Don Keun Lee

FTIR and UV-vis spectroscopy studies of Langmuir-Blodgett films of stearic acid/γ-Fe2O3 nanoparticles

Abstract Iron oxide γ -Fe 2 O 3 nanoparticles were synthesized in aqueous solutions and the equilibrium pressure–area isotherms of the Langmuir layers of stearic acid/ γ -Fe 2 O 3 nanoparticle complexes at the air–water interface were studied. In comparison to a pure water subphase, the surface pressure versus the specific area isotherm of the stearic acid was significantly expanded in the presence of the iron oxide nanoparticles in the subphase indicating the existence of interactions between the stearic acid monolayer and the iron oxide nanoparticles. Stearic acid/ γ -Fe 2 O 3 nanoparticle complex monolayers were transferred onto ZnSe and quartz plate substrates from the air–water interface using the Langmuir–Blodgett (LB) technique and the LB films were characterized with FTIR and UV-vis spectroscopy. From the FTIR studies it was observed that complexation between γ -Fe 2 O 3 nanoparticles and stearic acid occurred by electrostatic interactions between the carboxylate ions of stearate and the nanoparticle surface. Using UV-vis spectroscopy, the optical absorbance increased linearly with the number of complex LB layers, which indicated that the multilayer complex LB films were deposited uniformly.

Peripheral 4-1BB Signaling Negatively Regulates NK Cell Development through IFN-γ

Stimulation of 4-1BB (CD137) was shown to produce strong anticancer effects in vivo. In contrast, 4-1BB–deficient (4-1BB−/−) B6 mice are remarkably resistant to tumor growth. We set out to determine the mechanisms involved in these seemingly contradictory observations. We found that the therapeutic effects of 4-1BB triggering were mainly dependent on CD8+ T cells and partially on NK cells, whereas CD8+ T and NK cells were equally needed to suppress tumor growth in 4-1BB−/− mice. Cellular analysis showed that the frequency and number of NK cells in the spleen and bone marrow were decreased by 4-1BB triggering but were increased in the absence of 4-1BB signaling in tumor-challenged mice. The 4-1BB–mediated downregulation of NK cell development was primarily dependent on IFN-γ, which was produced by peripheral CD8+ T and NK cells. The suppression of NK cell development by 4-1BB–mediated IFN-γ production occurred in the bone marrow. As 4-1BB signaling increased in the periphery, more CD8+ T cells but fewer NK cells contributed to the antitumor immunity. As 4-1BB signaling decreased, more NK cells participated in the antitumor immunity. We conclude that 4-1BB signaling results in a shift of the dominant type of immune cell in antitumor immunity from the innate NK cell to the adaptive CD8+ T cell and that the level of IFN-γ is critical for this 4-1BB–mediated shift.

Synthesis and characterization of crystalline FeCo nanoparticles.

The monodispersed FeCo nanoparticles were synthesized with borohydride as a reducing agent by coprecipitation method in aqueous solution. The composition and the size of FeCo nanoparticle was controlled by fitting the molar ratio of starting material, the reaction time and the falling rate. To prepare the crystallized nanoparticles, the amorphous FeCo nanoparticles were annealed at the different temperatures for 1 hr, respectively. The size of the crystalline FeCo nanoparticles was controlled in order to maintain the uniform size of 20 nm. The as-annealed FeCo alloy could get the highest Ms value of the powder which has been ever synthesized by coprecipitation or other chemical method. The size- and shape-controlled crystalline FeCo nanoparticles can be applied for spring magnet in order to get exchange coupling effect.

Kinetics of Decolorization of Spironaphthooxazine-Doped Photochromic Polymer Films

Photochromic polymeric films were prepared by doping photochromic dye spironaphthooxazine into polymer resin gels such as polyurethane, vinyl copolymer, and copolymer of vinyl and nitorocellulose at different concentrations. All of the composite films show normal photochromism. The kinetics of the photochromism/decoloration in the films were quantified by fitting biexponential equations to their photochromic decay curves after irradiation. It was observed that the decoration process is faster in vinyl copolymer than that in the copolymer of vinyl and nitrocellulose and is the slowest in the case of polyurethane. The decoloration mechanisms of spironaphthooxazine in those polymeric matrixes have been discussed.

