• The Korean Journal of Rheology
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• v.3 no.1
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• pp.76-85
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• 1991

적은양의 분자량이 큰선형 고부자를 수용액에 첨가함으로서 얻어지는 마찰저항가소 연구가 rotating disk 장치를 이용해 수행되었다. 마찰저항 감소제로 poly(ethylene oxide)와 poly(acrylamide)를 사용하였으며 고분자 분자량 고분자 농도, disk 의 회전속도 및 온도 등 여러 가지 인자에 대한 마찰정항감소의 의존성을 연구하였다. 또한 마찰저항 감소 효과와 고분자 용액의 점도평균 분자량을 동시에 측정함으로서 고분자 퇴화에 대한 연구도 수행하 였다. 마찰저항감소는 고분자 농도가 증가함에 따라 임계농도에 도달할때까지 증가하였고 낮은 농도에서는 분자량이 큰 고분자일수록 더욱 큰 마찰저항 감소효과를 나타내었다. 마찰 감소 진행 중의 높은 전단력에 기인하는 고분자의 분해는 고분자 농도가 낮은데에서 더욱두 드러지게 나타났으며 온도 효과의 연구로부터 poly(acrylamide)가 poly(ethylene oxide)보다 열적으로 안정함을 알수 있었다.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3603-3609
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• 2011

A novel sampling method of the headspace poly(dimethylsiloxane) (PDMS) mini-disk extraction (HS-PDE) was developed, optimized, validated and applied for the GC/MS analysis of spices flavors. A prototype PDMS mini-disk (8 mm outer diameter, 0.157 mm thickness, 9.4 mg weight) has been designed and fabricated as a sorption device. The technique uses a small PDMS mini-disk and very small volume of organic solvent and less sample size than the solvent extraction. This new HS-PDE method is very simple to use, inexpensive, rapid, requires less labor. Linearities of calibration curves for ${\alpha}$-pinene, ${\beta}$-pinene, limonene and ${\gamma}$-terpinene by HS-PDE combined with GC/MS were excellent having $r^2$ values greater than 0.99 at the dynamic range of 6.06~3500 ng/mL. The limit of detection (LOD) and the limit of quantitation (LOQ) showed very low values. This method exhibited good precision and accuracy. The overall extraction efficiency of this method was evaluated by using partition coefficients ($K_p$) and concentration factors (CF) for several characteristic components from nutmeg and mace. Partition coefficients were in the range from $2.04{\times}10^4$ to $4.42{\times}10^5$, while CF values were 0.88-15.03. HS-PDE was applied successfully for the analysis of flavors compositions from nutmeg, mace and cumin. The HS-PDE method is a very promising sampling technique for the characterization of volatile flavors.

• Tribology and Lubricants
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• v.20 no.4
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• pp.197-203
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• 2004

As the rotational speed and the track density are increased, the vibration of disk/spindle system becomes critical issue in order to reduce the track mis-registration. In this work, we propose a simple inclined air bearing (20${\times}$20 mm) system which is located very near to the rotating poly-carbonate disk, and investigate suppressing effect for the disk vibration mode (0,0) both experimentally and numerically. We find dynamic stiffness and damping coefficients of air bearing and then apply those values to the disk vibration analysis. Numerical results show about 10 percent difference comparing to the experimental results. Also we investigate the reduction of disk vibration and power consumption with two different kinds of inclined bearing for the normal disk drive system experimentally. We find inclined air bearing can reduce about 30 percents of the transverse disk vibration.

• Bulletin of the Korean Chemical Society
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• v.27 no.11
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• pp.1763-1768
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• 2006

The application of poly(Co(II)-(1,8-diaminonaphthalene))(poly(Co-DAN)) and poly(1,8-diaminonaphthalene) (Poly(1,8-DAN)) to the electrocatalytic reduction of molecular oxygen was investigated, which were electrochemically grown by the potential cycling method on the glassy carbon electrodes. The reduction of oxygen at the polymer and its metal complex polymer coated electrodes were irreversible and diffusion controlled. The Poly(1,8-DAN) and Poly(Co-DAN) films revealed the potential shifts for the oxygen reduction to 30 mV and 110 mV, respectively, in an aqueous solution, compared with that of the bare electrode. Hydrodynamic voltammetry with a rotating ring-disk electrode showed that Poly(1,8-DAN) and Poly(Co-DAN) coated electrodes converted respectively 84% and 22% of $O_2$ to $H_2O$ via a four electron reduction pathway.

• Bulletin of the Korean Chemical Society
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• v.23 no.3
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• pp.399-403
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• 2002

The complex of iron(II) tris(3-Br-phen) (3-Br-phen; 3-bromo-1,10-phenanthroline) was prepared as a precursor of electropolymerization and the crystal structure of [Fe(3-Br-phen)3]($PF_6$)2${\cdot}$CH3CN with a distorted octahedral geometry has been investigated. The reductive electropolymerization of $>[Fe(3-Br-phen)3]^{2+}$ complex onto the surface of a glassy carbon electrode and indium tin oxide (ITO) optically transparent electrode were performed in acetonitrile at room temperature. Thin film of poly-$>[Fe(3-Br-phen)3]^{2+}$ formed was adherent, electroactive and stably deposited on a glassy carbon disk electrode. The thin metallopolymeric film formed was also confirmed by absorption spectroscopy.

