• 한국세라믹학회지
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• 제45권10호
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• pp.644-650
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• 2008

It has been proposed that the Cao-$SiO_2$ binary system can be good basic composition of bioactive glasses and glass-ceramics. In the present study, various kinds of Cao-$SiO_2$ gels were prepared by sol-gel method in order to control the microstructure which are related to their dissolution rate, induction period of apatite formation in body environment. Characterization of the gels were done by wet chemical analysis, SEM observation, FT-IR spectroscopy and XRD. The gelation time decreased with CaO content. However, the volume of all the dried gel decreased to 50% of the wet gels irrespective of increasement of CaO content. All the Cao-$SiO_2$ gels were amorphous and contained a large amount of silanol groups on their surfaces after heat treatment up to $800^{\circ}C$. The interconnected structure of the gel changed to agglomerated spherical powders when Ca content exceed to 20 mol%. Most of the Cao-$SiO_2$ gel showed amorphous when heat-treated up to $900^{\circ}C$. However, quartz and cristobalite was produced when heat-treated at $1000^{\circ}C$ and resultant microstructure of the gel contained microporous structure.

• 대한화학회지
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• 제38권8호
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• pp.562-569
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• 1994

$ C_{18}$ 및 Phenyl 컬럼에서 메탄올-물 및 아세토니트릴-물 혼합액을 이동상으로 하여 21종의 페놀일치환체들의 머무름을 조사하여 치환기가 머무름에 미치는 영향을 알아보았다. 아미노페놀을 제외한 모든 시료의 머무름은 Phenyl 컬럼보다 $ C_{18}$컬럼에서 더 컸으며, 두 이동상에 대해서는 물의 부피퍼센트가 같을때 메탄올계에서 더 컸다. 일반적으로 일치환 페놀류의 파라 이성질체는 메타 이성질체보다 빨리 용리되었고, 오르토와 메타 이성질체 사이에서는 용리순서가 치환기의 극성에 따라 다르게 나타났다. 페놀 일치환체들의 머무름은 시료와 미반응된 실란올과의 상호작용의 영향을 받는대 이러한 미반응된 실란올의 영향은 치환기의 hydrogen bonding acceptor basicity(${\beta}$)가 클수록 크게 나타났고 Phenyl 컬럼보다 $ C_{18}$ 컬럼에서 이들의 영향이 크게 나타났다. 시료의 van der Waals volume(VWV)과 ${\beta}$값을 함께 고려한 파라미터 (1.01VWV/100-1.84${\beta}$)와 시료의 머무름(log k')과는 좋은 직선관계가 있다. 따라서 $ C_{18}$ 및 Phenyl 컬럼에서 페놀 일치환체들의 머무름은 시료의 (1.01VWV/100-1.84${\beta}$)값으로 쉽게 예측할 수 있음을 알았다.

• Elastomers and Composites
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• 제55권3호
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• pp.215-221
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• 2020

Silica/SBR (styrene-butadiene rubber) compounds are the primary constituents of tire treads. Furthermore, the excellent dynamic viscoelastic properties of silica lead to good fuel efficiencies. However, the silanol group on the surface of silica does not mix well with non-polar rubber because of its polarity. This incompatibility causes aggregation due to the occurrence of hydrogen bonding between the hydroxyl groups, thereby reducing the dispersibility of silica. Recently, the wet master batch (WMB) process has been applied to overcome these disadvantages, and research on silica dispersants that can be used in the WMB process has been increasing. In this study, we prepared silica/SBR compounds by using three types of eco-friendly cellulose-based dispersants in the WMB process, namely: cellulose-, sodium carboxymethyl cellulose, and nanocellulose-based dispersants. Subsequently, we compared the vulcanization characteristics, viscoelastic properties, and mechanical properties of the compounds. The silica dispersibility in the rubber compounds was improved with the addition of the nano-cellulose dispersant, resulting in the enhancement of the workability, hardness, tensile strength, and wear resistance of the SBR compound.

• 한국분말재료학회지
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• 제9권5호
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• pp.365-369
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• 2002

Silica hydrogel was synthesized by the reaction of liquid sodium silicate with sulfuric acid. The condensation polymerization of the synthesized hydrogel was carried out via an aging process under the acidic or alkaline conditions. Nano porous silica with the pore size below 3 nm and surface area of $715m^2/g$, was obtained by the above processes in acidic ranges(pH : 3~5). The pore size and surface area of the silica varied with pH, and in alkaline ranges(pH : 8~10), those were 21 nm and $300m^2/g$ respectively. The characteristics of the silica varied with the thermal treatment which caused the change of surface area, pore volume and pore diameter.

• Macromolecular Research
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• 제16권5호
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• pp.399-403
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• 2008

Monodisperse, micron-sized, hybrid particles having a core-shell structure were prepared by coating the surface of poly(methyl methacrylate)(PMMA) microspheres with silica and by copolymerizing acrylamide (AAm) to supply the hydrogen bonding effect by means of the amide groups. Tetraethoxysilane (TEOS) was then slowly dropped onto the medium under certain conditions. Because of the hydrogen bonding between the amide of the PMMA particles and the hydroxyl group of the hydrolyzed silanol, a silica shell was generated on the PMMA core particles. The morphology of the hybrid particles was investigated with transmission (TEM) and scanning (SEM) electron microscopy as a function of the medium conditions and the amount of TEOS. Improved thermal properties were observed by TGA analysis.

