• Bulletin of the Korean Chemical Society
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• v.31 no.7
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• pp.1891-1896
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• 2010

Submicron-sized polymeric colloidal particles can self assemble into 3-dimensional (3D) opal structure which is a useful template for photonic crystal. Narrowly dispersed polymer microspheres can be synthesized by emulsion polymerization in water using water-soluble radical initiator. In this report, we demonstrate a facile and reproducible emulsion polymerization method to prepare various polymeric microspheres within 200 - 400 nm size ranges which can be utilized as colloidal photonic crystal template. By controlling the amount of monomer and surfactant, monodisperse polymer colloids of polystyrene (PS) and acrylates with various sizes were successfully prepared without complicated synthetic procedures. Such polymer colloids self-assembled into 3D opal structure exhibiting bright colors by reflection of visible light. The colloidal particles and the resulting opal structures were rigorously characterized, and the wavelength of the structural color from the colloidal crystal was confirmed to have quantitative relationship with the size of constituting colloidal particles as predicted by Bragg equation. The tunability of the structural color was achieved not only by varying the particle size but also by infiltration of the colloidal crystal with liquids having different refractive indices.

• Bulletin of the Korean Chemical Society
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• v.29 no.8
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• pp.1539-1544
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• 2008

A polymeric micelle, based on the poly(benzyl-L-histidine)-b-poly(ethylene glycol) (polyBz-His-b-PEG) diblock copolymer, was designed as a tumor-specific targeting carrier. The micelles (particle size: 67-80 nm, critical micelle concentration (CMC); 2-3 $\mu$g/mL) were formed from the diafilteration method at pH 7.4, as a result of self-assembly of the polyBz-His block at the core and PEG block on the shell. Removing benzyl (Bz) group from polyBz-His block provided pH-sensitivity of the micellar core; the micelles were physically destabilized in the pH range of pH 7.4-5.5, depending on the content of the His group free from Bz group. The ionization of His group at a slightly acidic pH promoted the deformation of the interior core. These pHdependent physical changes of the micelles provide the mechanism for pH-triggering anticancer drug (e.g., doxorubicin: DOX) release from the micelle in response to the tumor’s extracellular pH range (pH 7.2-6.5).

• Journal of Powder Materials
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• v.18 no.4
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• pp.347-358
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• 2011

Two different schemes were adopted to fabricate ordered macroporous structures with face centered cubic lattice of air spheres. Monodisperse polymeric latex suspension, which was synthesized by emulsifier-free emulsion polymerization, was mixed with metal oxide ceramic nanoparticles, followed by evaporation-induced self-assembly of the mixed hetero-colloidal particles. After calcination, inverse opal was generated during burning out the organic nanospheres. Inverse opals made of silica or iron oxide were fabricated according to this procedure. Other approach, which utilizes ceramic precursors instead of nanoparticles was adopted successfully to prepare ordered macroporous structure of titania with skeleton structures as well as lithium niobate inverted structures. Similarly, two different schemes were utilized to obtain disordered macroporous structures with random arrays of macropores. Disordered macroporous structure made of indium tin oxide (ITO) was obtained by fabricating colloidal glass of polystyrene microspheres with low monodispersity and subsequent infiltration of the ITO nanoparticles followed by heat treatment at high temperature for burning out the organic microspheres. Similar random structure of titania was also fabricated by mixing polystyrene building block particles with titania nanoparticles having large particle size followed by the calcinations of the samples.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.497-502
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• 2005

This study investigated the effects of the substrate and powder content on the fabrication of SiO$_{2}$ photonic crystals by evaporation method. Photonic crystals were self-assembled on quartz, Corning 1737 glass, slide glass, and ITa glass to verify the effects of the wetting angle and surface morphology. The powder contents of the solution were varied from 0.2 to 2.0 wt$\%$. The number of photonic crystal layers increased according to the decrease of wetting angle and surface roughness. The resultant photonic crystals showed the best optical characteristics when the number of photonic crystal layers was within 40 and 50. In addition, the intensity peak of Fabry¡?Perot fringes increased when the wetting angle was large and the particle size was small. Photonic crystals coated on ITO glass showed the highest reflectance peak of 63$\%$ relative intensity.

• Nuclear Engineering and Technology
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• v.34 no.5
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• pp.494-501
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• 2002

Radioactive Corrosion Products (CRUD) which are generated by the neutron activation of general corrosion products at the nuclear power plant are the major source of occupational radiation exposure. Most of the CRUD has a characteristic of showing strong ferrimagnetisms. Along with the new development and production of permanent magnet (rare earth magnet) which generates much stronger magnetic field than the conventional magnet, new type of magnetic filter that can separate CRUD efficiently and eventually reduce radiation exposure of personnel at nuclear power plant is suggested. This separator consists of inner and outer magnet assemblies, coolant channel and container surrounding the outer magnet assembly. The rotational motion of the inner and outer permanent magnet assemblies surrounding the coolant channel by driving motor system produces moving alternating magnetic fields in the coolant channel. The CRUD can be separated from the coolant by the moving alternating magnetic field. This study describes the results of preliminary experiment performed with the different flow rates of coolant and rotation velocities of magnet assemblies. This new magnetic filter shows better performance results of filtering the magnetite at coolant (water). How rates, rotating velocities of magnet assemblies and particle sizes turn out to be very important design parameters.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.127-131
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• 2005

We examined the effect of low temperature heat-treatment on the optical properties of the photonic crystals self-assembled using a monodispersed spherical $SiO_2$ nanoparticle. When the heat treatment temperature increased, the reflectance peak, which is induced by the photonic band gap, moved to a shorter wavelength direction, and the peak intensity of Fabry-Perot fringes also increased. The highest reflectance peak intensity was obtained in the sample heat-treated at $250\~300^{\circ}C$. The heat-treatment reduced the average particle size and the quantity of defects, and increased the packing density of the photonic crystal.

