• Polymer(Korea)
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• v.35 no.1
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• pp.52-59
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• 2011

L-PLA or D-PLA was synthesized in bulk at $140^{\circ}C$ by ring opening polymerization(ROP) of L-lactide or D-lactide as a monomer using tin(II) octoate and lauryl alcohol as a catalyst and an initiator with changing the amounts of catalyst(0.25~1.0 wt%) and initiator(0.l~0.5 wt%). And stereocomplex-PLA was prepared by L-PLA/D-PLA having a wide range of molecular weight(30000~90000 g/mol) and L-PLA/D-PLA blends having different mixing ratio ($X_D$). The melting temperature. thermal degradation temperature and thermal stability of stereocomplex-PLA were higher than those of homopolymers(L-PLA, D-PLA). We supposed that these improvements arose from a strong interaction between L-PLA and D-PLA. The improved mechanical properties and changes in morphology of LPLA/D-PLA blends were compared to those of homopolymers(L-PLA, D-PLA).

• Journal of the Society of Cosmetic Scientists of Korea
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• v.41 no.3
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• pp.209-218
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• 2015

Once powder base makeup products are applied to the skin, the products are formed a film and attached on the skin for 8 to 12 hours. The makeup film is deformed by secretions such as sweat and sebum secreted from the skin. Thus, durability of the film is an important quality factor in the makeup and its evaluation is also important. In this study, characteristics of the semi-finished powder products such as water absorption, oil absorption, water repellent and oil repellent were evaluated in a number of ways. Also, simple methods, which are not affected by evaluation conditions such as a difference between sweat and sebum secretion, temperature and humidity, were examined to predict the durability of the products. We measured water absorption, oil absorption, water repellent and oil-repellent properties of semifinished product by tablet, capillary and dipping method and then compared with the data of color difference meter and ROBO skin analyzer. Results showed that the durability of powder base makeup products was associated with more oil absorption and water-repellent characteristics than water absorption and oil-repellent. Oil absorption characteristics by tablet and capillary method and water-repellent characteristics by dipping method provides a simple and quick method to precdict the durability of the makeup products.

• Korean Journal of Environment and Ecology
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• v.29 no.3
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• pp.410-420
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• 2015

In order to estimate the influence of environmental factors on zooplankton communities in lentic freshwater ecosystems, 20 reservoirs and wetlands were monitored by season in 2013. A total of 109 species of zooplankton were identified during the study period. Zooplankton assemblage showed a different distribution in its density and diversity in accordance with the seasons. In particular, the density of zooplankton (98 species and 603ind. L-1) was the most in autumn when compared to the other seasons. In order to effectively analyze zooplankton distribution that are affected by various environmental factors, a Self-Organizing Map (SOM) was used, which extracts information through competitive and adaptive properties. A total of 11 variables (8 environment factors and 3 groups of zooplankton) were patterned on to the SOM. Based on a U-matrix, four clusters were identified from the model. Among zooplankton communities, rotifer displayed a positive relationship with water temperature, and cladocerans and copepod were positively related to conductivity, chlorophyll a, and nutrient factor (i. e. TN and TP). In contrast, high dissolved oxygen appeared to have a negative effect on zooplankton distribution. Consequently, the SOM results depicted a clear pattern of zooplankton density clusters partitioned by environmental factors, which play a key role in determining the seasonal distribution of zooplankton groups in lentic freshwater ecosystem.

• Journal of the Korean Chemical Society
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• v.54 no.4
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• pp.395-401
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• 2010

A series of macrocyclic complexes of the type [M(L/L')$(NO_3)_n$].$mH_2O$ and [VO(L/L')($SO_4$)].$2H_2O$, where L/L' is a Schiff base "3,4,10,11-tetraphenyl/tetramethyl-1,2,5,6,8,9,12,13-octaaza cyclotetradeca-2,4,9,11-tetraene-7,14-dithione" derived from thiocarbohydrazide (TCH), benzilmonohydrazone (BMH)/diacetylmonohydrazone (DMH) and carbon disulphide, M = $UO_2$ (VI), Th(IV) and ZrO(IV), n = 2, 4, m = 2, 3, have been synthesized via metal ion template methods. The complexes are characterized on the basis of elemental analysis, thermal analysis, molar conductivity, magnetic moment, electronic, infrared and $^1H$-NMR spectral studies. The ESR and cyclic voltammetry studies of the vanadyl complexes have been carried out. The results indicate that the VO(IV) ion is penta-coordinated yielding paramagnetic complexes; $UO_2$(VI) and ZrO(IV) ions are hexacoordinated where as Th(IV) ion is octa-coordinated yielding diamagnetic complexes of above composition.

