• Title/Summary/Keyword: silica

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Synthesis of Flake Type Micro Hollow Silica Using Mg(OH)2 Inorganic Template

  • Lee, Ji-Seon;Noh, Kyeong-Jae;Moon, Seong-Cheol;Lee, Young-Chul;Lee, Seong-Eui
    • Journal of the Korean Ceramic Society
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    • v.54 no.3
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    • pp.222-227
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    • 2017
  • Flake-type micro hollow silica was synthesized by precipitation method using an $Mg(OH)_2$ inorganic template and sodium silicate and ammonium sulfate as the silica precursors. We investigated the effects of the silica precursor concentration on the shape, shell thickness, and surface of the hollow silica. When the concentration of the silica precursor was 0.5 M, the hollow silica had a smooth and translucent thin shell, but the shell was broken. On the other hand, the shell thickness of the hollow silica changed in the range of 12 nm to 18 nm with the increase of the precursor concentration from 0.7 M to 1.1 M. Simultaneously, unintended spherical silica satellites were created on the shell surface. The number of satellites and the size rose according to the increased concentration of silica precursor. The reason for the formation of spherical silica satellites is that the $NH_4OH$ nucleus generated in the synthesis of hollow silica acted as another silica reaction site.

Induction of Functional Changes of Dendritic Cells by Silica Nanoparticles

  • Kang, Kyeong-Ah;Lim, Jong-Seok
    • IMMUNE NETWORK
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    • v.12 no.3
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    • pp.104-112
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    • 2012
  • Silica is one of the most abundant compounds found in nature. Immoderate exposure to crystalline silica has been linked to pulmonary disease and crystalline silica has been classified as a Group I carcinogen. Ultrafine (diameter <100 nm) silica particles may have different toxicological properties compared to larger particles. We evaluated the effect of ultrafine silica nanoparticles on mouse bone marrow-derived dendritic cells (BMDC) and murine dendritic cell line, DC2.4. The exposure of dendritic cells (DCs) to ultrafine silica nanoparticles showed a decrease in cell viability and an induction of cell death in size- and concentration-dependent manners. In addition, in order to examine the phenotypic changes of DCs following co-culture with silica nanoparticles, we added each sized-silica nanoparticle along with GM-CSF and IL-4 during and after DC differentiation. Expression of CD11c, a typical DC marker, and multiple surface molecules such as CD54, CD80, CD86, MHC class II, was changed by silica nanoparticles in a size-dependent manner. We also found that silica nanoparticles affect inflammatory response in DCs in vitro and in vivo. Finally, we found that p38 and NF-${\kappa}B$ activation may be critical for the inflammatory response by silica nanoparticles. Our data demonstrate that ultrafine silica nanoparticles have cytotoxic effects on dendritic cells and immune modulation effects in vitro and in vivo.

Fabrication of Nearly Monodispersed Silica Nanoparticles by Using Poly(1-vinyl-2-pyrrolidinone) and Their Application to the Preparation of Nanocomposites

  • Chung, You-Sun;Jeon, Mi-Young;Kim, Chang-Keun
    • Macromolecular Research
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    • v.17 no.1
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    • pp.37-43
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    • 2009
  • To fabricate dental nanocomposites containing finely dispersed silica nanoparticles, nearly monodispersed silica nanoparticles smaller than 25 nm were synthesized without forming any aggregates via a modified sol-gel process. Since silica nanoparticles synthesized by the Stober method formed aggregates when the particle size is smaller than 25 nm, the synthetic method was modified by changing the reaction temperature and adding poly(1-vinyl-2-pyrrolidinone) (PVP) to the reaction mixture. The size of the formed silica nanoparticles was reduced by increasing the reaction temperature or adding PVP. Furthermore, the formation of aggregates with primary silica nanoparticles smaller than 25 nm was prevented by increasing the amount of PVP added to the reaction mixture. To enhance the dispersion of the silica particles in an organic matrix, the synthesized silica nanoparticles were treated with 3-methacryloxypropyltrimethoxysilane ($\gamma$-MPS). A dental nanocomposite containing finely dispersed silica nanoparticles could be produced by using the surface-treated silica nanoparticles.

