• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2022-2024
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• 2005

Electrical double-layer capacitor (EDLC) is an electrochemical energy storage device in which electric charges only accumulated by a pure electrostatic attraction force are stored on the electrolyte-electrode interface in a form of double layer and separated by the electrolyte. The composite was prepared by mixing nanosize $TiO_2$ and activated carbon through a means of ultrasonic vibration in ethanol solution for 30 min in various mass ratios of $AC:TiO_2$ to form activated carbone-semiconducting oxide composites. Either 1.0 M $LiClO_4/EC-DEC$ or $Et_4NBF_4$/EC-DEC was used as the electrolyte. It was found that with modification of $TiO_2$, the specific capacitance of activated carbon measured at $1mA/cm^2$ was increased from 40 to 50 F/g. This method is unique in comparison the conventional method because it uses semiconducting TiO2 other than electrochemically active materials such as $RuO_2$. The increase in specific capacitance could be attributed to the decrease in electric polarization, caused by the introduction of $RuO_2$.

• Advances in nano research
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• v.7 no.6
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• pp.379-390
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• 2019

Putting emphasis on the effect of existence of porosity in the functionally graded materials (FGMs) on the dynamic responses of waves scattered in FG nanobeams resulted in implementation of a novel porosity-based homogenization method for FGMs and show its applicability in a wave propagation problem in the presence of axial pre-load for the first time. In the employed porosity-dependent method, the coupling between density and Young's moduli is included to consider for the effective moduli of the FG nanobeam by the means of a more reliable homogenization technique. The beam-type element will be modeled via the classical theory of beams, namely Euler-Bernoulli beam theory. Also, the dynamic form of the principle of virtual work will be extended for such nanobeams to derive the motion equations. Applying the nonlocal constitutive equations of Eringen on the obtained motion equations will be resulted in derivation of the nanobeam's governing equations. Depicted results reveal that the dispersion responses of FG nanobeams will be decreased as the porosity volume fraction is increased which must be noticed by the designers of advanced nanosize devices who are interested in employment of wave dispersion approach in continuous systems for specific goals.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.655-659
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• 2019

Calcium phosphates such as HA (hydroxyapatite), β-TCP (tricalcium phosphate) and biphasic HA/β-TCP, were synthesized by wet chemical precipitation in aqueous solution combined with ball milling process. Nanosize powders of the calcium phosphates were synthesized using Ca(OH)2 and H3PO4. The effects of initial precursor Ca/P ratio (1.30, 1.50 and 1.67), ball milling process and post heat-treatment on the phase evolution behavior of the powders were investigated. The phase of resulting powder was controllable by adjusting the initial Ca/P ratio. HA was the only phase for as-prepared powders in both cases of Ca/P ratios of 1.50 and 1.67. The single HA phase without any noticeable second phase was obtained for the initial Ca/P ratio of 1.67 in the overall heat-treatment range. Pure β-TCP and biphasic calcium phosphate (HA/β-TCP) were synthesized from precursor solutions having Ca/P molar ratios of 1.30 and 1.50, respectively, after having been heat-treated above 700 ℃. The β-TCP phase has appeared on the pre-existing DCPD (dicalcium phosphate dihydrate) and/or HA phase. Dense ceramics having translucency were obtained at a considerably lower sintering temperature. The modified process offered a fast, convenient and economical route for the synthesis of calcium phosphates.

• Steel and Composite Structures
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• v.49 no.3
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• pp.293-306
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• 2023

This article focuses on the study of the buckling behavior of two-dimensional functionally graded (2D-FG) nanosize tubes, including porosity, based on the first shear deformation and higher-order theory of the tube. The nano-scale tube is simulated using the nonlocal gradient strain theory, and the general equations and boundary conditions are derived using Hamilton's principle for the Zhang-Fu's tube model (as a higher-order theory) and Timoshenko beam theory. Finally, the derived equations are solved using a numerical method for both simply-supported and clamped boundary conditions. A parametric study is performed to investigate the effects of different parameters, such as axial and radial FG power indices, porosity parameter, and nonlocal gradient strain parameters, on the buckling behavior of the bi-dimensional functionally graded porous tube. Keywords: Nonlocal strain gradient theory; buckling; Zhang-Fu's tube model; Timoshenko theory; Two-dimensional functionally graded materials; Nanotubes; Higher-order theory.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.187-187
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• 2012

In this report, the plasmonic nanopores of less than 5 nm diameter were fabricated on the apex of the pyramidal cavity array. The metallic pyramidal pit cavity can also utilized as the plasmonic bioreactor, and the fabricated Au or Al metallic nanopore can provide the controllable translocation speed down using the plasmonic optical force. Initially, the SiO2 nanopore on the pyramidal pit cavity were fabricated using conventional microfabrication techniques. Then, the metallic thin film was sputter-deposited, followed by surface modification of the nanometer thick membrane using FESEM, TEM and EPMA. The huge electron intensity of FESEM with ~microsecond scan speed can provide the rapid solid phase surface transformation. However, the moderate electron beam intensity from the normal TEM without high speed scanning can only provide the liquid phase surface modification. After metal deposition, the 100 nm diameter aperture using FIB beam drilling was obtained in order to obtain the uniform nano-aperture. Then, the nanometer size aperture was reduced down to ~50 nm using electron beam surface modification using high speed scanning FESEM. The followed EPMA electron beam exposure without high speed scanning presents the reduction of the nanosize aperture down to 10 nm. During these processes, the widening or the shrinking of the nanometer pore was observed depending upon the electron beam intensity. Finally, using 200 keV TEM, the diameter of the nanopore was successively down from 10 nm down to 1.5 nm.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1379-1389
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• 1999