• Clean Technology
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• v.17 no.4
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• pp.395-405
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• 2011

To develop the technology for cultivation of high-density seaweed, sea tangle was cultured from varying depths(0.5 m, 3 m) of seawater at Gijang and Wando area. Proximate composition, component sugar, total amino acid, fatty acid composition, and element composition of different parts of sea tangle (Saccharina japonica) have been examined. Significant differences were found in the amount of crude protein and ash content in lower, middle, and upper parts of algal blades. The upper parts of the sea tangle was rich in crude protein, while lower parts was rich in crude ash. Crude lipid content was higher in the middle parts than those of the other parts. The component sugars were not significantly different from all parts of algal blades. The highest content of most of the amino acids were found in the upper parts of the blades. The amount of saturated fatty acids concentrated mostly in lower parts of blades, while the content of polyunsaturated fatty acids concentrated in the upper parts. The highest N element contents were found in upper part of algal blades. However, the contents of those chemical component were not affected by the depths of seawater.

• Clean Technology
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• v.24 no.3
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• pp.175-182
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• 2018

In this research, we investigated the cleanliness by optimizing the water content of the aqueous stripper in fluidic strip process. The stripping properties of the photoresist with optimized aqueous stripper were compared with the commercial organic stripper. The stripping performance was evaluated by electrical and optical characteristics on the surface of the transparent electrode that compare with stripped the transparent electrode surface and the rare surface before patterning by the photoresist. As a result of the photoresist stripping process of the organic stripper and the aqueous stripper optimized for water content, the aqueous stripper exhibited better electrical and optical characteristics than the organic stripper. In the case of the fluidic strip process with organic stripper, the photoresist dissolves in the stripper solution during stripping which can cause re-adsorption by contamination. Whereas that the aqueous stripper under development seems to decrease the photoresist dissolution in the stripper solution. Because the cyclodextrin contained in the stripper captures organic photoresist into hall of cyclodextrin which stripped through swelling and tearing. The photoresist residue captured by the cyclodextrin can be filtered. After the fluidic stripping process by different chemical stripping mechanism, the cleanliness of the organic stripper and aqueous stripper was compared and analyzed.

• Korean Journal of Agricultural Science
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• v.13 no.2
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• pp.255-264
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• 1986

The objectives of this study were to examine the viscoelastic behaviour of stem samples of rice in force-relaxation and rheological model to represent its relaxation behaviour, and to study the effects of rate of deformation and initial deformation on the relaxation time. The results were as follows; 1. In the process of loading and unloading, there is any plastic deformation so called elasto-plastic hysterisis. 2. Loading and unloading of stem of rice for several cycles has also shown the reduction of plastic or residual deformation and work hardening. 3. The relaxation behaviour of stem of rice in compression may be described by a generalized Maxwell model consisting of three Maxwell units in parallel. The rheological equation of such a model is given as $$F(t)=C_1e^{{-t/{\tau}}_1}+C_2e^{{-t/{\tau}}_2}+C_3e^{{-t/{\tau}}_3}$$ 4. Force relaxation always increased with increasing rates of deformation and initial deformation.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.505-512
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• 2014

