Hoy Yul Park

Preparation of Porous Hydroxyapatite Scaffolds for Bone Tissue Engineering

Porous hydroxyapatite (HAp) scaffolds were successfully prepared by using the HAp slurry based on the replication of polymer sponge substrate. The effect of HAp content in slurry on the pore morphology and size, and density, porosity, and mechanical strength of porous scaffolds was investigated. The scaffolds with average pore sizes ranging from 200 to 400 µm had an open, relatively uniform, and interconnected porous structure. As the HAp content increased, the porosity of scaffold decreased while the density increased. These phenomena were attributed to the fact that the pores became interconnected with more dense and thicker pore walls with increasing HAp content in slurry. The results suggest that the density, porosity, and compressive strength of the porous HAp scaffold were significantly affected by the content of the HAp powder in the slurry.

Properties of Nano-Hybrid Sol-Gel Coating Films Synthesized with Colloidal Silica and Organoalkoxy Silanes

Three kinds of colloidal silica (CS)/silane sol were prepared. Sols are involved with the kinds of silane with different organic group. Methyltrimethoxysilane (MTMS) has the three methoxy groups and a methyl group. γ-Glycidoxypropyltrimethoxysilane (GTMS) has the three methoxy groups and a bulky epoxy group. GTMS was added to two sols with different amount. When sol reacted for 10 days, viscosity increased dramatically. Trasnmittance of sols reacted for 10 days decreased rapidly, too. It indicated the stability of sol degraded. Sol-gel coating films were formed on glass substrate using spin coating procedure with reaction time for 10 days. Coating films were flat and transparent without cracking. CS/MTMS coating films showed high contact angle. When large amount of GTMS was added, contact angle decreased due to its epoxy group. No thermal degradation of CS/MTMS coating film occurred up to 600 oC. CS/MTMS/GTMS coating film degraded at 400 oC for decomposition of epoxy group which has long organic chain which easily degraded by the thermal shock.

Properties of Nano-Hybrid Sol-Gel Materials Synthesized from Colloidal Silica-Silane Containing Epoxy Silane

Three kinds of colloidal silica (CS)/silane sol solutions were synthesized in variation with parameters such as different acidity and reaction time. Sol solutions were prepared from HSA CS/ methyltrimethoxysilane (MTMS), LS CS/MTMS and LS CS/MTMS/γ -Glycidoxypropyltri methoxysilane (ES) solutions. In order to understand their physical and chemical properties, sol-gel coating films were fabricated on glass. Coating films on glass, obtained from LS/MTMS sol, had high contact angle, also, much enhanced flat surface in the case of LS/MTMS sol was observed in comparison with HSA/ MTMS sol. From all sol-gel solutions, seasoning effect of for enhancing properties of sol-gel coating layer on glass was observed while such sol-gel solutions were left for 7days. In initial stage of sol-gel reaction, all most of sol solutions used in this work seem to be unstable, formation of coating films was a little hazy and rough. However, improved coating films as observed in 4days later. LS/MTMS/ES sol solutions were synthesized with ES, adding to LS/MTMS sol. Contact angle of LS/MTMS/ES sol-gel coating films decreased, since ES played a role in forming hydrophilic hydroxyl sol. The elastic portion of coating films prepared from LS/MTMS/ES sol increased with addition of ES, but thermal stability decreased a little.

Hydrothermal Syntheses of Nickel Nanosheets and Their Morphology

Nanocrystalline nickel powders were prepared by chemical reduction of nickel chloride hydrate with different surfactant at moderate temperature in a pressurized vessel. Nickel nanosheets were generated successfully through reducing the nickel ion complexes, formed by sodium tartrate, at alkaline condition by hydrazine hydrate. The nanosheets and nanowires were characterized by the means of an X-ray diffractomer (XRD), a field emission scanning electron microscopy (FESEM), an energy dispersive X-ray spectrometer (EDS) and a high sensitive magnetometer (HSM).

Direct photofabrication of various surface structures in photosensitive and transparent hybrid materials using organically modified silica nanoparticles and oligosiloxanes

Hybrid materials composed of organically modified silica nanoparticles and oligosiloxanes exhibited homogeneous dispersion without any phase separation or aggregation and good solution processability. These hybrid materials exhibited good solubility of photoinitiator and high transmittance of above 90% in visible wavelength ranges. In particular, the materials showed high photocurability, with degrees of conversion under UV exposure above 90%. With high photosensitivity, the hybrid materials were used for direct photopatterning without the developing process used in the photomask method. The various optical surface structures on a micrometer scale were easily fabricated in the hybrid films upon UV exposure, and the samples exhibited good root-mean-square (RMS) roughness of around 1 nm.

