• Polymer(Korea)
• /
• v.27 no.6
• /
• pp.542-548
• /
• 2003

Nanoparticles with unsaturated poly(hydroxyalkanoate)s (UPHAs) biosynthesized with Pseudo-monas oleovorans were prepared by spontaneous emulsification solvent diffusion method. The influence of nanoparticle formation was investigated with various experimental parameters such as sonication conditions, sol-vent, surfactant and polymer contents, etc. The physical and chemical properties of UPHAS and its nanoparticles were characterized using $^1$H- and $\^$13/C-nuclear magnetic resonance spectroscopies, attenuated total reflection infrared spectroscopy, differential scanning calorimetry and gel permeation chromatography. The morphology of particles was observed using scanning electron microscope and the size and distribution of nanoparticles were measured with electrophoretic light scattering spectrophotometer. The mean diameter of particles decreased with increasing sonication amplitude and time. The addition of ethanol into UPHAS chloroform solution decreased the particle size presumably due to increased solvent diffusion into water phase. The particle size increased with increased the concentration of UPHAS solution. Under the 2-4％ poly(vinyl alcohol) (PVA) aqueous solution the minimum mean diameter of particles was shown. The higher degree of hydrolysis and degree of polymerization of PVA increased the mean diameter of particles.

• Macromolecular Research
• /
• v.16 no.1
• /
• pp.6-14
• /
• 2008

Polypropylene (PP)-layered silicate nanocomposites were developed using a new processing method involving a supercritical carbon dioxide ($scCO_2$)-assisted co-rotating twin-screw extrusion process. The nanocomposites were prepared through two step extrusion processes. In the first step, the PP/clay mixture was extruded with $CO_2$ injected into the barrel of the extruder and the resulting foamed extrudate was cooled and pelletized. In the second step, the foamed extrudate was extruded with venting to produce the final PP/clay nanocomposites without $CO_2$. In this study, organophilic-clay and polypropylene matrix were used. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer. This study focused on the effect of $scCO_2$ on the dispersion characteristics of the clays into a PP matrix and the rheological properties of the layered silicate based PP nanocomposites. The dispersion properties of clays in the nanocomposites as well as the rheological properties of the nanocomposites were examined as a function of the PP-g-MA concentration. The degree of dispersion of the clays in the nanocomposites was analyzed by X-ray diffraction and transmission electron microscope. Various rheological properties of the nanocomposites were measured using a rotational rheometer. In the experimental results, the $scCO_2$ assisted continuous manufacturing extrusion system was used to successfully produce the organophilic-clay filled PP nanocomposites. It was found that $scCO_2$ had a measurable effect on the clay dispersion in the polymer matrix and the melt intercalation of a polymer into clay layers.

• Journal of the Korean Magnetics Society
• /
• v.16 no.1
• /
• pp.66-70
• /
• 2006

Magnetite nanoparticles, which have been extensively used in many fields, were encapsulated with a natural polymer, chitosan, to improve their biocompatibility. We have synthesized magnetite $(Fe_3C_4)$ nanoparticles using chemical coprecipitation technique with sodium oleate as surfactant. Nanoparticle size can be varied from 1.2 to 7.4nm by controlling the sodium oleate concentration. Magnetite phase nanoparticles could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with sodium oleate and chitosan have been prepared. High magnetic property chitosan-microsphere particles were prepared from oleate-coated magnetite suspension using spray method. The surftce, and tile morphology of the magnetic chitosan microsphere particles were characterized using optical microscope and scanning electron microscope. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the chitosan microspheres including magnetite nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles.

• Journal of the Korean Wood Science and Technology
• /
• v.27 no.3
• /
• pp.63-72
• /
• 1999

For the purpose of improving the wet strength properties of paper, cellulosic fibers were modified by the processes of carbarmoylethylation and N-chlorocarbamoylethylation. Carbamoylethylated cellulose was prepared by the reaction of acrylamide with cellulosic fibers under the alkali catalyst, and N-chlorocarbamoylethylated cellulose was prepared by the addition of sodium hypochlorite into the carbamoylethylated cellulose. In carbamoylethylation reaction, the conditions of NaOH concentration, temperature and acrylamide addition rate were considered to be important factors. An initial reactivity and degree of substitution(DS) in carbamoylethylation of cellulosic fibers were effective according to increasing the addition rates of alkali, acrylamide and the temperature condition of $40^{\circ}C$. The effective wet strength properties by N-chlorocarbamoylethylation of cellulosic fibers were indicated under the conditions of DS 0.06. The wet strength of sheet was improved to 85% at the 100% basis of dry strength. From the photograph of scanning electron microscopy, fiber cuttings on the edge of sheet sample used in tensile strength testing were found in the N-chlorocarbamoylethylated sheet, due to the improvement of fiber bonding strength. The hypochlorite treatment was effective in the recycling of N-chlorocarbamoylethylated sheet, and was reduced the wet strength of sheet to be able to reslush.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.636-636
• /
• 2013