A new donor-accepter-donor-accepter-donor (D-A-D-A-D) type 2,1,3-benzothiadiazole-thiophene-based acceptor unit 2,5-di(4-(5-bromo-4-octylthiophen-2-yl)-2,1,3-benzothiadiazol-7-yl)thiophene ($DTBTTBr_2$) was synthesized. Copolymerized with fluorene and indeno[1,2-b]fluorene electron-rich moieties, two alternating narrow band gap (NBG) copolymers PF-DTBTT and PIF-DTBTT were prepared. And two copolymers exhibit broad and strong absorption in the range of 300-700 nm with optical band gap of about 1.75 eV. The highest occupied molecular orbital (HOMO) energy levels vary between -5.43 and -5.52 eV and the lowest unoccupied molecular orbital (LUMO) energy levels range from -3.64 to -3.77 eV. Potential applications of the copolymers as electron donor material and $PC_{71}BM$ ([6,6]-phenyl-$C_{71}$ butyric acid methyl ester) as electron acceptors were investigated for photovoltaic solar cells (PSCs). Photovoltaic performances based on the blend of PF-DTBTT/$PC_{71}BM$ (w:w; 1:2) and PIF-DTBTT/$PC_{71}BM$ (w:w; 1:2) with devices configuration as ITO/PEDOT: PSS/blend/Ca/Al, show an incident photon-to-current conversion efficiency (IPCE) of 2.34% and 2.56% with the open circuit voltage ($V_{oc}$) of 0.87 V and 0.90 V, short circuit current density ($J_{sc}$) of $6.02mA/cm^2$ and $6.12mA/cm^2$ under an AM1.5 simulator ($100mA/cm^2$). The photocurrent responses exhibit the onset wavelength extending up to 720 nm. These results indicate that the resulted narrow band gap copolymers are viable electron donor materials for polymer solar cells.

• Korean Journal of Materials Research
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• v.10 no.12
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• pp.807-811
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• 2000

CeO$_2$ and SrBi$_2$Ta$_2$O$_{9}$ (SBT) thin films for MFISFET (Metal-ferroelectric-insulator-semiconductor-field effect transistor) were deposited by r.f. sputtering and pulsed laser ablation method, respectively. The effects of sputtering gas ratio(Ar:O$_2$) during deposition for CeO$_2$ films were investigated. The CeO$_2$ thin films deposited on Si(100) substrate at $600^{\circ}C$ exhibited (200) preferred orientation. The preferred orientation, Brain size and surface roughness of films decreased with increasing oxygen to argon gas ratio. The films deposited under the condition of Ar:O$_2$= 1 : 1 showed the best C- V characteristics. The leakage current of films showed the order of 10$^{-7}$ ~10$^{-8}$ A at 100kV/cm. The SBT thin films on CeO$_2$/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure with SBT film annealed at 80$0^{\circ}C$, the memory window width was 0.9V at 5V The leakage current density of Pt/SBT/CeO$_2$/Si structure annealed at 80$0^{\circ}C$ was 4$\times$10$^{-7}$ /$\textrm{cm}^2$ at 5V.

• Polymer(Korea)
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• v.30 no.6
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• pp.538-544
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• 2006

Two kinds of novel bifunctional methacrylated prepolymers (170-2MA and 631-2MA) which have similar structure with 2,2-bis[4- (2'-hynroxy-3'-methacryloyloxypropoxy)phenyl] propane (Bis-GMA) was synthesized for dental applications as an alternative to Bis-GMA containing bisphenol A that is doubtful as an endocrine disrupter. The organic matrices were prepared by mixing a diluent and/or a monomer with the synthesized methacrylated prepolymers. The yield, viscosity, and chemical structures of the prepolymers and the physical and methanical properties of the organic matrices were evaluated. The yields of the prepolymers synthesized through a ring-opening reaction of epoxy compound and methacrylic acid were above 90% and the viscosities of the prepolymers were much lower than that of the Bis-GMA control. From the results of $^1H-NMR$ and FTIR analyses, the chemical structures of the prepolymers were similar to that of Bis-GMA. In addition, the curing time, poly-merization shrinkage, photoconversion, polymerization depth, and compressive strength of the organic matrices formulated with 170-2MA and 631-2MA prepolymers exhibited comparable to or better than those of the existing Bis-GMA-based one. These results suggest that the novel methacrylated prepolymers which have no endocrine disrupter can be an alternative to Bis-GMA and be applicable to dental polymer materials.