• Polymer(Korea)
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• v.34 no.5
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• pp.474-479
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• 2010

We developed laminated cylindrical scaffolds composed of poly(lactide-co-glycolide)(PLGA) and keratin, and investigated their potential for tissue engineering and disk regeneration. The scaffold was designed to have two parts, i.e. inner cylinder and outer disk, to mimic a natural disk. The outer disk was composed of PLGA and the inner cylinder was prepared using PLGA film or PLGA/keratin hybrid film. In this study, we investigated the effects of keratin on the growth and proliferation of annulus fibrous(AF) cells in the cylindrical scaffolds. Scaffolds containing PLGA/keratin films showed a significantly higher cell proliferation and expression of collagen I and II than the counterpart with PLGA films. Keratin containing scaffolds also exhibited an excellent mechanical strength, demonstrating that keratin influences the proliferation of annulus fibrous cells. The results provide valuable information on PLGA/keratin films for tissue engineered disk regeneration.

• Journal of Electrochemical Science and Technology
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• v.14 no.1
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• pp.21-30
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• 2023

This work presents a correlation between the behavior of formic acid oxidation (FAO) on various Bi-modified Pt(poly) disk electrodes and their morphologies observed on Bi-modified Pt(111) disk electrodes using electrochemical scanning tunneling microscopy (EC-STM) to understand the effects of Bi on Pt. To distinguish the FAO activities of Bi on Pt and plain Pt around Bi, additional Pt was intentionally deposited using two different routes: direct route and iodine route. In direct route, Pt was directly deposited on Bi islands and plain Pt sites around Bi islands, while in iodine route, Pt was exclusively deposited on Bi islands by protecting plain Pt sites with adsorbed iodine. Thus, a comparison of FAO performances on the two Bi-modified Pt electrodes with additional Pt (deposited in the different ways) disclosed a difference in FAO performances on plain Pt sites and Bi islands. When Bi coverage was ~0.04, the Bi deposits were scattered Bi islands enhancing FAO on Pt(poly). The additional Pt deposits using direct route increased FAO efficiency, while the ones using iodine route slightly decreased FAO current. The EC-STM observations indicated that Pt deposits around Bi islands, not on Bi islands, were responsible for the FAO current increase on Bi-modified Pt(poly). The FAO efficiency on Bi-modified Pt(poly) with a Bi coverage of ~0.25 increased by a factor of 2. However, the additional Pt deposits using the two Pt deposition routes notably decreased the FAO current. The dependency of FAO on Bi coverage was discussed in terms of electronic effect and ensemble effect.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.152-155
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• 2004

Effects of sliding speed, applied load, counterpart radius and thickness of PMMA (Poly Methyl Methacrylate) coating layers on their dry sliding frictional and wear behavior were investigated. Sliding wear tests were carried out using a pin-on-disk wear tester. The PMMA layer was coated on Si wafer by a sol-gel technique with two different thicknesses, $1.5{\mu}m\;and\;0.8{\mu}m$. AISI 52100 bearing steel balls were used as a counterpart of the PMMA coating during the wear. Normal applied load and sliding speed were varied. Wear mechanisms were investigated by examining worn surfaces by an SEM. Under most of sliding test conditions, the thicker layer with the thickness of $1.5{\mu}m$ showed lower fiction coefficient than the thinner layer. Effects of sliding speed and counterpart's radius on the frictional behavior were varied depending on the thickness of the coating layer.

• Korea-Australia Rheology Journal
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• v.16 no.2
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• pp.57-62
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• 2004

Turbulent drag reduction (DR) efficiency of water soluble poly(ethylene oxide) (PEO) with two different molecular weights was studied as a function of polymer concentration and temperature in a turbulent flow produced via a rotating disk system. Its mechanical degradation behavior as a function of time in a turbulent flow was also analyzed using both a simple exponential decay function and a fractional exponential decay equation. The fractional exponential decay equation was found to fit the experimental data better than the simple exponential decay function. Its thermal degradation further exhibited that the susceptibility of PEO to degradation increases dramatically with increasing temperature.

• Bulletin of the Korean Chemical Society
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• v.28 no.8
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• pp.1322-1328
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• 2007

The catalytic activity of poly[(2,2'-bipyridine)copper(II)-μ4-oxalato] coated on a glassy carbon electrode (GCE) for O2 electroreduction is examined using cyclic voltammetry and rotating disk electrode techniques. The cyclic voltammograms show that O2 is electroreduced on pBpCuOx-coated GCE surfaces at a peak potential of ? 0.25 V in pH 4.7 acetate buffer media. The electroreduction of O2 on pBpCuOx-coated GCE occurs at 450 mV more positive potential than that found at a bare GCE. The catalytic activity originates from Cu(II) coordinated by bipyridine in the complexes and the polymer type Cu-complex films exhibit an enhanced stability compared to monomeric Cu-complexes during the O2 electroreduction. The rotating disk electrode measurements reveal that the electroreduction of O2 on pBpCuOx-coated GCE is a four-electron process. Kinetic parameters for O2 reduction on pBpCuOx-coated GCE are obtained from rotating disk experiments and compared with those on bare glassy carbon electrode surfaces.