• Analytical Science and Technology
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• v.26 no.1
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• pp.19-26
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• 2013

Gibberllic acid ($GA_3$) is one of gibberellins (GAs) that are a class of plant growth hormones that exert profound and diverse effects on plant growth and development. $GA_3$ is essentially non-UV absorbing and is difficult to assay by UV-detector. For effective extraction of gibberellic acid from fruits by using liquid-liquid extraction, optimized pH and extraction solvent were established. The selective and sensitive derivative of $GA_3$ for HPLC/UV-vis was derivatized using phenacyl bromide, and the experimental factors, including reaction time, reaction temperature and amount of derivatizing reagent and base were investigated for the effective synthesis. The derivatized $GA_3$ with phenacyl bromide was effectively analyzed by HPLC/UV-vis. The structure of derivatized $GA_3$ was confirmed by HPLC/ESI-MS. For apple, LOD and LOQ were 0.008 mg/kg and 0.027 mg/kg, respectively. For pear, LOD and LOQ were 0.003 mg/kg, 0.012 mg/kg, respectively. The established method can be applied to more effective analysis of $GA_3$ from plant and food.

• Polymer(Korea)
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• v.35 no.2
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• pp.183-188
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• 2011

Pentaerytritol triacrylate (PETA) was synthesized by a condensation reaction between pentaerytritol and acrylic acid. The highest yield of PETA was obtained when heptane was used as a solvent under the 1:4 mole ratio of pentaerytritol and acrylic acid. The 6-functional urethane acrylates(UA) were also synthesized by a condensation reaction between PETA and diisocyanate. Cured films were prepared from the mixtures of UA oligomer, reactive diluents and UV initiator to investigate their physical properties. The thermal stability of the aliphatic urethane acrylate was better than that of the aromatic urethane acrylate. The UA-2 showed good hardness and scratch resistance properties while the UA-l with a high degree of curing density exhibited a better chemical resistance. All the UA oligomers showed fairly good adhesion strengths but the other physical properties of UA-3 were poor due to its low curing density.

• Polymer(Korea)
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• v.29 no.1
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• pp.25-31
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• 2005

Cellulose acetate derivatives containing 6-(p-hexyloxyphenyl)carbonyl spirobenzopyran (CA-COSP) were prepared from base-catalyzed etherification of cellulose acetate, and their physical and photochromic properties were characterized. The degree of substitution of COSP was calculated from the amount of residual hydroxyl groups in cellulose acetate measured by the $^1H$-NMR and UV spectrometric data. It was ranging from 0.87 to 45.5% depending on the reaction condition. UV/vis spectrometry of the resulting CA-COSP revealed that the polymer shows a reversible color change by changing its color from colorless to blue upon UV irradiation forming a merocyanine structure, and returning back again to colorless spiropyran structure by visible light or by heat. The rate of color change was faster in solution than in the film. In the more polar solvent, the more stable was the resulting merocyanine, and the slower was the rate of reverse reaction to spiropyran. Compared to COSP blended with cellulose acetate, in which a phase separation was observed for samples containing more than 0.9 wt% of COSP, up to 48 wt% of COSP could be blended in CA-COSP without phase separation.

• Polymer(Korea)
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• v.26 no.6
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• pp.701-709
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• 2002

To synthesize a new positive photosensitive polyimide precursor, parts of carboxylic acid groups in poly (amic acid) were esterified with 4,5-dimethoxy-2-nitrobenzyl bromide in the presence of K$_2$CO$_3$/HMPA followed by the chemical imidization of residual carboxylic acid units. The chemical structure of resulting polymer was characterized by $^1$H-NMR, UV/vis and FT-IR spectroscopic methods, and its thermal properties were examined by DSC and TGA. Upon UV irradiation, 4,5-dimethoxy-2-nitrobenzyl moiety underwent the photodegradation. As a result, the polymer became soluble in alkaline developer due to the formation of carboxylic acid moiety, which was used to make a micron-sized positive pattern. Sensitivity curves were obtained from the gel fraction experiments with respect to the various 4,5-dimethoxy-2-nitrobenzyl ester contents. From those curves, the sensitivity was ranged iron 4000 to 6000 mJ/㎠, and the contrast was measured to be from 3.1 to 4.9.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.355-360
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• 2006

The Alkali-Silica Reaction(ASR) may cause a serious failure in the concrete pavements and structures. Several researches in some nations have conducted the continuous studies to prevent failure of the concrete structures by the ASR distress as well as the studies to manifest the mechanism. The researches on the ASR have not been performed affluently in Korea because the distress due to ASR has seldom been reported literarily. In this study, we tried to set up the systematic scheme practically for verifying the cause of distress due to ASR by using the visual inspections in field, the chemical method, petrographic analysis, and Electron Dispersive X-ray Spectrometer(EDX) method of Scanning Electron Microscopy(SEM) in laboratory. The chemical method, petrographic method using SEM, and X-ray method were used to verify the cause of pattern crack on the surface and internal crack in the plain concrete pavement. It can be concluded that the distress of a specific site in plain concrete pavement was mainly due to ASR. The chemical method, the petrographic method and EDX method using SEM may be the effective tools for verifying the cause of AAR distresses.

