• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.30 no.1
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• pp.1-9
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• 2020

Objectives: The purpose of this case study is to assess workers' exposure to carbon nanotubes(CNTs) and characterize particles aerosolized during the process of producing CNT-enabled polytetrafuoroethylene(PTFE) composites at a worksite in Korea. Methods: Personal breathing zone and area samples were collected for determining respirable concentrations of elemental carbon(EC) using NIOSH(National Institute for Occupational Safety and Health) Method 5040. Personal exposure to nano-sized particles was measured as the number concentration and mean diameter using personal ultrafine particle monitors. The number concentration by particle size was measured using optical particle sizers(OPS) and scanning mobility particle sizers(SMPS). Transmission electron microscopy (TEM) area samples were collected on TEM grids and analyzed to characterize the size, morphology, and chemistry of the particles. Results: Respirable EC concentrations ranged from 0.04 to 0.24 ㎍/㎥, which were below 23% of the exposure limit recommended by NIOSH and lower than background concentrations. Number concentrations by particle size measured using OPS and SMPS were not noticeably elevated during CNT-PTFE composite work. Instant increase of number concentrations of nano-sized particles was observed during manual sanding of CNT-PTFE composites. Both number concentrations and mean diameters did not show a statistically significant difference between workers handing CNT-added and not-added materials. TEM analyses revealed the emission of free-standing CNTs and CNT-PTFE aggregate particles from the powder supply task and composite particles embedded with CNTs from the computer numerical control(CNC) machining task with more than tens of micrometers in diameter. No free-standing CNT particles were observed from the CNC machining task. Conclusions: Significant worker exposure to respirable CNTs was not found, but the aerosolization of CNTs and CNT-embedded composite particles were observed during handing of CNT-PTFE powders and CNC machining of CNT-PTFE composites. Considering the limited knowledge on the toxicity of CNTs and CNT composite particles to date, it seems prudent to take a precautionary approach for the protection of workers' health.

• Membrane Journal
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• v.25 no.1
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• pp.48-59
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• 2015

This paper reports a fabrication of poly(L-lactic acid) (PLLA) scaffold membranes through phase separation process using pure and mixed solvents. Chloroform and 1,4-dioxane were used as pure solvents and mixed solvents were obtained by mixing the pure solvents together. Morphologies, mechanical properties and mass transfer characteristics of the scaffold membranes were investigated through SEM, stress-strain test and glucose diffusion test. Scaffold membranes from the solution with pure chloroform showed solid-wall pore structure. In contrast, nano-fibrous membranes were fabricated from the solution with pure 1,4-dioxane. In case of mixed solvents, the scaffold membranes showed various structures with changing composition of the solvents. When 1,4-dioxane content was lower than 20 wt% in the solvent, scaffold membrane showed solid-wall pore structure. When the content was 20 wt%, scaffold membranes with macropores with the maximum size of $100{\mu}m$ was obtained. In the concentration range of 1,4-dioxane over 25 wt%, the scaffold membranes showed nano-fibrous structures. In this range, the fibers showed different diameters with changing composition of the solvent. The minimum fiber diameter was about $15{\mu}m$, when 1,4-dioxane composition was 80 wt%. These results indicate that the composition of the solvent showed a significant effect on the structure of scaffold membrane.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.2
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• pp.57-62
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• 2011

The energy conversion efficiency of DSSCs (Dye-Sensitized Solar Cells) is dependent on the powder size, the structure, and the morphology of $TiO_2$ electrode. The higher efficiency is obtained with high surface area of the nanoanatase-$TiO_2$ powder adsorbed onto a lot more of the dye. Also, the enhancement of light scattering increases the efficiency with high adsorption of the dye. Powder size, crystalline phase, and shape of $TiO_2$ obtained by hydrothermal method have 15-20 nm, anatase and round. $TiO_2$ electrode has fabricated with the mixture of scattering $TiO_2$ particle with 0.4 ${\mu}m$ in nano-sized powder. Conversion efficiency of series of DSSCs was measured with volume fraction of scattering particle. Photovoltaic characteristics of DSSCs with 10% scattering particles are 3.51 mA for Jsc (short circuit current), 0.79 V for Voc(open circuit potential), filling factor 0.619 and 6.86% for efficiency. Jsc was improved by 11% and enhancement of efficiency by 0.77% compared with that of no scattering particles. The confinement of inserted light by light scattering particles has more increase of the injection of exiton(electron-hole pair) and decrease of moving path in electron. Efficiencies of DSSCs with more than 10% for scattering particles have reduced with increasing the pore in the $TiO_2$ electrode.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.418-423
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• 2009