Synthesis and Characterization of Gd2O3 Doped CeO2 Nanopowders by a Glycothermal Process

Gd2O3 doped CeO2 nanopowders were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous ammonium hydroxide. Spherical shape Gd2O3 doped CeO2 nanopowders were obtained By a reaction at the temperature range of 200°C – 230°C for 6 h. The average size and size distribution of the synthesized particles were below 10 nm and narrow, respectively. The XRD diffraction pattern shows that the synthesized powders were crystalline. This study has shown that the synthesis of Gd2O3 doped CeO2 nanopowders is possible under glycothermal conditions in ethylene glycol solution. The effects of synthesis parameters, such as the solvent ratio of starting solution, pH of starting solution, reaction temperature and time, are discussed.

Characteristics of Thin Films Synthesized from Colloidal Silica-Silane Sols

Three kinds of colloidal silica (CS)/silane sol solutions were synthesized by using three kinds of CS at different reaction time. Sol solutions were prepared from 1034A CS/methyltrimethoxysilane (MTMS), HSA CS/MTMS and LS CS/MTMS materials. In order to understand their physical and chemical properties, sol-gel coating films were fabricated on glass. Coating film on glass, obtained from 1034A/MTMS sol, had high contact angle and much enhanced flat surface in comparison with those of HSA/MTMS and LS/MTMS sols. Enhanced surface properties were observed in the case of sol solutions left for 7 days. With increasing reaction time in sol solutions, surface free energy and roughness in coating films decreased. Good thermal stability was observed in all used films, i.e., no thermal degradation up to 550°C. In the case of 1034A/MTMS coating film, thermal degradation did not occur up to 600°C. In addition, microhardness of 1034/MTMS coating film was higher than those of HSA/MTMS and LS/MTMS due to active networking and surface treatment reactions between 1034A and MTMS.

Properties of Sol-Gel Coating Film from Colloidal Silica-Silane Sol

Two kinds of colloidal silica(CS)/silane sol solutions were prepared. Two sol solutions are involved with the kinds of silane such as methyltrimethoxysilane(MTMS) and -Glycidoxypropyl trimethoxysilane(ETMS) using LS CS. MTMS was added to two sol solutions. Whether ETMS was added or not, two kinds of sol solutions were synthesized. Using two kinds of sol solutions, sol-gel coating films were formed on glass substrates via dip-coating process. Here, seasoning effect of for enhancing properties of sol-gel coating layer on glass was investigated while such sol-gel solutions were left for 7days. Also, their properties such as surface free energy, roughness, thermal property, potential hardness and elastic portion were characterized in order to understand the effect of addition of ETMS. In this case of LS/MTMS sol, the coating film had low surface free energy and more enhanced flat surface than that of the case of LS/MTMS/ETMS sol. ETMS forms hydrophilic hydroxyl group in sol solution, then surface free energy of LS/MTMS/ETMS coating film increased. In the beginning of reaction sol solution seemed to be unstable, but 4days later their coating film properties such as surface free energy and roughness enhanced. The elastic portion of coating films obtained from LS/MTMS/ETMS sol increased with addition of ETMS, but thermal stability decreased.

Effects of Fillers on Electrical Properties of PTFE Composites for Circuit Breaker

This paper presents the effects of fillers on electrical properties of PTFE composites for nozzle of circuit breaker. PTFE has been used widely as a material for circuit breaker nozzle. Adding some filler into PTFE material is expected to be efficient for improving the endurance against arc radiation. In this experiment, effects of fillers on electrical properties such as dielectric constant, dissipation factor, electrical resistivity, dielectric strength and corona resistance of PTFE composites were investigated.

Properties of Coating Films Synthesized from Colloidal Silica and Methyltrimethoxysilane

Colloidal silica/methyltrimethoxysilane (MTMS) sol solutions were prepared in variation with the ratio of MTMS to colloidal silica. Sol solutions were prepared by sol-gel reaction. To understand their physical and chemical properties, dip coating of sol solutions was performed on the glass substrates. The state of coating films was investigated in variation with the amount of MTMS and reaction time. The contact angle and thickness of coating films increased with an increasing amount of MTMS. The surface roughness of coating films decreased with an increasing amount of MTMS. Coating films were stable until 550°C. Thermal degradation temperature of coating films decreased with an increasing amount of MTMS.