• Korean Chemical Engineering Research
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• v.56 no.2
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• pp.162-168
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• 2018

UV-curable hard coating solutions were prepared by mixing organic or inorganic polysilazane with urethane acrylate. UV-cured hard coating films were also obtained by flow coating, subsequently UV-curing on polymethylmethacrylate (PMMA) sheets. The effect of types and amounts of polysilazane was investigated on properties of obtained coating films. As a result, the coatings obtained by using organic polysilazane showed a high hydrophobic property with water contact angle of $95^{\circ}$, pencil hardness of 7H and high transparency of 92% in the visible wavelength range. On the other hand, the PMMA sheets made by using inorganic polysilazane exhibited a pencil hardness of as high as 8H, good adhesion to the substrate and water contact angle of $82^{\circ}$.

• Macromolecular Research
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• v.14 no.2
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• pp.220-229
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• 2006

Several equations of state for hard-sphere chains with various perturbation terms are reviewed. For each model, three characteristic parameters are required to represent phase equilibria of normal fluids and obtained from thermodynamic properties of pure saturated liquids. The models are then compared with computer simulation data to show the effect of attractive contribution forms employed. Calculated values of vapor-liquid equilibria (VLE) of hydrocarbons that can be reproduced for each model are also compared with experimental results. An additional parameter, ${\zeta}_{KB}$, is required to represent the VLE of pure water, which is ascertained to have a strong influence on the theoretical coexistence curve.

• Elastomers and Composites
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• v.34 no.4
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• pp.285-291
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• 1999

Effects of catalysts on network structure, hard segment length and distribution of polyurethane foams in the absence of catalysts were investigated. CFC free all MDI-based poly urethane foams were prepared from poly(ethylene adipate)glycol, 4,4'-diphenylmethane diisocyanate, and water. Amino catalysts used were 1,4-diazabicyclo[2,2,2]octane(DABCO), N, N,N',N'-tetramethyl--hexane-1,6-diamine(MR), bis(2-methylamino ethyl)ether(ET), 1,8-diazabicyclo-[5,4,0]-undecene-7(DBU). Dibutyltindilaurate(DBTL) as control was also used. Hard segment components of polyurethane foams were obtained by a selective degradation of polyester chains with 0.01N KOH-methanol solution. The PUFs with DBU catalyst contained more amount of isocyanurate components than other PUFs. On the other hand, the PUFs with ET, MR, DBTL catalysts contained more amount of allophanate and biuret component than the other PUFs.

• Proceedings of the Membrane Society of Korea Conference
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• 1999.10b
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• pp.23-26
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• 1999

• Water Engineering Research
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• v.2 no.2
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• pp.103-112
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• 2001

Issues and problems in formulating South Korea's water resources policy are discussed in terms of water quantity and quality. South Korean needs both water conservation and water supply capability for the growing population and economic activities. The government has attempted to build more large-scale dams to store and supply water for residential, farming and industrial uses, but the environmentalists who emphasize conservation and environmental protection oppose the government. The environmentalists are popular among the general public. Water quality has been deteriorating from point- ad non-point sources. urban and farm runoffs are serious pollutants. All want by preserve water quality. There is no dispute on this matter between the government and the environmentalists. Money is hard to come by to preserve water quality. Economic and financial crises and no self-sufficient local governments' revenue structure are pessimistic. Basic survey on water resources, hydrology and hydraulic is badly needed for the future water resources planning.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.444-448
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• 2007

The effects of intra-particle composition on the adhesive properties and water dispersity of acrylic emulsion type pressure sensitive adhesives (PSAs) were investigated. In the case of PSA having uniform intra-particle composition, the higher holding strength made the water dispersity lower. By changing the intra-particle composition in hard core/soft shell type, however, it was possible to get PSAs showing both high holding strength and water dispersity. When the weight ratio of MAA/AA is 4/1, high holding strength, but low initial tack and very low water dispersity were observed in both cases of higher contents of (AA+MAA) in core and shell area. When the weight ratio of MAA/AA is 1/4, however, higher water dispersity and lower holding strength were indicated in the case of higher contents of (AA+MAA) in shell area.