• Polymer(Korea)
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• v.38 no.2
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• pp.138-143
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• 2014

${\alpha},{\omega}$-Hydroxypropyl polydimethylsiloxane (HO-PDMS) was prepared by hydrosilylation of hydrogen terminated polydimethylsiloxane with allyl alcohol. Polydimethylsiloxane modified urethane with isocyanate group (PSU) was prepared from cyclic trimer of hexamethylenediisocyanate with HO-PDMS. PDMS modified urethane base resin with acrylic group (PSUA) was prepared from the urethane reaction of PSU with isocyanate group and 2-hydroxyethylmethacrylate. Their structures were characterized using FTIR and NMR. Coating materials were prepared by mixing PSUA, acrylic hardner, photo-initiator, and solvent and coated on PET film to obtain flexible and hard coating film by UV irradiation. Transparency of coating film was 89.7%, contact angle, $88^{\circ}$, and pencil hardness, 3H.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.287-292
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• 2010

We have investigated the effects of oxygen flow ratios on the structural, morphological, and optical properties of AlN thin films grown by using radio-frequency reactive magnetron sputtering. The AlN thin films were deposited at $300^{\circ}C$ of substrate temperature, and the reactive gas were supplied with both nitrogen and oxygen. The oxygen flow ratio was varied by controlling the amount of oxygen with respect to the total mixed gases, 0%, 10%, 15%, 20%, 25%, and 30%. The structural, morphological, and optical properties of the deposited AlN thin films were examined by using X-ray diffractometer, scanning electron microscopy, and ultraviolet-visible spectrophotometer. The AlN thin film grown at 10% of oxygen flow ratio indicated an average transmittance of 91.3% in the wavelength range of 350~1,100 nm and an optical band gap of 4.30 eV. The experimental results suggest that AlN thin films can be deposited optionally by varying the oxygen flow ratio.

• Journal of Aquaculture
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• v.17 no.2
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• pp.97-102
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• 2004

We examined the effects of stimulants including sunlight and UV-irradiation on the spawning induction and early development of the noble scallop, Chlamys nobilis. The sunlight stimulation resulted in nuch faster spawning induction (100% success within 40 minutes) compared to UV-irradiation (100% success within 70 minutes). Early development of the scallop larva took place between 15$^{\circ}C$ to 3$0^{\circ}C$. The time to reach the early D-shaped stage was 63.5, 31.5, 18.5 and 17.0 hours at 15, 20, 25 and 3$0^{\circ}C$, respectively. The correlations between the water temperature-(WT) regimes and the time (t) required for each developmental stage are as follows. 2 cell stage: 1/t=0.0606WT-0.6194 ($r^2$=0.9791) 8 cell stage: 1/t=0.0304WT-0.3453 ($r^2$=0.9941) Morula: 1/t=0.0100WT-0.1049 ($r^2$=0.9663) Trochophore: 1/t=0.0058WT-0.0618 ($r^2$=0.9848) D-shaped larva: 1/t=0.0030WT-0.0282 ($r^2$=0.9731) These correlations indicated that the biological minimum temperature of the species is around 10.44$^{\circ}C$. The highest survival rate up to D-shaped larva at different water temperature was observed at $25^{\circ}C$.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.80-84
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• 2005

Nano-sized $Y_2O_3:Eu$ phosphor particles were prepared by ultrasonic spray pyrolysis. The effect of polymeric precursor and lithium carbonate flux on the morphology and luminescence characteristics of nano-sized $Y_2O_3:Eu$ phosphor particles was investigated. When using the spray solution containing both the polymeric precursor and the flux, the $Y_2O_3:Eu$ particles with spherical shape and micron size were turned into nano-sized $Y_2O_3:Eu$ phosphor particles during the post-treatment at high temperature. The mean size of $Y_2O_3:Eu$ phosphor particles was affected by the contents of polymeric precursors and lithium carbonate flux, and preparation temperature. The as-prepared particles by spray pyrolysis at high temperature from solution containing high contents of polymeric precursors had good photoluminescence intensity under vacuum ultraviolet after post-treatment above $1,000^{\circ}C$. The prepared nano-sized $Y_2O_3:Eu$ phosphor particles had comparable photoluminescence intensity under vacuum ultraviolet light with that of the commercial $Y_2O_3:Eu$ phosphor particles prepared by solid state reaction method.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.28-32
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• 1998

Two organophosphorous insecticides, Dichlorovos and Chloropyrifos were degraded in the presence of UV irradiation, UV irradiation with $TiO_2$ powder and UV irradiation with sea sand using low pressure mercury lamp. The identification of these compounds was carried out by gas chromatograph with a nitrogen-phosphorous detector, Total Organic Carbon and Ion Chromatograph, respectively. Both dichlorvos and chloropyrifos, UV irradiation with sea sand were more degradable than UV irradiation and UV irradiation with $TiO_2$ powder. The final products were $Cl^-$ in Dichlorvos, $Cl^-$ $SO_4{^{2-}}$ in Chloropyrifos, respectively.