MWCNT(multi-wall carbon nanotube)-doped PEDOT:PSS(poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), used as a HIL(hole injection layer) material in OLEDs(organic light emitting diodes), was spin-coated on to the ITO glass to form PEDOT:PSS-MWCNT nano composite thin film. Morphology and transparency characteristics of nano composite thin films with respect to the loading percent of MWCNT have been investigated using FT-IR, UV-Vis and SEM. Furthermore, ITO/PEDOT:PSS-MWCNT/NPD/$Alq_3$/Al devices were fabricated, and then J-V and L-V characteristics were investigated. Functional group-incorporated MWCNT was prepared by acid treatment and showed good dispersion property in PEDOT:PSS solution. PEDOT:PSS-MWCNT thin films possessed good transparency property. For multi-layered devices, it was shown that as the loading percent of MWCNT increased, the current density increased but the luminance dramatically decreased. It might be conclusively suggested that the enhanced charge mobility by MWCNT could increase the current density but the hole trapping property of MWCNT could dramatically decrease the hole mobility in the current devices.

• Journal of Korean Neurosurgical Society
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• v.63 no.6
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• pp.698-706
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• 2020

Objective : To study the physiochemical characteristics of podophyllotoxin (PPT) conjugated stearic acid grafted chitosan oligosaccharide micelle (PPT-CSO-SA), and evaluate the ability of the potential antineoplastic effects against glioma cells. Methods : PPT-CSO-SA was prepared by a dialysis method. The quality of PPT-CSO-SA including micellar size, zeta potential, drug encapsulation efficiency and drug release profiles was evaluated. Glioma cells were cultured and treated with PPT and PPT-CSO-SA. The ability of glioma cells to uptake PPT-CSO-SA was observed. The proliferation of glioma cells was determined by 3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay. The apoptosis and morphology of U251 cells were observed by 4',6-Diamidino-2-phenylindole dihydrochloride (DAPI) dye staining. Cell cycle analysis was performed by flow cytometry. The migration ability of U251 cells was determined by wound healing test. Results : PPT-CSO-SA had nano-level particle size and sustained release property. The encapsulation efficiency of drug reached a high level. The cellular uptake percentage of PPT in glioma cells was lower than that of PPT-CSO-SA (p<0.05). The inhibitory effect of PPT-CSO-SA on glioma cells proliferation was significantly stronger than that of PPT (p<0.05). The morphologic change of apoptosis cell such as shrinkage, karyorrhexis and karyopyknosis were observed. The percentage of U251 cells in G2/M phase increased significantly in the PPT-CSO-SA group compared with PPT group (p<0.05). Compared with the PPT group, the cell migration ability of the PPT-CSO-SA group was significantly inhibited after 12 and 24 hours (p<0.05). Conclusion : PPT-CSO-SA can effectively enhance the glioma cellular uptake of drugs, inhibit glioma cells proliferation and migration, induce G2/M phase arrest of them, and promote their apoptosis. It may be a promising anti-glioma nano-drug.

• Journal of the Korean Vacuum Society
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• v.18 no.5
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• pp.358-364
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• 2009

We investigated the growth of ZnO thin films with prominent emission characteristics through minimizing the formation of defects by using pulsed laser deposition (PLD). To do so, the ZnO films were deposited on sapphire(0001) substrates at the substrate temperature of $400-850^{\circ}C$ and then the variation of their structural and optical properties were analyzed by x-ray diffraction, atomic force microscope and photoluminescence. As a result, all ZnO films were grown with c-axis preferential orientation irrespective of the substrate temperature. However, the crystallinity and stress state were dependent on the substrate temperature and the ZnO film deposited at $600^{\circ}C$ showed the best surface morphology and crystallinity with nearly no strain. And also this film exhibited outstanding emission characteristics from the viewpoint of full width half maximum of UV emission peak as well as visible emission due to defects. These results indicate that the emission characteristics of the ZnO films are strongly related to their structural characteristics influenced by substrate temperature. Consequently, ZnO films with strong UV emission and nearly no visible emission, which are applicable to UV emission devices, could be grown at the substrate temperature of $600^{\circ}C$ by PLD.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.30 no.2
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• pp.153-162
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• 2020

Objectives: 3D printing technologies have become widely developed and are increasingly being used for a variety of purposes. Recently, the evaluation of 3D printing operations has been conducted through chamber test studies, and actual workplace studies have yet to be completed. Therefore, the objective of this study was to determine the emission of volatile organic compounds(VOCs), metals, and particles from printing operations at a workplace. This included monitoring conducted at a commercial 3D printing service workplace where the processes involved material extrusion, material jetting, binder jetting, vat photo polymerization, and powder bed fusion. Methods: Area samples were collected with using a Tenax TA tube for VOC emission and MCE filter for metals in the workplace. For particle monitoring, Mini Particle Samplers(MPS) were also placed in the printer, indoor work area, and outdoor area. The objective was to analyze and identify particles' size, morphology, and chemical composition using transmission electron microscopy with energy dispersive spectroscopy(TEM-EDS) in the workplace. Results: The monitoring revealed that the concentration of VOCs and metals generated during the 3D printing process was low. However, it also revealed that within the 3D printing area, the highest concentration of total volatile organic compounds(TVOC) was 4,164 ppb at the vat photopolymerization 3D printing workplace, and the lowest was 148 ppb at the material extrusion 3D printing workplace. For the metals monitoring, chromium, which, is carcinogenic for humans, was detected in the workplace. As a characteristic of the particles, nano-sized particles were also found during the monitoring, but most of them were agglomerated with large and small particles. Conclusions: Based on the monitoring conducted at the commercial 3D printing operation, the results revealed that the concentration of VOCs and metals in the workplace were within Korea's occupational exposure limits. However, due to the emission of nano-sized particles during 3D printing operations, it was recommended that the exposure to VOCs and metals in the workplace should be minimized out of concern for workers' health. It was also shown that the characteristics of particles emitted from 3D printing operations may spread widely within an indoor workplace.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.447-451
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• 2007