• 대한화장품학회지
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• 제13권1호
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• pp.15-28
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• 1987

Silica spheres were prepared by interfacial reaction method. Factors in-fluencing to the mean particle size and specific surface area of silica spheres were investigated. The experiment about the surface modification of silica spheres was carried out. It was observed that silica spheres have characteristics of the spherical shape with the vacancy in the inner side, high surface area, and reaction tendency by many silanol group. The mean particle size of silica spheres is dependent on the surfactant concentration and W/O ratio. The specific surface area is influenced by SiO2/Na2O mole ratio in sodium silicate. Silica spheres coated with titanium dioxide or zirconium dioxide improve the UV protection effect. Titanate and silane coupling agent make chemical bond with silica surface and improve the organophile and the dispersibility of silica spheres.

• Bulletin of the Korean Chemical Society
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• 제18권2호
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• pp.203-208
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• 1997

A series of MgO-SiO2 catalysts were prepared by coprecipitation from the mixed solution of magnesium chloride and sodium silicate. Some of the sample were modified with 1 N H2SO4 and used as modified catalysts. The addition of MgO to SiO2 caused the increase of acidity and the shift of O-H and Si-O stretching bands of the silanol group to a lower frequency in proportion to the MgO content. The acid structure of MgO-SiO2 agreed with that proposed by Tanabe et al.. Catalytic activity for 2-propanol dehydration increased in relation to the increase of acidity and band shift to a lower frequency.

• Korean Chemical Engineering Research
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• 제49권4호
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• pp.460-464
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• 2011

Poly(ether-block-amide)(PEBA, $PEBAX^{TM}$)는 열가소성 탄성체(thermoplastic elastomer, TCU)로서 hard-rigid amide block과 soft-flexible ether block으로 구성되어 있으며, 분자량과 두 block간의 구성비에 따라 여러 종류가 있다. $PEBAX^{TM}$는 분리막소재로 이용할 경우, $PEBAX^{TM}$의 hard amide block은 우수한 기계적 특성과 선택도를, 그리고 soft ether block은 높은 투과도를 제공할 수 있다. 따라서 본 연구에서는 2종류의 $PEBAX^{TM}$를 사용하여 기체분리막을 제조하고, 종류에 따른 이산화탄소와 메탄의 투과특성 변화를 연구하였다. 또한 순수 $PEBAX^{TM}$ 분리막의 투과특성을 향상시키기 위해 무기전구체로서 TEOS(tetraethoxysilane)를 사용하여 $PEBAX^{TM}$/TEOS 하이브리드막을 제조하고, 그 투과특성을 순수 $PEBAX^{TM}$ 분리막의 결과와 비교하였다. 순수 $PEBAX^{TM}$-1657과 $PEBAX^{TM}$-2533 분리막의 투과도 측정 결과, ether block의 비율이 상대적으로 높은 $PEBAX^{TM}$-2533 분리막의 투과도 계수가 보다 높은 투과도 계수값을 가졌다. 이는 $PEBAX^{TM}$-2533의 경우, 상대적으로 높은 ether block 함량 때문에 고분자 사슬의 유연성이 보다 크기 때문으로 볼 수 있다. $PEBAX^{TM}$/TEOS 하이브리드 분리막의 투과특성을 순수 $PEBAX^{TM}$ 분리막의 결과와 비교할 때, 하이브리드 분리막의 기체 투과도 계수가 보다 높음을 알 수 있다. 이는 TEOS의 축합반응으로 생성된 silica domain에 의해 결정성이 감소하고 또한 이산화탄소와 silanol group과의 친화도(affinity) 증가에 따른 용해도가 증가하기 때문으로 볼 수 있다. 하이브리드 분리막의 투과도 계수 증가에도 불구하고 이상분리인자는 거의 비슷하거나 약간 감소하였음을 알 수 있다. 이는 이산화탄소와 silanol group의 친화도 증가로 인한 용해선택도의 증가에 기인한 것으로 볼 수 있다.

• 접착 및 계면
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• 제7권4호
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• pp.39-44
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• 2006

A new kind of silicone-epoxy composite is reported in this research. The silicone-epoxy resin was synthesized by the hydrosilylation of tetramethycyclotetrasiloxane and 4-vinyl-1-cyclohexene 1,2-epoxy with a high reaction yield. It was found that the obtained silicone-epoxy resin shows a high reactive activity to the aluminum complex-silanol catalyst. The resin could be cured under the catalysis of $(Al(acac)_3/Ph_2Si(OH)_2$ at a concentration below 0.1 wt% to give a hard cured resin showing excellent optical clarity, UV resistance and thermal stability. It was also found that the Si-H groups facilitated the curing reaction and the silicone-epoxy resin bearing Si-H group could be cured effectively even if $Ph_2Si(OH)_2h$ was absent. Moreover, the UV resistance and thermal stability were improved significantly by the introduction of Si-H groups. This is possibly due to the reductive property of Si-H groups which can annihilate radical and peroxide effectively. This kind of silicone-containing epoxy composite might have very promising applications as optical resin, optical adhesive and encapsulation materials for electronic devices.

• 한국세라믹학회지
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• 제45권2호
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• pp.119-125
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• 2008

The FAS(Fluoroalkylsilane)/Nafion inorganic-organic composite electrolyte membrane was successfully fabricated through sol-gel method. The FAS having hydrophobic functional group and silanol ligands is impregnated in $Nafion^{(R)}$ membrane to reduce methanol crossover. The prepared FAS/Nafion inorganic-organic composite electrolyte membrane consist of the hydrophobic FAS-derived silicate nano-particles and $Nafion^{(R)}$ matrix showed decrease of methanol crossover and reduction of humidity dependence without large sacrifice of proton conductivity. The microstructural analysis of the composite membranes was performed using FESEM and FTIR. And the effect of the incorporation of the hydrophobic FAS-derived silicate nano-particles into $Nafion^{(R)}$ membrane was investigated via solvent uptake, membrane expansion rate, humidity dependency of proton conductivity and contact angle measurement.