• Title/Summary/Keyword: Steric stabilization

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Preparation of Kerosine-Based Magnetic Ferrofluid by Steric Stabilizaton (Steric Stabilization에 의한 석유분산매 자성유체의 제조)

  • 신학기;장현명;김태옥
    • Journal of the Korean Ceramic Society
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    • v.27 no.5
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    • pp.684-692
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    • 1990
  • Ultrafine magnetite powder for the ferromagnetic fluid was prepared by an addition of alkaline solution to the solution containing Fe2+ and Fe3+ ions at 6$0^{\circ}C$. The optimum condition of the magnetite synthesis was delineated by examining such various physico-chemical properties as Fe2+/Fe+3 ratio in the powder, phase characteristics, MHC and $\sigma$max. A new scheme for the steric stabilization of colloidal dispersion was proposed using the concept of the buffer group action for the increased interfacial density of the stabilizing moieties at colloid particle/dispersion medium interface. The proposed concept was successfully applied to the preparation of the kinetically stable kerosinebased ferrofluid using Tween and Span as dispersants. In the dispersion of magnetite particles in a kerosine, Tween(polyoxyethylene sorbitan oleate) acts as a primary stabilizer which provides an anchor group, whereas Span(sorbitan oleate) can be classified as a secondary stabilizer which adsorbs on the surface of magnetite particle through the action of the buffer group. Dispersion studies using various quantities of Tween and Span supported the concept of the buffer group action for increased dispersion characteristics of the kerosine based ferromagnetic fluid.

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Rheological Behavior of Coal-Fly-Ash and Clay Slip (석탄회-점토계 슬립의 유동학적 거동)

  • 이기강;박천주;김유택;김석범;김정환
    • Journal of the Korean Ceramic Society
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    • v.35 no.2
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    • pp.180-184
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    • 1998
  • It was examined that the rheological behaviors of fly ash 70wt%-clay 30wt% slip in which nonplastic fly ash was a major component. We have systematically investigated the effects of deflocculant(Tetrasodium pyrophosphate ; Na4P2O7 nH2O Sodium silicate; Na2SiO3) and coagulant(CaSO4) on the rheological behavior of ash-clay slip. Ash-clay slip have been characterized on the basis of the time dependent rheology which was done out by the gel-curve test. Dispersion mechanism of ash-clay slip is the steric stabilization by the Na2SiO3 coating of cenospheres surface. Coagulated slip seems to have the new network structure and shows the gellation behaviors which makes it possible to direct coagulated casting(DCC).

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Effects of Synthetic Temperature and Suspension Stability of CeO2 Abrasive on CMP Characteristics (CeO2 연마입자의 합성온도와 수계안정성이 CMP 특성에 미치는 영향)

  • 임건자;김태은;이종호;김주선;이해원;현상훈
    • Journal of the Korean Ceramic Society
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    • v.40 no.2
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    • pp.167-171
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    • 2003
  • CMP(Chemical Mechanical Planarization) slurry for STI process is made by mechanically synthesized$CeO_2$as abrasive. The abrasive can be stabilized by electrostatic or steric stabilization in aqueous slurry and steric stabilization is more effective for long-term stability. Blanket-type$SiO_2$and $Si_3N_4$ wafers are polished with CMP slurry containing$CeO_2$synthesized in 50$0^{\circ}C$ or $700^{\circ}C$. Removal rate and surface uniformity of$SiO_2$and$Si_3N_4$wafer and selectivity are influenced by synthetic condition of abrasive, suspension stability and pH of slurries.

Improvement of Dispersion Stability of Ink-jet Ink for Polyester Fiber (폴리에스터용 잉크젯 잉크의 분산안정성 개선에 관한 연구)

  • 최재홍;지병철;서인석
    • Textile Coloration and Finishing
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    • v.15 no.5
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    • pp.321-326
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    • 2003
  • In order for disperse dye based ink to be fitted with the critical requirements of ink jet printing, this study was undertaken to investigate the effects of 6 different dispersants on the milling efficiency of insoluble dye particles and dispersion stability of the final ink. It was found that a polystyrene dispersant with high molecular weight exerted relatively better dispersion stability which may be associated with its steric stabilization effect in the ink solution.