We investigated the dependence of the various annealing conditions and thickness ($6\sim45nm$) of the Ti-doped $Al_2O_3$ coating on the electrochemical properties and the capacity fading of Ti-doped $Al_2O_3$ coated $LiCoO_2$ films. The Ti-doped-$Al_2O_3$-coating layer and the cathode films were deposited on $Al_2O_3$ plate substrates by RF-magnetron sputter. Microstructural and electrochemical properties of Ti-doped-$Al_2O_3$-coated $LiCoO_2$ films were investigated by transmission electron microscopy (TEM) and a dc four-point probe method, respectively. The cycling performance of Ti-doped $Al_2O_3$ coated $LiCoO_2$ film was improved at higher cut-off voltage. But it has different electrochemical properties with various annealing conditions. They were related on the microstructure, surface morphology and the interface condition. Suppression of Li-ion migration is dominant at the coating thickness >24.nm during charge/discharge processes. It is due to the electrochemically passive nature of the Ti-doped $Al_2O_3$ films. The sample be made up of Ti-doped $Al_2O_3$ coated on annealed $LiCoO_2$ film with additional annealing at $400^{\circ}C$ had good adhesion between coating layer and cathode films. This sample showed the best capacity retention of $\sim92%$ with a charge cut off of 4.5 V after 50 cycles. The Ti-doped $Al_2O_3$ film was an amorphous phase and it has a higher electrical conductivity than that of the $Al_2O_3$ film. Therefore, the Ti-doped $Al_2O_3$ coated improved the cycle performance and the capacity retention at high voltage (4.5 V) of $LiCoO_2$ films.

• Korean Journal of Microbiology
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• v.46 no.3
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• pp.262-269
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• 2010

To investigate a quantitative evaluation of the actinobacteria, we have collected samples from various kinds of bamboo forest soil. Each different layers contained $2.7{\times}10^6-2.7{\times}10^8$ CFU/g of actinobacteria which was the highest in litter layers of Sasa boreali forest soil. We obtained 330 actinobacteria from different layers of bamboo forest soil; litter (100 strains), humus (70 strains), and rhizosphere soil (160 strains). Based on the colony morphology (aerial mycelium, substrate mycelium, and soluble pigment), isolates were divided into thirty-six groups and we selected 50 representative isolates. 16S rRNA gene sequence analysis showed Streptomyces was major actinobacteria (94%) and they were categorized as cluster I (2 strains), II (35 strains), III (6 strains), and IV (7 strains), respectively. The diversity index of 50 Streptomyces collected from the bamboo forest soil was calculated with the Shannon-Wiener method. Bamboo litter showed higher diversity index level of 3.33 than that of humus and rhizosphere soil. Also, antibiotic activities of our isolates were investigated against Botrytis cinerea, Xanthomonas campestris, Xanthomonas axonopodis pv. vesicatoria, and Bacillus cereus and found in 74, 16, 25, and 24 strains, respectively.

• Korean Chemical Engineering Research
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• v.43 no.2
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• pp.313-317
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• 2005

Synthetic gene carriers such as poly-cationic polymers easily form complexes with plasmid DNA which contains negative charge. Chitosan is a polysaccharide that demonstrates much potential as a gene delivery system. The ability of depolymerized chitosan to condense DNA was determined using electrophoresis. Dynamic laser scattering and scanning electron microscopy were used to examine the size and the morphology of the chitosan/DNA complex. Parameters such as chitosan molecular weight and charge density influenced the complex size and the DNA amount condensed with chitosan. The cell viabilities in the presence of chitosan ranged between 84-108% of the control in all experiments. Gene expression efficacy using chitosan/DNA complex was enhanced in 293 cells relative to that using naked DNA, although it was lower than that using lipofecamine. Transfection efficacy using low molecular weight chitosan (Mw=8,517) was higher than those of the control and the other chitosan (MW=4,078). The low molecular weight chitosan (MW=8,517) with a high charge density (18.32 mV) fulfilled the requirements for a suitable model gene delivery system with respect to the condensing ability of DNA, complex formation, and transfection efficacy.