• Journal of Drive and Control
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• v.9 no.2
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• pp.39-45
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• 2012

The NAS 1638 cleanliness classification system was originally developed in 1966 by the US Aircraft Industries of America to both simplify reporting of particle count data and to control the introduction of dirt during the assembly of aircraft fluid systems. The numbers of particles at stated sizes are represented by broad bands where the interval was generally a doubling of contamination. A number of systems have been introduced since this to suit differing requirements. NAS 1638 and AS4059 are used in other industrial sectors such as the Off-shore & Sub-Sea and the Primary Metal Industries. The changes to ISO contamination measurement standards controlled by ISO/TC131/SC6 in 1999 meant that a revision of most of these classification systems was necessary. The body responsible for NAS 1638 decided to withdraw it for new installations and replace it with an update of an existing standard, SAE AS 4059. This paper details the philosophy behind the contamination coding systems, the reasons for the changes to the ISO contamination standards and explains the workings of AS 4059, the replacement for NAS 1638. It goes on to detail the latest changes to this standard.

• Progress in Superconductivity
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• v.12 no.1
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• pp.41-45
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• 2010

Low temperature micro-calorimeters have been employed in the field of high resolution alpha spectrometers. These alpha detectors typically consist of a superconducting or metal absorber and a temperature sensor. The temperature sensor can be a transition edge sensor (TES), a metallic magnetic calorimeter (MMC) or other low temperature detectors for an accurate measurement of temperature change due to an alpha particle absorption. We report a recent study of the heat flow between a replaceable absorber and a temperature sensor. A piece of gold foil in $2.4{\times}2.7{\times}0.03\;mm^3$ is used as an absorber. A $40\;{\mu}m$ diameter Au:Er paramagnetic sensor is attached to another small piece of gold foil in $400{\times}200{\times}30\;{\mu}m^3$ to serve as the temperature sensor. This sensor assembly, Au:Er and gold foil, is placed on a miniature SQUID susceptometer in a gradiometric configuration. The thermal connection between the absorber and the sensor was made with three gold bonding wires. The measured thermal conductance shows a linear dependence to the temperature. The values are in a good agreement with Wiedemann-Franz type thermal conductance of the gold wires.

• Macromolecular Research
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• v.15 no.7
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• pp.623-632
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• 2007

Thermosensitive nanoparticles were prepared via the self-assembly of two different $poly({\varepsilon}-caprolactone)$-based block copolymers of poly(N-isopropylacrylamide)-b-$poly({\varepsilon}-caprolactone)$ (PNPCL) and poly(ethylene glycol)-b-$poly({\varepsilon}-caprolactone)$ (PEGCL). The self-aggregation and thermosensitive behaviors of the mixed nanoparticles were investigated using $^1H-NMR$, turbidimetry, differential scanning microcalorimetry (micro-DSC), dynamic light scattering (DLS), and fluorescence spectroscopy. The copolymer mixtures (mixed nanoparticles, M1-M5, with different PNPCL content) formed nano-sized self-aggregates in an aqueous environment via the intra- and/or intermolecular association of hydrophobic PCL chains. The microscopic investigation of the mixed nanoparticles showed that the critical aggregation concentration (cac), the partition equilibrium constants $(K_v)$ of pyrene, and the aggregation number of PCL chains per one hydrophobic microdomain varied in accordance with the compositions of the mixed nanoparticles. Furthermore, the PNPCL harboring mixed nanoparticles evidenced phase transition behavior, originated by coil to the globule transition of PNiPAAm block upon heating, thereby resulting in the turbidity change, endothermic heat exchange, and particle size reduction upon heating. The drug release tests showed that the formation of the thermosensitive hydrogel layer enhanced the sustained drug release patterns by functioning as an additional diffusion barrier.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.103-110
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• 2004

The major trend in global automotive market is changing drastically in the way that a vehicle FECPS(Front End Cooling Pack System) is designed and manufactured as an assembly part. The system can encompass many functions, be assembled into a vehicle as a module, and reduce the production cost as well as time. The FECPS consists of an impact beam, an aluminum condenser and a radiator, a carrier and a cooling fan with a BLDC motor. In order to predict the performance of a FECPS accurately, it is essential to properly model the air flow field through various heat exchangers, such as a condenser or a radiator. In this study, the flow field of the system is measured by a PIV(Particle Image Velocimetry) system. The result is compared with that measured with multi-channel anemometer.