• Journal of Korean Society for Atmospheric Environment
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• v.11 no.3
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• pp.291-298
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• 1995

An intensive field study was carried out during Aug. 1993 in Seoul to study the characteristics of summertime visibility and diurnal trend of ionic composition of ambient particles. A transmissometer, nephelometer with heated and unheated inlets, PM3 fine particle sampler, and cascade impactor were used to measure optical and particle properties of ambient air. During this study period, a weak smog episode has occurred. Light scattering by particles is the most dominant factor on total light extinction. The effect of light absorption by particles in Seoul is much higher than other major cities in U.S.A. throughout the summer and fall with relatively constant values. The effect of water on $b_{sp}$ was small during the period. The particle size distribution shows a typical bimodal one. Sulfate, ammonium, chloride, and nitrate are the major chemical species in fine fraction aerosols, about 30% of toral mass concentration. Concentraion of sulfate is higher during the daytime while those of nitrate and chloride are higher during the nighttime. Ammonium concentration is constant through the daytime.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.257-260
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• 2015

Light extinction characteristics of soot particles in ethylene and propane inverse diffusion flames have been experimentally investigated. The measured data suggested that the refractive index of soot particles varies with light wavelength due to PAH contents existing during the soot growth process. The results showed that the scattering effect is less important as the size of secondary particles rarely affects the optical properties of the soot even when the size is large enough to deviate from Rayleigh assumptions.

• Polymer(Korea)
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• v.39 no.3
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• pp.370-381
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• 2015

In the system of poly(vinyl alcohol) (PVA)/dimethyl sulfoxide, the refractive index of polymer was very well matched to that of solvent and thus its scattered intensity could be minimized. After adding small amount of polystyrene latex particle (nominal diameter 200 nm), diffusion behavior of only probe particle was investigated against the concentration of polymer matrix by means of dynamic light scattering. The polymer concentration dependence of its reduced diffusion coefficient was able to be analysed with the stretched exponential function of the reduced concentration $C[{\eta}]$. In very dilute concentration regime, the depletion layer kept constant but at the early semi-dilute regime of $1{\leq}C[{\eta}]{\leq}2.5$, the concentration-dependent exponent of depletion layer ${\delta}$ was appeared to be -0.8 which was very close to theoretical one of -0.85. However it was also observed at the higher concentration that its layer thickness decreased more abruptly than theoretical expectation and this phenomenon was ascribed to Oosawa type attractive interaction between adjacent latex particles.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.9
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• pp.737-744
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• 2012

The finite volume method for radiation is applied for the analysis of radiative base heating by SE and PE of the aircraft exhaust plume. The exhaust plume is considered as an absorbing, emitting, and scattering medium, while the base plane is assumed to be cold and black. The radiative properties of non-gray gases are obtained through the WSGGM, and the particle is modelled as spheres. The present method is validated by comparing the results with those of the backward Monte-Carlo method and then the radiative base heating characteristics are analyzed by changing such various parameters as particle concentration, temperature, and scattering phase function. The results show that the radiative heat flux coming into the base plane decreases with altitude and distance, but it increases as the particle temperature increases. The forward scattering of particles increases PE while it decreases SE.

• Polymer(Korea)
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• v.36 no.5
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• pp.628-636
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• 2012

The polymer concentration dependence of depletion layer was investigated by means of dynamic light scattering after the very small amount of polystyrene spherical latex particles was added into the matrix solution of poly(vinyl alcohol)(PVA)/dimethyl sulfoxide. At the dilute regime, the magnitude of depletion layer kept constant at the level of $63{\pm}3%$ of the radius of gyration of the corresponding PVA chain. Next, at the early semi-dilute regime of $1.5{\leq}C[{\eta}]{\leq}3$, polymer concentration dependence of the layer thickness ${\delta}$ was obtained as ${\delta}{\sim}C^{-0.8}$, and this experimental value was very close to theoretical one of -0.75. However it was observed above $C[{\eta}]$ >3 that its thickness decreased abruptly, and this was ascribed to aggregation effect of latex particles which was driven by Oosawa type attractive interaction.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.2966-2970
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• 2012

Fullerene/polystyrene ($C_{60}$/PS) nano particle was prepared by using emulsion polymerization. Styrene and fullerene were emulsified in aqueous media in the presence of poly(N-vinyl pyridine) as an emulsion stabilizer, and polymerization was initiated by water soluble radical initiator, potassium persulfate. The obtained nano particles have an average diameter in the range of 400-500 nm. The fullerene contents in the nano particle can be controlled up to 15 wt % by varying the feed ratio, which was confirmed by themogravimetric analysis (TGA) and elemental analysis (EA). The structure and morphologies of the $C_{60}$/PS nano particles were examined by various analytical techniques such as dynamic light scattering (DLS), scanning electron microscope (SEM), transmission electron microscope (TEM), electron diffraction (ED) pattern, X-ray powder diffraction (XRD), and UV spectroscopy. Unlike conventional $C_{60}$/PS particles initiated by organic free radical initiators, in which the fullerene is copolymerized forming a covalent bond with styrene monomer, the prepared $C_{60}$/PS nano particles contain pristine fullerene as secondary particles homogeneously distributed in the polystyrene matrix.

