• Bulletin of the Korean Chemical Society
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• v.27 no.12
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• pp.1981-1984
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• 2006

Novel amphiphilic, thermo-responsive polyaspartamides which showed both LCST (lower critical solution temperature), and sol-gel transition were prepared and characterized. The polyaspartamide derivatives were synthesized from polysuccinimide, the polycondensate of aspartic acid monomer, via successive nucleophilic ring-opening reaction by using dodecylamine and N-isopropylethylenediamine (NIPEDA). At the intermediate composition ranges, the dilute aqueous solution exhibited a thermally responsive phase separation due to the presence of LCST. The phase transition temperature was controllable by changing the content of pendent groups. In addition, a physical gelation, i.e. the sol-gel transition was observed from the concentrated solutions, which was elucidated by dynamic viscoelastic measurements. These novel injectable and thermo-responsive hydrogels have potential for various biomedical applications such as tissue engineering and current drug delivery system.

• Journal of the Korean Ceramic Society
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• v.28 no.12
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• pp.1012-1018
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• 1991

SiC whisker-reinforced LAS matrix composites were developed by a mixed colloidal processing route. An optimization of processing conditions was made using the zeta potential data of silica, boehmite, and SiC whisker dispersions. Similarly, the SiC whisker-reinforced composites were also fabricated by the conventional sol-gel process using the hydrolysis-condensation reaction of relevant metal alkoxides. The composites fabricated by the mixed colloidal processing route were characterized by a uniform spatial distribution of SiC whisker throughout the matrix. The fracture toughness increased from 1.3 MPa.m1/2 for the LAS specimen to 5.0 Mpa.m1/2 for the hot-pressed composite (95$0^{\circ}C$ and 20 MPa for 20 min) containing 20 wt% SiC whisker. The increase in fracture toughness appears to result mainly from the crack deflection and the crack bridging by whiskers with some additional toughenings from the whisker pullout and the matrix prestressing mechanisms.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.66-67
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• 2020

The synthesis of stearic acid composite phase change material (PCM) was investigated and the samples produced were characterized for use in latent heat storage, using a simple chemical sol-gel process. The PCM was encapsulated to tetraethyl orthosilicate by various preparation ratios of stearic acid (5, 10, 15, 20, 30 and 50%). Fourier transformation infrared spectroscope (FT-IR) and X-Ray diffraction (XRD) were performed to determine the chemical structure and crystalloid phase of the microencapsulated PCM. SATEOS1 (5%) shows the best proportion for the PCM. With the presence of stearic acid as core materials and SiO2 as the supporting materials, it does not show any chemical reaction between both of them. SATEOS1 shows promising potential for thermal energy storage as it shows a better encapsulation efficiency and good thermal stability.

• Transactions on Electrical and Electronic Materials
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• v.12 no.5
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• pp.222-225
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• 2011

Lead zirconate titanate (PZT) films were fabricated on Pt/Ti/$SiO_2$/Si substrate by the sol-gel method using a sol containing poly(N-vinylpyrrolidone) (PVP). PVP in alkoxide solutions can suppress the condensation reaction in gel films during heat treatment, and increase the viscosity of alkoxide solutions. Single-phase PZT films as thick as 1 ${\mu}m$ were deposited by repetitive coating with successive third-step heat treatments at 150$^{\circ}C$, 350$^{\circ}C$ and 650$^{\circ}C$. After heat treatment, the films were crack free, and optically transparent. As a result, we demonstrated a PZT film with a PVP molar ratio of 0.5, which has a permittivity of 734, a dielectric loss of 0.042, a $P_r$ of 40.5 ${\mu}C/cm^2$ and an $E_c$ of 156 kV/cm.

• Korean Journal of Materials Research
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• v.14 no.10
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• pp.749-753
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• 2004

In this study, we attempt to synthesize the $Sr_{3}SiO_{5}:Eu$ yellow phosphor by sol-gel technique. Based on the blue emitting diodes as primary light source, white light emitting diodes have been manufactured using the $Sr_{3}SiO_{5}:Eu$ yellow phosphor as the luminescent material. Luminescent efficiency of yellow phosphor as well as that of blue LED is very important factor to enhance the luminescent efficiency of white LED. In order to improve the luminescent efficiency, we have synthesized the $Sr_{3}SiO_{5}:Eu$ phosphor by sol-gel technique. To research optimum condition of gelation reaction, the ratio of $H_{2}O$ to TEOS was fixed as 60:1. When the drying temperature was at $100^{\circ}C$, emission intensity was better than at $70^{\circ}C$. The critical $Eu^{2+}$ concentration was estimated to be about 0.05 mol and sintering temperature at $1300^{\circ}C$ was indicated best emission intensity.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.103-108
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• 2003

