• 한국재료학회지
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• 제22권6호
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• pp.298-302
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• 2012

Fe/$SiO_2$ core-shell type composite nanoparticles have been synthesized using a reverse micelle process combined with metal alkoxide hydrolysis and condensation. Nano-sized $SiO_2$ composite particles with a core-shell structure were prepared by arrested precipitation of Fe clusters in reverse micelles, followed by hydrolysis and condensation of organometallic precursors in micro-emulsion matrices. Microstructural and chemical analyses of Fe/$SiO_2$ core-shell type composite nanoparticles were carried out by TEM and EDS. The size of the particles and the thickness of the coating could be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of TEOS within the micro-emulsion. The water/surfactant molar ratio influenced the Fe particle distribution of the core-shell composite particles, and the distribution of Fe particles was broadened as R increased. The particle size of Fe increased linearly with increasing $FeNO_3$ solution concentration. The average size of the cluster was found to depend on the micelle size, the nature of the solvent, and the concentration of the reagent. The average size of synthesized Fe/$SiO_2$ core-shell type composite nanoparticles was in a range of 10-30 nm and Fe particles were 1.5-7 nm in size. The effects of synthesis parameters, such as the molar ratio of water to TEOS and the molar ratio of water to surfactant, are discussed.

• Bulletin of the Korean Chemical Society
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• 제22권5호
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• pp.467-475
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• 2001

A triblock copolymer based on $poly(\varepsilon-caprolactone)$ (PCL) as the hydrophobic part and poly(ethylene glycol) (PEG) as the hydrophilic portion was synthesized by a ring-opening mechanism of ${\varepsilon}-caprolactone$ with PEG containing a hydroxyl group at bot h ends as an initiator. The synthesized block copolymers of PCL/PEG/PCL (CEC) were confirmed and characterized using various analysis equipment such as 1H NMR, DSC, FT-IR, and WAXD. Core-shell type nanoparticles of CEC triblock copolymers were prepared using a dialysis technique to estimate their potential as a colloidal drug carrier using a hydrophobic drug. From the results of particle size analysis and transmission electron microscopy, the particle size of CEC core-shell type nanoparticles was determined to be about 20-60 nm with a spherical shape. Since CEC block copolymer nanoparticles have a core-shell type micellar structure and small particle size similar to polymeric micelles, CEC block copolymer can self-associate at certain concentrations and the critical association concentration (CAC) was able to be determined by fluorescence probe techniques. The CAC values of the CEC block copolymers were dependent on the PCL block length. In addition, drug loading contents were dependent on the PCL block length: the larger the PCL block length, the higher the drug loading content. Drug release from CEC core-shell type nanoparticles showed an initial burst release for the first 12 hrs followed by pseudo-zero order release kinetics for 2 or 3 days. CEC-2 block copolymer core-shell type nanoparticles were degraded very slowly, suggesting that the drug release kinetics were governed by a diffusion mechanism rather than a degradation mechanism irrelevant to the CEC block copolymer composition.

• Korean Chemical Engineering Research
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• 제57권1호
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• pp.111-117
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• 2019