The Steric Repulsion Properties of Polyethylene Oxide

  • Jeon, Sang Il;Joseph D. Andrade
    • Bulletin of the Korean Chemical Society
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    • v.13 no.3
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    • pp.245-248
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    • 1992
  • Polyethylene oxide (PEO) surfaces are recognized as having an effective steric stabilization character. A theoretical scaling analysis involves the osmotic and elastic coefficients of the polymer as a function of molecular weight, in a good solvent. The calculated results show that PEO in water may exhibit the greatest flexibility among water soluble polymers, probably due to its lowest elastic contribution.

Effects of Polymer Adsorption on Stabilities and CMP Performance of Ceria Abrasive Particles

  • Shimono Norifumi;Kawaguchi Masami;Koyama Naoyuki
    • Transactions on Electrical and Electronic Materials
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    • v.7 no.3
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    • pp.112-117
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    • 2006
  • In this paper we present that the effects of polymer adsorption on stabilities and CMP performance of ceria abrasive particles. Characterization of ceria abrasive particles in the presence of poly(vinyl pyrrolidone) (PVP) was performed by the measurements of adsorbed amounts of PVP, average sizes, and the back scattering intensities of the ceria abrasive particles as functions of PVP molecular weight and PVP concentration. The ceria abrasive particles in the presence of PVP were used to polish $SiO_2\;and\;Si_3N_4$ films deposited on Si wafers in order to understand the effect of PVP adsorption on chemical mechanical polishing (CMP) performance, together with ceria abrasive particles without PVP. Adsorption of PVP on the ceria abrasive particles enhanced the stability of ceria abrasive particles due to steric stabilization of the thick adsorbed layer of PVP. Removal rates of the deposited $SiO_2\;and\;Si_3N_4$ films by the ceria abrasive particles in the presence of PVP were much lower than those in the absence of PVP and their magnitudes were decreased with an increase in the concentration of free PVP chains in the dispersion media. This suggests that the CMP performance in the presence of PVP could be mainly controlled by the hydrodynamic interactions between the adsorbed PVP chains and the free ones. Moreover, the molecular weight dependence of PVP on the removal rates of the deposited films was hardly observed. On the other hand, high removal rate selectivity between the deposited films in the presence of PVP was not observed.

A Study on Fly Ash Substituted Slips and Consolidated bodies (석탄회 대체 슬립 및 고형화 소지에 관한 연구)

  • 김유택;박천주;김정환;이기강
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 1997.10a
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    • pp.181-186
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    • 1997
  • 석탄회의 재활용율을 높이고자 비가소성 원료인 석탄회를 첨가한 슬립 및 고형화 소지의 유동학적 고찰을 하였고, 이들을 이용하여 주입성형 후 소성한 시편의 물성들을 측정하였다. 석탄회가 50wt.%이상 대체된 슬립의 경우 해교 기구는 점토내 입자의 정전기적 반발력 보다는 석탄회에 포함된 cenosphere 입자표면의 물유리 흡착에 의한 steric stabilization에 의한 것으로 판단되었다. 응집된 슬립은 전형적인 thixotrophy 현상을 나타내는 반면 분산후 재응집된 슬립은 점도가 계속 증가하는 겔화현상을 나타내어 망목구조를 갖는 성형체를 제조할 수 있었다. 석탄회 대체율 50wt.%의 소성체에서 가장 우수한 물성치를 얻을 수 있었으며, 대체율 70wt.%까지의 주입성형이 가능하였다.

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음이온형 수분산성 공중합 폴리에스테르의 합성 및 응용 연구(II)

  • 엄성일;고석원
    • Proceedings of the Korean Fiber Society Conference
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    • 1994.10a
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    • pp.137-138
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    • 1994
  • Anionic water dispersible copolyesters were synthesized and characterized. Viscosity of the copolyester is lower than that of routine acrylic water dispersible polymers. Adhesive force of the copolyester was much higher than that of water dispersible acrylic polymers. Particle size of the copolyesters in water decreased with the increase of DMS or DEG feed ratio. With the conclusive study of the data of particle size and potential, it was found that the dispersion stability of copolyesters in water increased with the increase of DMS or DEG feed ratio. Judging from the results of potential and particle size of copolyesters, there seems to be competition between two dispersion stability factors, i.e. electrostatic stabilization and steric stabilization and as a result, morphological change of particles occurrs. