisperse liquid and solid particles showed that with 100 ppi (pores per inch) PUF (porous polyurethane foam) substrates and at the flow rate of 3.2 L/min, the sampling efficiency curves of both impactor stages matched with the ISO/CEN/ACGIH thoracic and respirable sampling criteria, respectively. The sampler also agreed with the inhalable criterion for particles smaller than 17 μ m while the deviation increases with increasing particle diameter with a maximum of 28% for 27 μ m particles. It was also found that collection efficiency curve for solid particles was similar to that of liquid particles, indicating that there was no solid particle bounce from the PUF substrates for both impactors. This study also compared inhalable, thoracic, and respirable dust concentrations measured by the present three-stage personal dust samplers with those of the Respicon samplers at three different workplaces. Without using a correction factor of 1.5 for the extrathoracic dusts of the Respicon, field results showed that the present three-stage sampler measured three dust fractions comparable to those of the Respicon samplers. The inhalable dust concentrations of the two samplers differed within 5% while the thoracic and respirable concentration differed by less than 22%.