• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.113-116
• /
• 2003

To maximize the productivity in machining molds and dies, machine tools should operate at high speeds. During the high speed operation of moving frames or spindles, vibration problems are apt to occur if the machine tool structures are made of conventional steel materials with inferior damping characteristics. However, self-excited vibration or chatter is bound to occur during high speed machining when cutting speed exceeds the stability limit of machine tool. Chatter is undesirable because of its adverse effect on surface finish, machining accuracy, and tool lift. Furthermore, chatter is a major cause of reducing production rate because, if no remedy can be found, metal removal rates have to be lowered until vibration-free performances is obtained. Also, the resonant vibration of machine tools frequently occurs when operating frequency approaches one of their natural frequencies because machine tools have several natural frequencies due to their many continuous structural elements. However, these vibration problems are closely related to damping characteristics of machine tool structures. This paper presents the use of polymer concrete and sandwich structures to overcome vibration problems. The polymer concrete has high potential for machine tool bed due to its good damping characteristics with moderate stiffness. In this study, a polymer concrete bed combined with welded steel structure i.e., a hybrid structure was designed and manufactured for a high-speed gantry-type milling. Also. its dynamic characteristics were measured by modal tests.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.32-36
• /
• 2002

High-speed movement and high-precision machining are the two most important requirements of present machine tool structures to reduce machining time and to increase the precision of products in various industrial fields such as semiconductor, automobile, and mold fabrication. The high speed operation of machine tools tue usually restricted not only by the low stiffness but also by the low damping of machine tool structures, which induces vibration during high speed machining. If the damping of machine tool structures is low, self induced or regenerative vibrations are bound to occur at high speed operation because the natural frequencies of machine tool structures can not be increased indefinitely. Therefore, the high damping capacity of a machine tool structure is an important factor for high speed machine tool structures. Polymer concrete has high potential for machine tool bed due to its good damping characteristics. In this study, a polymer concrete bed combined with welded steel structure i.e., a hybrid structure was desisted and manufactured for a high-speed gantry-type milling machine through static and dynamic analyses using finite element method. Then the dynamic characteristics were tested experimentally.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.2
• /
• pp.405-408
• /
• 2009

In this work multiwalled carbon nanotube (MWCNT)/fibrin hybrid structures were synthesized via the transglutaminase- catalyzed polymerization of fibrinogen (FBG). Specifically, FBG was tethered onto oxidized MWCNTs by amide coupling, and the in situ polymerization of FBG to fibrin was performed by plasma transglutaminase (Factor XIIIa) in the presence of thrombin. The attached FBG was found to be biologically active and was polymerized to fibrin by thrombin and Factor XIIIa. MWCNT-FBG and MWCNT-Fibrin structures were characterized by FT-IR spectroscopy, transmission electron microscopy, and energy-dispersive X-ray (EDX) spectroscopy.

• Polymer(Korea)
• /
• v.37 no.1
• /
• pp.41-46
• /
• 2013

The glass transition temperature ($T_g$) and conversion (${\alpha}$) were measured for a diglycidyl ether of bisphenol A (DGEBA) epoxy/aromatic amine system incorporated with an organic-inorganic hybrid molecule, polyhedral oligomeric silsesquioxane (POSS). Samples isothermally cured at varying cure temperatures and times were analyzed by differential scanning calorimetry (DSC). $T_g$ vs. ln (time) data at an arbitrary reference were superposed by time-temperature shifts for the kinetically controlled reaction, and the shift factors were used to calculate an Arrhenius activation energy. Influence of POSS was investigated from $T_g$ vs. ${\alpha}$ data, which in turn were fitted with DiBenedetto equation.

• Polymer(Korea)
• /
• v.24 no.3
• /
• pp.399-406
• /
• 2000

A thermotropic liquid crystalline polymer (TLCP) containing a flexible spacer was synthesized from hydroquinone, p-hydrofybenzoic acid, and 1,6-dibromohexane. Intercalation of TLCP in layered clays is accomplished by heating the polymer with dodecyl ammonium-montmorillonite (C$_{12}$-MMT) above melt transition temperature (T$_{m}$). Liquid crystallinity of the TLCP/C$_{12}$-MMT hybrid was not observed when $C_{12}$-MMT content was above 1 wt%. Some of the $C_{12}$-MMTs in TLCP were highly dispersed in a nanometer scale, but some of them were agglomerated. Thermal and morphological properties of the nanocomposites were examined by differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), polarized optical microscope, and electron microscopes (SEM and TEM). TEM).