기상으로 전달된 Ti 전구체가 열 플라즈마에서 고순도의 결정질 코어-$TiO_2$로 합성됨과 동시에 기판에 바로 증착시킬 수 있는 공정을 제시한다. 제조된 코어-$TiO_2$는 외부에 노출되지 않는 상태에서 원자층증착법(Atomic Layer Deposition, ALD)에 의하여 $Al_2O_3$로 코팅된다. 코어-$TiO_2$와 코팅된 쉘-$Al_2O_3$의 형태학적 특징은 transmission electron microscope (TEM) 및 transmission electron microscope - energy dispersive spectroscopy (TEM-EDS)를 통해 분석하였다. 제조된 코어-$TiO_2$/쉘-$Al_2O_3$ 나노입자의 전기적 특성은 염료감응 태양전지(dye-sensitized solar cell, DSSC)의 작동전극에 적용하여 평가하였다. Dynamic light scattering system (DLS), scanning electron microscope (SEM), X-ray Diffraction (XRD)을 통하여 코어-$TiO_2$의 평균입도, 성장속도 및 결정구조의 무게분율을 분석한 결과, 평균입도는 17.1 nm, 코어박막의 두께는 $20.1{\mu}m$이고 주 결정구조가 Anatase로 증착된 코어-$TiO_2$/쉘-$Al_2O_3$ 나노입자를 적용한 DSSC가 기존의 페이스트 방식으로 제작한 DSSC보다 더 높은 광효율을 보여준다. 기존의 페이스트방식을 활용한 DSSC의 에너지변환효율 4.99%에 비하여 선택적으로 조절된 코어-$TiO_2$/쉘-$Al_2O_3$ 나노입자를 작동전극으로 사용한 경우가 6.28%로 26.1% 더 높은 광효율을 보여준다.

• 한국재료학회지
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• 제15권12호
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• pp.751-755
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• 2005

Fibrous $Al_2O_3-(m-ZrO_2)/t-ZrO_2$ composites having core/shell structure were fabricated by multi-extrusion process. The effect o volume fraction between core ($Al_2O_3-(m-ZrO_2)$) and shell ($t-ZrO_2$ was investigated to understand the relationship between microstructure and material properites, in which the volume fractions of core and shell were varied as 40:60, 50:50 and 60:40. The material properties o hardness and bending strength were increased as the volume fraction of core was increased, and their maximum values were about 1320 Hv and 750MPa, respectively. However, as the volume fraction of core increased, the values of relative density and fracture toughness were decreased from 97.1 to $96.5\%$ and from $6.5MPa{\cdot}m^{1/2}$ to $5.7MPa{\cdot}m^{1/2}$, respectively.

• 한국세라믹학회지
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• 제45권11호
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• pp.750-754
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• 2008

The artificial aggregates with dense surface layer (shell) was fabricated and the dependence of water emission rate upon the shell structures was studied. The EAF dust containing many flux components and waste white clay with ignition loss of above 48% were used as for liquid phase and gas forming agents during a sintering process respectively. In addition, the shell structure was modified with various processes and the modification effect on water emission rate was analyzed. The pores under $10{\mu}m$ were found in the sintered artificial light aggregates and disappeared by incorporating to a bigger pore during re-sintering. The water emission rate in an initial step depended on a void content of aggregates filled in a bottle rather than a shell structure. But, after 7 days where the water emission of the aggregate with a shell is above 40%, the shell of aggregates suppressed the water emission. The core of aggregates was exposed and most shell was lost when crushed to smaller size so, the ability for suppressing water emission of the crushed aggregates decreased. The activation energy for the water emission was $3.46{\pm}0.25{\times}10^{-1}$J/mol for the most specimens showing that the activation energy is irrelevant to the pore size distribution and shell structure.

• Steel and Composite Structures
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• 제32권2호
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• pp.225-237
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• 2019

In this research, the dynamic stability and nonlinear vibration behavior of a smart rotating sandwich cylindrical shell is studied. The core of the structure is a functionally graded material (FGM) which is integrated by functionally graded piezoelectric material (FGPM) layers subjected to electric field. The piezoelectric layers at the inner and outer surfaces used as actuator and sensor, respectively. By applying the energy method and Hamilton's principle, the governing equations of sandwich cylindrical shell derived based on first-order shear deformation theory (FSDT). The Galerkin method is used to discriminate the motion equations and the equations are converted to the form of the ordinary differential equations in terms of time. The perturbation method is employed to find the relation between nonlinear frequency and the amplitude of vibration. The main objective of this research is to determine the nonlinear frequencies and nonlinear vibration control by using sensor and actuator layers. The effects of geometrical parameters, power law index of core, sensor and actuator layers, angular velocity and scale transformation parameter on nonlinear frequency-amplitude response diagram and dynamic stability of sandwich cylindrical shell are investigated. The results of this research can be used to design and vibration control of rotating systems in various industries such as aircraft, biomechanics and automobile manufacturing.