Properties of EMNC according to Addition Contents Variation for Nanosilica (1) -For Thermal Properties (나노실리카 충진함량 변화에 따른 EMNC의 특성연구 (1) -열적특성 중심으로-)

  • Choi, Woon-Shik;Park, Jae-Jun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.25 no.10
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    • pp.798-804
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    • 2012
  • This paper focuses on thermal properties of a newly prepared composite material by nano-silica and micro-silica mixture. Nano-silica and micro-silica mixture composites were made by dispersing surface treated nano-silica(average radius: 10 nm) and micro-size silica in epoxy resin. To investigate the effects of nano-silica and micro-size silica mixture(ENMC), the glass transition temperature (Tg), coefficients of thermal expansion(CTE) and elastic modulus of DMA properties by DSC, TMA and DMA devices were measured for the ENMC according to increase nano-silica addition contents and EMC. All properties of the neat epoxy were improved by the addition of micro-silica, which was improved much further by the addition of surface treated nano-silica to the EMC system.

Study on the Change of Physical Properties with Silica Contents in Solution Styrene-Butadiene Rubber (SSBR)/Silica Composites

  • Kim, Tae Yeop;Won, Sung Yeon;Kang, Shin Hye;Cho, Ur Ryong
    • Elastomers and Composites
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    • v.52 no.1
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    • pp.17-21
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    • 2017
  • The optimum mixing conditions of silica and silane containing rubber composites were evaluated by investigating the properties of rubber composites prepared with a silica composition of 10, 20, 40, 60, and 80 g, respectively. The crosslinking rate decreased with increasing silica content, with he promoters being adsorbed on the silica surface with in the rubber composite. As a result, the increase in crosslinking time resulted in the destruction of the silica structure. The increase of the bound rubber content due to the destruction of the silica structure inhibited the chain motion of the polymer molecules and reduced the cohesion of the silica itself. Finally, the increase of silica content showed the increase of hardness, tensile strength, and storage modulus of rubber composites.

Enhancement of Scratch Resistance of Polycarbonate by the Addition of Mineral Silica (실리카 첨가에 의한 폴리카보네이트 수지의 니스크래치 특성 개선)

  • Lee, Byung-Ick;Lim, Gyun-Taek;Lee, Moo-Sung
    • Textile Science and Engineering
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    • v.48 no.3
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    • pp.142-149
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    • 2011
  • Polycarbonate (PC)/mineral silica composites were prepared by melt-mixing to improve PC's surface characteristics. The silica's surface was modified using a silane coupling agent with amine functional moiety prior to blending. The effects of silica on the PC's morphology, dynamic mechanical properties, molecular weight, and pencil hardness were investigated. Although SEM showed that silane treatment promoted interfacial adhesion between the PC and the silica, the storage modulus of the PC/silica composites increases with increasing silica content irrespective of silane treatment. Silica addition decreased the molecular weight (MW), and thus the melt viscosity of PC in the composites. The reduction was slightly greater at higher silica contents and when silane-treated silica was added. Despite the detrimental effects of silica on the MW, the pencil hardness of the PC increased to F grade when silane-treated silica of 40 phr was added possibly due to the increased modulus and interfacial adhesion.

Crystallization and Melting Behavior of Silica Nanoparticles and Poly(ethylene 2,6-naphthalate) Hybrid Nanocomposites