A method to determine chromium(III) ion in aqueous solution by chemiluminescence method using a lucigenin entrapped silica sol-gel film has been studied. An optical probe for chromium(III) ion has been prepared by entrapping lucigenin into silica sol-gel film coated on a glass support by dip coating. The chromium(III) optical sensor is based on the catalytic effect of chromium(IIII) ion on the reaction between lucigenin and hydrogen peroxide in basic solutions. The effects of Nafion, DMF and Triton X-100 were investigated to find the optimum condition to minimize cracking and leaching from the probe. The effects of pH and concentrations of lucigenin and hydrogen peroxide on the chemiluminescence intensity were investigated. The chemiluminescence intensity was increased linearly with increasing chromium(III) concentration from $2.5{\times}10^{-4}$M to $8.0{\times}10^{-7}$M and the detection limit was $4.0{\times}10^{-7}$M.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.04a
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• pp.155-159
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• 2003

The preparation and luminescence characterization of yttrium oxide doped with trivalent europium phosphors by sol-gel method have been investigated. Aqueous metal nitrate solution was mixed with EDTA which was chosen by the most suitable material of sol-gel formation one of appled various chelating agents. we noticed that the samples when are heated with EDTA at a temperature of $100^{\circ}C$ for 1hrs, produced brownish and crisp powders due to condensation reaction on decomposition, dehydration and formation of sol-gel. Hence, when the powder pre-heated was then heated at $1200^{\circ}C$ for 3hrs in atmosphere, the luminescence characterization of resultant $Y_{2}O_{3}:Eu^{3+}$ phosphor was enhanced upto maximum 30% significantly than conventional method through increasing porous region and decreasing particle sizes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.04a
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• pp.151-154
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• 2003

The synthesis and luminescent properties of trivalent europium activated gadolinium oxide red phosphors by sol-gel process have been investigated. Aqueous metal nitrate solution was mixed with EDTA which was chosen by the most suitable material of sol-gel formation as chelating agents. We noticed that the samples when are heated with EDTA at a temperature of $100^{\circ}C$ for lhrs, produced brownish and crisp powders due to condensation reaction on decomposition, dehydration and formation of sol-gel. Hence, when the powder pre-heated at about $100^{\circ}C$ was then heated at $1200^{\circ}C$ for 3hrs in atmosphere, the luminescence properties of resultant $Gd_{2}O_{3}:Eu^{3+}$ phosphor was measured by SEM, FT-IT and brightness intensity was shown 20% higher than those prepared by conventional method and by other chelating agent.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.804-812
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• 1994

Stable PZT coating sol was prepared using chelating agent, ethylacetoacetate(EAcAc) by sol-gel processing under ambient atmosphere. Through FT-IR spectrum analysis on solution of each reaction step, formation of metal complex was confirmed and prepared PZT sol was stable over several months. Through TG-DTA, XRD, FT-IR spetrum analysis of PZT gel powder, it was understood that the addition of EAcAc could reduce the transition temperature to ferroelectric phase, due to the increased homogeneity by matching the hydrolysis and condensation rates by chelation. Single perovskite phase was obtained by the heat-treatment at 54$0^{\circ}C$ for 30 min. The film was coated on ITO-coated glass substrate by dip coating method. After heat-treatment, PZT thin film had thickness in the range of 20~130 nm. The maximum dielectric constant of its thin film at room temperature and 1 kHz was 128.

• Journal of the Korean Ceramic Society
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• v.36 no.9
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• pp.893-900
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• 1999

Silica films were prepared on Si single crystal substrates by sol-gel process using TEOS as starting materials. Films were fabricated by a spin coating technique. Sol solutions were prepared by varying the compositions of CH3OH, H2O and DMF with fixed molar ratio of TEOS=1, HCl=0.05(mol). Wetting behavior viscosity of solutions gelation time thickness of films and cracking behavior were investigated with the various solution compositions. Wetting behaviors of solutions depended on the solution compositions mixing method and mixing rate. The optimum composition of sol was TEOS : DMF ; CH3OH: H2O :HCl=1:2:4:4:0.05(mol) and the mixing rate of solution was optimized at 1 ml/min. Viscosity of solutions were controlled by choosing a reaction time(elapsed time after mixing) at a room temperature so that we could get up to 800nm thick film The surface roughness was getting poor when thickness of films was thicker than 500nm. Thickness of coated films were increased with decreasing amount of CH3OH. The best surface roughness was obtained at the content of CH3OH 4 mol. The shortest gelation time was obtained with the content of CH3OH 8 mol. Crack-free filkms were fabricated when sintered at 500$^{\circ}C$ for 1 hr with heating rate of 0.6$^{\circ}C$/min.