A Study of Exchange-Coupling Effect on Nd2Fe14B / α-Fe Forming Core/Shell Shape

We report the core/shell type as the interesting one of the various techniques to prepare exchange-coupled permanent magnet. In this study, the exchange-coupled Nd2Fe14B/α-Fe was prepared by high energy ball mill process and chemical reduction. Nd15Fe77B8 powder prepared by high energy ball mill process was coated with α-Fe nanoparticle by chemical reduction. α-Fe nanoparticle on the ball milled Nd15Fe77B8 was synthesized by chemical reduction with borohydride as a reducing agent in aqueous solution. After annealing, Nd2Fe14B/α-Fe forming core/shell shape has exchange-coupling effect and was identified by using XRD, FE-SEM, VSM, TMA and EDX.

Preparation of Water Dispersed Indium Tin Oxide Sol Solution

Indium tin oxide (ITO) nanoparticles with In/Sn = 9:1 (at.%) were synthesized by chemical coprecipitation method in an aqueous solution. The coprecipitate prepared at room temperature showed the crystal structure of indium oxide in X-ray diffraction when it was annealed at the temperature above 300°C under air atmosphere. Reduction process was accomplished to improve the electrical property of ITO powder. Green ITO powder with particle sizes in the range of 20–30 nm was well dispersed by an addition of polyvinylpyrrolidone in an aqueous solution. The dispersibility of ITO sol solution was studied at different conditions by using ζ-potential analyzer. Transmission electron microsopy (TEM) and energy dispersive X-ray spectrometer (EDS) were used to characterize morphology and composition of ITO nanoparticles.

FABRICATION OF EXCHANGE COUPLED HARD/SOFT NANOCOMPOSITE MAGNET AND THEIR CHARACTERIZATION

Monodispersed α-Fe nanoparticles were synthesized under an argon atmosphere via thermal decomposition of Fe2+-oleate2. Nd–Fe–B ultrafine amorphous alloy particles were prepared by reaction of metal ions with borohydride in aqueous solution. Exchange coupled Nd2Fe14B/α-Fe nanocomposite magnets have been prepared by self-assembly using surfactant. The crystal structure of the synthesized nanoparticles was identified by using X-ray powder diffraction (XRD). The size and shape of nanoparticles were obtained by TEM. Thermogravimetry using a microbalance with magnetic field gradient positioned below the sample was used for the measurement of a thermomagnetic analysis (TMA) curve showing the downward magnetic force versus temperature.

SYNTHESIS OF MAGNETITE AND COBALT FERRITE NANOPARTICLES

Fe3O4 and CoFe2O4 magnetic nanoparticles have been synthesized successfully in aqueous solution and coated with oleic acid. The solid and organic solution of the synthesized nanoparticles was obtained. Self-assembled monolayer films were formed using organic solution of these nanoparticles. Both of the two nanoparticles are spherical and have narrow size distributions. The crystal sizes determined by Debye-Scherre equation with XRD data were found close to the particle sizes calculated from TEM images, and this indicates that the synthesized nanoparticles are nanocrystalline. The superparamagnetic behavior of the nanoparticles was documented by the hysteresis loop measured at 300 K.

Preparation and Antibiotic Property of Ag-SiO2 Nanoparticle

Silica particle was deposited with Ag nanoparticles to achieve hybrid structure. First, silica nanoparticles were synthesized according to the well-known Stöber method by hydrolysis and condensation of TEOS in a mixture of ethanol with water, using ammonia as catalyst to initiate the reaction. These SiO2 nanoparticles were dried at 100°C. We measured the size of these nanoparticles with transmission electron microscopy (TEM). Second, Ag-SiO2 nanoparticles were synthesized by reaction with AgNO3 and SiO2 nanoparticles at room temperature for 12 hrs. Results show silica nanoparticles of about 110 nm size deposited with Ag nanoparticles. Ag-SiO2 nanoparticles were investigated with TEM images, energy dispersive X-ray analysis (EDX) spectrum. The antibiotic property was examined with disk plate method.

New Synthetic Method of Magnetite Nanocrystallites Using ?-Irradiation

A new method,γ-irradiation, has been developed to prepare nanocrystalline metal, alloys, metal oxide, and composites. The reactions ofγ-irradiation on a rod type FeOOH in the presence of isopropanol and water have been investigated. In the initial stage of theγ-irradiation, FeOOH was turned into magnetite. With the continuedγ-irradiation(over 50000 Gy), FeOOH disappeared and the product was a single phase of magnetite. XRD, SAD, LRTEM and HRTEM were used to characterize the structure and to determine their morphology, respectively. The VSM spectrum was obtained to study magnetic properties of the products.