  • Kim Jun-Young;Kim Seong-Hun;Kang Seong-Wook;Chang Jin-Hae;Ahn Seon-Hoon
    • Macromolecular Research
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    • v.14 no.2
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    • pp.146-154
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    • 2006
  • Organic and inorganic hybrid nanocomposites based on poly(ethylene 2,6-naphthalate) (PEN) and silica nanoparticles were prepared by a melt blending process. In particular, polymer nanocomposites consisting mostly of cheap conventional polyesters with very small quantities of inorganic nanoparticles are of great interest from an industrial perspective. The crystallization behavior of PEN/silica hybrid nanocomposites depended significantly on silica content and crystallization temperature. The activation energy of crystallization for PEN/silica hybrid nanocomposites was decreased by incorporating a small quantity of silica nanoparticles. Double melting behavior was observed in PEN/silica hybrid nanocomposites, and the equilibrium melting temperature decreased with increasing silica content. The fold surface free energy of PEN/silica hybrid nanocomposites decreased with increasing silica content. The work of chain folding (q) for PEN was estimated as $7.28{\times}10^{-20}J$ per molecular chain fold, while the q values for the PEN/silica 0.9 hybrid nanocomposite was $3.71{\times}10^{-20}J$, implying that the incorporation of silica nanoparticles lowers the work required to fold the polymer chains.

Optimization of Cure System for the ESBR Silica WMB and BR Silica DMB Blend Compounds

  • Yu, Eunho;Kim, Woong;Ryu, Gyeongchan;Ahn, Byungkyu;Mun, Hyunsung;Hwang, Kiwon;Kim, Donghyuk;Kim, Wonho
    • Elastomers and Composites
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    • v.54 no.2
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    • pp.97-104
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    • 2019
  • Emulsion styrene-butadiene rubber silica wet masterbatch (ESBR silica WMB) technology was studied to develop highly filled and highly dispersed silica compounds, involving the preparation of a composite by co-coagulating the modified silica and the rubber latex in a liquid phase. Previous studies have shown that when manufacturing ESBR silica WMB/Butadiene silica dry masterbatch (BR silica DMB) blend compounds, preparing BR silica dry masterbatch and mixing it with ESBR silica WMB gave excellent results. However, WMB still has the problem of lower crosslink density due to residual surfactants. Therefore, in this study, tetrabenzylthiuram disulfide (TBzTD) was added instead of diphenyl guanidine (DPG) in the ESBR silica WMB/BR silica DMB blend compounds and sulfur/CBS contents were increased to evaluate their cure characteristics, crosslink densities, mechanical properties, and dynamic viscoelastic properties. TBzTD was found to be more effective in increasing the crosslink density and to produce superior properties compared to DPG. In addition, with increasing sulfur/CBS contents, mechanical properties and rolling resistance were enhanced due to high crosslink density, but the abrasion resistance was not significantly changed because of the toughness.

Correlation Research of Dispersion Factors on the Silica Sol Prepared from Fumed Silica (흄드실리카로부터 제조된 실리카졸의 분산인자 상관성 연구)

  • Park, Min-Gyeong;Kim, Hun;Lim, Hyung Mi;Choi, Jinsub;Kim, Dae Sung
    • Korean Journal of Materials Research
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    • v.26 no.3
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    • pp.136-142
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    • 2016
  • To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

Studies on the Chemical Treatment of Silica for Synthetic Rubber Reinforcement (II) -Silica Treatment by LBR-MDI- (합성(合成)고무 보강제(補强劑) Silica의 화학처리(化學處理)에 관(關)한 연구(硏究) (II) -MDI 처리(處理) Silica의 LBR처리(處理)-)

  • Jin, Je-Yong;Kim, Hong-Seon;Choi, Sei-Young
    • Elastomers and Composites
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    • v.30 no.3
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    • pp.207-217
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    • 1995
  • The reinforcement of Inorganic filler silica treated with LBR-MDI In SBR vulcanizates were Investigated. The inorganic filler silica treated with MDI on unmodified surface and that of silica treated by MDI was retreated with LBR. The charateristics of vulcanization, physical properties, surface properites and dynamic properties were investigated after mixing those silica with SBR and unmodified silica with SBR. Rheometric studies of the vulcanization showed that S-series has fast scorch $time(t_{10})$ and an optimum cure $time(t_{90})$ in the SBR compounds. And it was turned out that SBR vulcanizates compounded with LBR treated silica was better than any other componnds in hardness, tensile strenght, 100 300% modula and elongation. We could confirm that urea bonding is formed from IR spectrum. We concluded that L-series shows the best reinforcement effect in SBR vulcanizates.

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