Since first discovery of strong Raman spectrum of molecules adsorbed on rough noble metal, surface enhanced Raman scattering (SERS) has been widely used for detection of molecules with low concentration. Surface plasmons at noble metal can enhance Raman spectrum and using Au nanostructures as substrates of SERS has advantages due to it has chemical stability and biocompatibility. However, the photoluminescence (PL) background from Au remains a problem because of obtaining molecular vibration information. Recently, graphene, two-dimensional atomic layer of carbon atoms, is also well known as PL quenchers for electronic and vibrational excitation. In this study, we observed SERS of single layer graphene on or under monolayer of Au nanoparticles (NPs). Single layer graphene is grown by chemical vapor deposition and transferred onto or under the monolayer of Au NPs by using PMMA transfer method. Monolayer of Au NPs prepared using Langmuir-Blodgett method on or under graphene surface provides closed and well-packed monolayer of Au NPs. Scanning electron microscopy (SEM) and Raman spectroscopy (WItec, 532 nm) were performed in order to confirm effects of Au NPs on enhanced Raman spectrum. Highly enhanced Raman signal of graphene by Au NPs were observed due to many hot-spots at gap of closed well-packed Au NPs. The results showed that single layer graphene provides larger SERS effects compared to multilayer graphene and the enhancement of the G band was larger than that of 2D band. Moreover, we confirm the appearance of D band in this study that is not clear in normal Raman spectrum. In our study, D band appearance is ascribed to the SERS effect resulted from defects induced graphene on Au NPs. Monolayer film of Au NPs under the graphene provided more highly enhanced graphene Raman signal compared to that on the graphene. The Au NPs-graphene SERS substrate can be possibly applied to biochemical sensing applications requiring highly sensitive and selective assays.

• Journal of Microbiology and Biotechnology
• /
• v.23 no.7
• /
• pp.942-952
• /
• 2013

Monoliths are functional porous materials with a three-dimensional continuous interconnected pore structure in a single piece. A monolith with uniform shape based on poly(${\gamma}$-glutamic acid) (PGA) has been prepared via a thermally induced phase separation technique using a mixture of dimethyl sulfoxide, water, and ethanol as solvent. The morphology of the obtained monolith was observed by scanning electron microscopy and the surface area of the monolith was evaluated by the Brunauer Emmett Teller method. The effects of fabrication parameters such as the concentration and molecular mass of PGA and the solvent composition have been systematically investigated. The PGA monolith was cross-linked with hexamethylene diisocyanate to produce the water-insoluble monolith. The addition of sodium chloride to the phase separation solvent affected the properties of the cross-linked monolith. The swelling ratio of the cross-linked monolith toward aqueous solutions depended on the buffer pH as well as the monolith fabrication condition. Copper(II) ion was efficiently adsorbed on the cross-linked PGA monolith, and the obtained copper-immobilized monolith showed strong antibacterial activity for Escherichia coli. By combination of the characteristic properties of PGA (e.g., high biocompatibility and biodegradability) and the unique features of monoliths (e.g., through-pore structure, large surface area, and high porosity with small pore size), the PGA monolith possesses large potentials for various industrial applications in the biomedical, environmental, analytical, and separation fields.

• Environmental Analysis Health and Toxicology
• /
• v.13 no.3_4
• /
• pp.105-115
• /
• 1998