• Journal of Biomedical Engineering Research
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• v.20 no.2
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• pp.231-236
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• 1999

Understanding the exgenous water induced thermomechanical effect on the dental hard tissue by the Q-switched Er:YAG laser (1-$mutextrm{s}$-long pulse width) has an important impact on the further understanding of the free-running Er:YAG laser (250-$mutextrm{s}$-long pulse width) ablation on the dental gard tissue because one macroscopic effect in the free-running laser is an accumulation of microscopic effects we investigated in this study. The Q-switched Er:YAG laser with exogenous water on the tooth enhanced ablation rate compared to the case of no water on the tooth. The frequency of exogenous-water jet on the tooth has affected the ablation rate in such a way that as we dispensed water drops less frequently we could get more enhanced ablation rate. The amplitude of the recoil pressure depends on the tooth surface conditions such that as surfaces wet, and as the volume of the exogenous water drop increased, the amplitude of the recoil pressure increased also. From this study we realized that the 1 $mutextrm{s}$ long pulsed induced thermomechanical effect provides us useful information for the understanding of the free-running Er:YAG laser induced ablation with exogenous water.

• The Journal of the Korean dental association
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• v.56 no.7
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• pp.385-390
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• 2018

Laser means "Light amplification by stimulated emission of radiation". Laser have unique characteristics according to wavelength. Wavelenth of Waterlase is 2780nm and it can be absorbed to water and hydroxyapatite. When laser is applied to some material, its temperature goes up due to laser's energy. But in dental treatment high temperature is not good for teeth. High temperature can make dental pulp and bone necrosis. Waterlase can be absorbed to water droplet, so when it burst, it can cut soft and hard tissue without raising temperature. so it is so proper to dental treatment.

• Preventive Nutrition and Food Science
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• v.11 no.3
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• pp.243-252
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• 2006

White salted noodles and pan bread were prepared from Korean wheats with 1Dx2.2+1Dy12 subunits in high molecular weight glutenin subunits (HMW-GS) to evaluate the suitability for end-use products through the comparison with US wheats with various classes and commercial wheat flours. Korean wheat flours with 1Dx2.2+1Dy12 subunits showed higher SDS sedimentation volume than US wheat flours with similar protein content. Compared to wheat flours with similar protein content and SDS sedimentation volume, water absorption percent of Korean wheat flours using a mixograph was higher than that of US wheat flours, but similar to commercial wheat flours. Mixograph mixing time was similar to hard wheat flours and commercial noodle flours. Optimum water absorption percent of noodle dough from Korean wheat flours was higher than that of US wheat flours. Noodle sheets from Korean wheat flours with 1Dx2.2+ 1Dy12 subunits showed lower L values, higher a values and similar b values compared to commercial noodle flours. Hardness of cooked noodles from Korean wheat flours 1Dx2.2+1Dy12 subunits correlated positively with protein content, NIRS hardness, mixograph water absorption and gluten yield of flours. Korean wheat flours with 1Dx2.2+1Dy12 subunits showed lower loaf volume and harder crumb firmness than hard wheat flours and commercial bread wheat flours in spite of similar protein quantity and quality to hard wheat flours.

• Macromolecular Research
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• v.10 no.6
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• pp.325-331
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• 2002

Phase behavior of a PEO-PPO-PEO (Pluronic P103) triblock copolymer in water is investigated using small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), dynamic light scattering (DLS) and rheology. Pluronic P103 shows apparent two gel states in different temperature regions. The first sol-to-gel transition at a lower temperature (i.e., the hard gel I state) turns out to be the hexagonal microphase as evidenced by the combined SANS and SAXS and the frequency dependence of both G′ and G" in rheology. In contrast to the hard gel I, the second sol-to-gel transition (i. e., the hard gel II state) at a higher temperature represents the block copolymer micelles in somewhat disordered state rather than the ordered state seen in the hard gel I. Moreover, turbidity change depending only on the temperature with four distinct regions is observed and the large aggregates with size larger than 5,000 nm are detected with DLS in the turbid solution region. Based upon the present study, two different gelation mechanisms for aqueous PEO-PPO-PEO triblock copolymer solutions are proposed.