A new technique for control of size and shape of flame-made particles is Introduced. The characteristic sintering time can be controlled Independently of collision time by heating the particles with irradiation of laser because the sintering time strongly depends on temperature. A coflow oxy-hydrogen diffusion flame burner was used for $SiCl_4$ conversion to silica particle. Nanometer sized aggregates irradiated by a high power CW $CO_2$ laser beam were rapidly heated up to high temperatures and then were sintered to approach volume-equivalent spheres. The sphere collides much slower than the aggregate, which results in reduction of sizes of particles maintaining spherical shape. Light scattering of Ar ion laser and TEM observation using a local sampling device were used to confirm the above effects. When the $CO_2$ laser was irradiated at low position from the burner surface, particle generation due to gas absorption of laser beam occurred and thus scattering intensity increased with $CO_2$ laser power. At high irradiation position, scattering intensity decreased with $CO_2$ laser power and TEM image showed a clear mark of evaporation and recondensation of particles for high $CO_2$ laser power. When the laser was irradiated between the above two positions where small aggregates exist, average size of spherical particles obviously decreased to 58% of those without $CO_2$ laser irradiation with the spherical shape. Even for increased carrier gas flow rate by a factor of three, TEM photograph also revealed considerable reduction of particle size.

• KSBB Journal
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• v.26 no.6
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• pp.505-512
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• 2011

Psolarea corylifolia extract that contains bakuchiol is known to have anti-microbial, anti-inflammatory and anti-scarring effects. In this study, a vesicles such as liposome, niosome, and transfersome were produced to encapsulate P. corylifolia extract and measured their stability and physiochemical property. The skin permeation and partitioning of P. corylifolia extract in the vesicles were elucidated in nude mouse skin by using Franz diffusion cells after topical application for 24 h. After storage at 25, 40, $70^{\circ}C$, and light, the stability of bakuchiol incorporated into the vesicles was maintained for 30 days. The optimal concentration of P. corylifolia extract entrapped into the vesicles was found to be 5~10%. From the physicochemical studies, after storage at 4, 25, and $40^{\circ}C$, the viscosity and particle size of the vesicles remained in 30~80 cP and the nanosize range for 6 months, respectively. From the permeation experiments, niosome showed a higher amount of bakuchiol permeated through the mouse skin compared to liposome and transfersome after 24 h. From these results, niosome and transfersome could be a good bioavailability enhancement system (BAES) for P. corylifolia extract to improve the skin permeation and stability.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2391-2399
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• 2014

Novel dual responsive pectin hydrogels composed from poly(acrylamidoglycolic acid-co-vinylcaprolactam)/Pectin (PAV-PC) and also PAV-PC hydrogels are used as templates for the production of silver nanoparticles. 5-Fluorouracil is an anticancer drug and has been loaded in situ into PAV-PC hydrogels. Structure and morphology characterization of PAV-PC hydrogels were investigated by fourier transform infrared spectroscopy, differential scanning calorimetry, thermo gravimetric analysis, X-ray diffraction studies, scanning electron microscopy and transmission electron microscopy. The results revealed a molecular level dispersion of the drug in PAV-PC hydrogels. In vitro release of 5-fluorouracil from the PAV-PC hydrogels has been carried out in GIT fluids as well as in various temperatures. 5-Fluorouracil released from PAV-PC hydrogels was 50% at pH 1.2, and 85% at pH 7.4 within 24 h. The release profile was characterized with PAV-PC hydrogels and initial burst effect was significantly reduced in two buffer media (1.2 and 7.4), followed by a continuous and controlled release phase, the drug release mechanism from polymer was due to Fickian diffusion. In situ fabrication of silver nanoparticles inside the hydrogel network via the reduction of sodium borohydrate by PAV-PC chains led to hydrogel nanocomposites. The diameter of the nanocomposites was about 50-100 nm, suitable for uptake within the gastrointestinal tract due to their nanosize range and mucoadhesive properties. These nanocomposite PAV-PC hydrogels showed strong antimicrobial activity towards Bacillus subtilis (G+ve) and Escherichia coli (G-ve).

• Journal of Energy Engineering
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• v.18 no.2
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• pp.141-146
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• 2009

In present work, we study the hydrogen storage of MWNT decorated with bimetallic Pt and Pd nanosize catalysts by Thermal Vapor Deposition [TVD]. The size of Pt and Pd particles is controlled as 5nm, 3nm, respectively by TVD. Before hydrogen storage measurement, the sample was heated for 1hr at $200^{\circ}C$ in H2 atmosphere. The Hydrogen sto rage of the sample was performed at room temperature and 33~34atm. The hydrogen storage of this composite showed 3.2wt% at 298K and 34atm, for three times. At 4th cycle, hydrogen storage is decreased to 1.5wt%, owing to the aggregation of bimetallic Pt and Pd nano particles.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1197-1201
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• 2003

Thin film on SiO$_2$ glass was synthesized by a dip-coating method from the ZrO$_2$ sol which had dispersed nanosize Au particle under ambient atmosphere. After heat treatment of the prepared thin film, the characteristics were investigated by X-ray diffraction, UV-VIS spectrometer, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). It was found that ZrO$_2$ thin film with 100 nm thickness was crystallized to tetragonal phase at 50$0^{\circ}C$. The size of dispersed Au particle was 15∼40nm and the film had a smooth surface with a roughness of 0.84 nm. The film showed nonlinearity characteristics with absorption peaks at 630∼670nm visible region because of the plasma resonance of Au metallic particles.