Reactive oxygen species (ROS) are highly reactive molecules due to their unpaired electron. They have been suspected as one of the major tissue damage inducers in biological metabolic systems. Antioxidant enzymes, such as catalase and superoxide dismutase, could not repair all the oxidative damages resulting from those excessive toxic ROS. It is, therefore, urgent to develop effective antioxidants to relieve from the oxidatire damages. In this study antioxidative effects were investigated by using two flavonoids such as quercetin and naringenin and a flavonoid-rich extract, Ginkgo biloba extract in combination with paraquat that is known as a strong generator of oxygen radicals. The results are summeringed as follows: 1. To assess radical scavenging ability reduction concentrations (IC$_{50}$) of 1,1-diphenyl-2-picrylhydrazine (DPPH) within 15 minutes were measured. The values of the IC$_{50}$ of quercetin and Ginkgo biloba extract were 15.4 $\mu$M and 13.2$\mu$g/ml, respectively. Their radical removing activities showed concentration-dependent manners. 2. In the hydrogen peroxide assay by using PMS-NADH system, quercetin, naringenin and Ginkgo biloba extract led to removing hydrogen peroxide in concentrationdependent manner whose removing abilities at 100$\mu$M or 100 $\mu$g/ml were 75.6, 25.8 and 26.0%, respectively. 3. In the hydrogen peroxide-induced rat blood hemolysis assay all three compounds led to similar effects whose hemolysis inhibition ratios at 100$\mu$M or 100$\mu$g/ml were 68.0, 5.14 and 55.8%, respectively. 4. In the xanthinee oxidase assay by measuring degree of NADH oxidation in the presence of hypoxanthine and xanthinee oxidase, both quercetin and Ginkgo biloba extract showed excellent activities showing 42.8 and 24.2% inhibiting xanthine oxidase activity at 100$\mu$M or 100$\mu$g/ml concentrations, respectively.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.32 no.2
• /
• pp.139-143
• /
• 1999

The antimicrobial action of bacteriocin produced by lactobacillus sp. GM7311 against three Gram negative bacteria, Proteus mirabilis, Vibrio parahaemolyticus, and Escherichia coli, was investigated, When the bacteriocin was added to the culture at different stages, viable cells of all of the indicator strains tested were decreased, even though the most inhibited indicator cell growth stages were different. Transmission electron microscopic observation of indicator strains treated with bacteriocin revealed cell Iysis, indicating the cell membrane appears to be the primary site of action. The amino acids concentration of indicator strains treated with bacteriocin were diminished and fatty acids compositions were changed as compared with controls.

• Archives of Pharmacal Research
• /
• v.26 no.1
• /
• pp.76-82
• /
• 2003

Drug releasing porous poly($\varepsilon$-caprolactone) (PCL)-chitosan matrices were fabricated for bone regenerative therapy. Porous matrices made of biodegradable polymers have been playing a crucial role as bone substitutes and as tissue-engineered scaffolds in bone regenerative therapy. The matrices provided mechanical support for the developing tissue and enhanced tissue formation by releasing active agent in controlled manner. Chitosan was employed to enhance hydrophilicity and biocompatibility of the PCL matrices. PDGF-BB was incorporated into PCL-chitosan matrices to induce enhanced bone regeneration efficacy. PCL-chitosan matrices retained a porous structure with a 100-200 $\mu$m pore diameter that was suitable for cellular migration and osteoid ingrowth. $NaHCO_3$ as a porogen was incorporated 5% ratio to polymer weight to form highly porous scaffolds. PDGF-BB was released from PCL-chitosan matrices maintaining therapeutic concentration for 4 week. High osteoblasts attachment level and proliferation was observed from PCL-chitosan matrices. Scanning electron microscopic examination indicated that cultured osteoblasts showed round form and spread pseudopods after 1 day and showed broad cytoplasmic extension after 14 days. PCL-chitosan matrices promoted bone regeneration and PDGF-BB loaded matrices obtained enhanced bone formation in rat calvarial defect. These results suggested that the PDGF-BB releasing PCL-chitosan porous matrices may be potentially used as tissue engineering scaffolds or bone substitutes with high bone regenerative efficacy.

• Elastomers and Composites
• /
• v.38 no.2
• /
• pp.139-146
• /
• 2003

In this work, the influence of ozone treatment on surface properties of carbon black is investigated in terms of X-ray photoelectron spectroscopy (XPS) and contact angles. And their mechanical interfacial properties of the carbon black/acrylonitrile butadiene rubber (NBR) compounds are studied by the crosslink density and composite tearing energy ($G_{IIIC}$). As a result, it is found that the increasing of the ozone concentration leads to an increase of the introduction rate of oxygen-containing functional groups onto carbon black surfaces and to an increase of the surface free energy, resulting in improving both crosslink density and tearing energy ($G_{IIIC}$) of the compounds. The results can be explained by the fact that the oxygen-containing functional groups of carbon black surfaces make an increase of the degree of adhesion at interfaces between carbon blacks and rubber matrix.