• Korean Journal of Optics and Photonics
• /
• v.22 no.2
• /
• pp.102-107
• /
• 2011

In this paper, a small double ring resonator reflector was designed and fabricated using a polymer waveguide, and the measurement result was discussed. A widely tunable characteristic of the small double ring resonator caused by the Vernier effect, which results from the difference of the ring radii, was observed. The insertion loss of the double ring reflector was reduced by minimizing the device length to be as short as possible, and thus the output power and the SMSR (side mode suppression ratio) was greatly enhanced. The hybrid integrated laser based on the small double ring resonator reflector lased with the SMSR of 45 dB. In addition, the wide tuning range of 40 nm could be obtained by injecting a current of 30 mA to an electrode on top of the reflector.

• Polymer(Korea)
• /
• v.38 no.5
• /
• pp.573-579
• /
• 2014

The effect of synthesis conditions such as carbon nanotube (CNT), 2,2,2-trifluoroethylmethacrylate (3FMA), and composition of organic-inorganic material in ozone resistance and surface characteristics of ultraviolet cured organic-inorganic hybrid coating film has been investigated. Coating solution was prepared using tetraethoxysilane (TEOS), silane coupling agent methacryloyloxypropyltrimethoxysilane (MPTMS), 3FMA, various organic materials with acrylate group, and CNT, then bar-coated on substrates using applicator, and densified by UV-curing. It was found that ozone resistance and adhesion of the coating film were strongly dependent upon contents of TEOS, 3FMA, and CNT. Especially, ozone resistance, adhesion, and surface hardness of coating film with CNT were improved, relatively. Ozone resistance of coating film with a high TEOS content was increased, but adhesion was decreased. In addition, it was also found that ozone resistance of coating film was increased with contents of 3FMA. On the other hand, surface hardness was decreased with increase of 3FMA.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.299-299
• /
• 2013

Indium Tin Oxide (ITO) has widely been used as a transparent conductive oxide (TCE) for photovoltaic devices. Lately, flexibility of ITO becomes an issue as demand of flexible device increases. Several scientists have tried to substitute ITO to different materials such as conductive polymer, graphene, CNT, and metal nanowire because of ITO brittleness. Among the substitute materials, PEDOT:PSS has mostly paid attention because PEDOT:PSS has excellent flexibility and good conductivity. The conductivity of PEDOT:PSS increases up to 1000 S/cm with additives such as DMSO, EG, sorbitol, and so on. In our research group, we introduce a conductive polymer PEDOT:PSS as a buffer layer to improve not only flexibility but also conductivity. As PEDOT:PSS layer forms beneath ITO thin film (20 nm), sheet resistance decreases from $230{\Omega}$/${\Box}$ to $85{\Omega}$/${\Box}$ and crack initiation decreases from 4.5 mm to 3.5 mm as well. We have fabricated organic photovoltaic device and power conversion efficiencies using conventional ITO electrode and ITO/PEDOT:PSS hybrid electrode. The photovoltaic property such as power conversion efficiency for ITO/PEDOT:PSS hybrid electrode is comparable to the value obtained using conventional ITO electrode on glass substrate.

• Polymer(Korea)
• /
• v.27 no.1
• /
• pp.61-68
• /
• 2003

In this study, we have investigated the preparation of mixed bead and fiber type hybrid ion-exchanger for recovering nickel ion from plating rinse water. There was little dependence of adsorption capacity for nickel ion on the mixing ratio of resin type and fiber type of ion exchangers. However, it increased with increasing the resin content in the mixed bed. It was shown that the data Langmuir and Freundlich's adsorption isotherm model were well fitted to the linear. Affinity between the functional groups in the ion exchanger and nickel ion in the process was confirmed. The pressure drop decreased with increasing the number of stage in the multistage bed, but it increased with increasing the resin content in the mixing bed. The initial breakthrough time in the multistage bed was short due to the increase of number of stage in the continuous process. It was found that the final breakthrough time of the multistage bed was little changed. The breakthrough time decreased with increasing the amount of fibrous ion exchanger in the mixed bed. The maximum adsorption capacities of the mixed and multistage beds were 2.51 meq/g and 2.69 meq/g, respectively. The desorption time for the nickel ion with $1N H_2SO_4$ solution was lower than 10 minutes and the yield of desorption was greater than 98 percent.

• Macromolecular Research
• /
• v.15 no.5
• /
• pp.412-417
• /
• 2007

In the present study, crosslinked poly(vinyl alcohol) (PVA) membranes were prepared at different temperatures using poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA) (PVA:PSSA_MA = 1:9). The hybrid mem-branes were prepared by varying the TEOS content between 5 and 30 wt%. The PSSA_MA was used both as a crosslinking agent and the hydrophilic group donor ($-SO_3H$ and/or-COOH). The proton conductivity increased with up to 20 wt% TEOS, but decreased above this level, although the water content decreased with increasing TEOS content. This result suggests that the silica doped into the membrane improved the formation of proton-conduction pathways due to the absorption of molecular water. The PVA/PSSA_MA/Silica containing TEOS 20% showed both high proton conductivity (0.026 S/cm at $90^{\circ}C$) and low methanol permeability ($5.55{\times}10^{-7}cm^2/s$).