• 한국표면공학회지
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• 제51권6호
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• pp.365-371
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• 2018

1D core-shell nanostructures have attracted great attention due to their enhanced physical and chemical properties. Specifically, oriented single-crystalline $TiO_2$ nanorods or nanowires on a transparent conductive substrate would be more desirable as the building core backbone. However, a facile approach to produce such structure-based hybrids is highly demanded. In this study, a three-step hydrothermal method was developed to grow NiMn-layered double hydroxide-decorated $TiO_2$/carbon core-shell nanorod arrays on transparent conductive fluorine-doped tin oxide (FTO) substrates. XRD, SEM, TEM, XPS and Raman were used to analyze the obtained samples. The in-situ fabricated hybrid nanostructured materials are expected to be applicable for photoelectrode working in water splitting.

• 전기학회논문지
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• 제61권1호
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• pp.85-88
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• 2012

DSCs are based on a dye-adsorbed porous $TiO_2$ layer as a photo electrode [1]. Under the illumination, dye molecules are excited and electrons are produced. The injected electrons in the conduction band of $TiO_2$ may recombine with the electrolyte. To obtain high performance DSCs, it is essential to retard the recombination. The charge recombination can be reduced by forming core-shell structure. In this work, we investigated the core-shell structure with $Al_2O_3$ and MgO coating layer on the porous $TiO_2$ layer. We confirmed the photovoltaic properties by I-V characteristics. The current and the efficiency was improved. In addition to, Through decrease in the width of EIS arc, which is the sum of the interfacial charge transfer resistances of both electrodes, we can be indicated that the block effect.

• 한국분말재료학회지
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• 제23권6호
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• pp.409-413
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• 2016

Electrical wire explosion in liquid media is a promising method for producing metallic nanopowders. It is possible to obtain high-purity metallic nanoparticles and uniform-sized nanopowder with excellent dispersion stability using this electrical wire explosion method. In this study, Ni-Fe alloy nanopowders with core-shell structures are fabricated via the electrical explosion of Ni-Fe alloy wires 0.1 mm in diameter and 20 mm in length in de-ionized water. The size and shape of the powders are investigated by field-emission scanning electron microscopy, transmission electron microscopy, and laser particle size analysis. Phase analysis and grain size determination are conducted by X-ray diffraction. The result indicate that a core-shell structured Ni-Fe nanopowder is synthesized with an average particle size of approximately 28 nm, and nanosized Ni core particles are encapsulated by an Fe nanolayer.

• Macromolecular Research
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• 제17권4호
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• pp.265-270
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• 2009

Noble thermosensitive nanoparticles, based on a PNIPAAm-co-AA core and a chitosan shell structure, were designed and synthesized for the controlled release of the loaded drug. PNIPAAm nanoparticles containing a carboxylic group on their surface were synthesized using emulsion polymerization. The carboxylic groups were conjugated with the amino group of a low molecular weight, water soluble chitosan. The particle size of the synthesized nanoparticles was decreased from 380 to 25 nm as the temperature of the dispersed medium was increased. Chitosan-conjugated nanoparticles with $2{\sim}5$ wt% MBA, a crosslinking monomer, induced a stable aqueous dispersion at a concentration of 1mg/1mL. The chitosan-conjugated nanoparticles showed thermo sensitive behaviors such as LCST and size shrinkage that were affected by the PNIPAAm core and induced some particle aggregation around LCST, which was not shown in the NIPAAm-co-AA nanoparticles. These chitosan-conjugated nanoparticles are also expected to be more biocompatible than the PNIPAAm core itself through the chitosan shell structures.