• Asian Journal of Atmospheric Environment
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• v.4 no.3
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• pp.115-140
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• 2010

Great concerns about atmospheric aerosols are attributed to their multiple roles to atmospheric processes. For example, atmospheric aerosols influence global climate, directly by scattering or absorbing solar radiations and indirectly by serving as cloud condensation nuclei. They also have a significant impact on human health and visibility. Many of these effects depend on the size and composition of atmospheric aerosols, and thus detailed information on the physicochemical properties and the distribution of airborne particles is critical to accurately predict their impact on the Earth's climate as well as human health. A single particle analysis technique, named low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA) that can determine the concentration of low-Z elements such as carbon, nitrogen and oxygen in a microscopic volume has been developed. The capability of quantitative analysis of low-Z elements in individual particle allows the characterization of especially important atmospheric particles such as sulfates, nitrates, ammonium, and carbonaceous particles. Furthermore, the diversity and the complicated heterogeneity of atmospheric particles in chemical compositions can be investigated in detail. In this review, the development and methodology of low-Z particle EPMA for the analysis of atmospheric aerosols are introduced. Also, its typical applications for the characterization of various atmospheric particles, i.e., on the chemical compositions, morphologies, the size segregated distributions, and the origins of Asian dust, urban aerosols, indoor aerosols in underground subway station, and Arctic aerosols, are illustrated.

• Journal of Powder Materials
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• v.24 no.3
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• pp.216-222
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• 2017

Synthesized monocrystalline nanodiamond (nD) particles are heat-treated at various temperatures to produce highly structured diamond crystals. The heat-treated nDs show different weight loss ratios during thermogravimetric analysis. The crystallinities of the heat-treated nDs are analyzed using Raman spectroscopy. The average particle sizes of the heat-treated nDs are measured by a dynamic light scattering (DLS) system and direct imaging observation methods. Moreover, individual dispersion behaviors of the heat-treated nD particles are investigated based on ultrasonic dispersion methods. The average particle sizes of the dispersed nDs according to the two different measurement methods show very similar size distributions. Thus, it is possible to produce highly crystallized nD powder particles by a heat-treatment process, and the nD particles are relatively easy to disperse individually without any dispersant. The heat-treated nDs can lead to potential applications such as in nanocomposites, quantum dots, and biomedical materials.

• Bulletin of the Korean Chemical Society
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• v.30 no.1
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• pp.129-132
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• 2009

Monodisperse ZnS colloidal particles with precisely specified diameters over a broad size range were synthesized by controlled aggregation. Sub-10nm ZnS seed crystals were first nucleated at ambient temperature and then grown at an elevated temperature, which produced large polydisperse colloidal particles. Subsequent rapid thermal quenching and heating processes induced a number of secondary nucleations in addition to growing the large polydisperse microparticles which were finally removed by centrifugation and discarded at the completion of the reaction. The secondary nuclei were then aggregated further at elevated temperatures, resulting in colloidal particles which exhibited a nearly monodisperse size distribution. Particle diameters were controlled over a wide size range from 50 nm to 1 μm. Mie simulations of the experiment extinction spectra determined that the volume fraction of the ZnS is 0.66 in an aggregated colloidal particle and the colloidal particle effective refractive index is approximately 2.0 at 590 nm in water. The surface of the colloidal particles was subsequently coated with silica to produce ZnS@silica core-shell particles.

• Transactions on Electrical and Electronic Materials
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• v.7 no.3
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• pp.112-117
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• 2006

In this paper we present that the effects of polymer adsorption on stabilities and CMP performance of ceria abrasive particles. Characterization of ceria abrasive particles in the presence of poly(vinyl pyrrolidone) (PVP) was performed by the measurements of adsorbed amounts of PVP, average sizes, and the back scattering intensities of the ceria abrasive particles as functions of PVP molecular weight and PVP concentration. The ceria abrasive particles in the presence of PVP were used to polish $SiO_2\;and\;Si_3N_4$ films deposited on Si wafers in order to understand the effect of PVP adsorption on chemical mechanical polishing (CMP) performance, together with ceria abrasive particles without PVP. Adsorption of PVP on the ceria abrasive particles enhanced the stability of ceria abrasive particles due to steric stabilization of the thick adsorbed layer of PVP. Removal rates of the deposited $SiO_2\;and\;Si_3N_4$ films by the ceria abrasive particles in the presence of PVP were much lower than those in the absence of PVP and their magnitudes were decreased with an increase in the concentration of free PVP chains in the dispersion media. This suggests that the CMP performance in the presence of PVP could be mainly controlled by the hydrodynamic interactions between the adsorbed PVP chains and the free ones. Moreover, the molecular weight dependence of PVP on the removal rates of the deposited films was hardly observed. On the other hand, high removal rate selectivity between the deposited films in the presence of PVP was not observed.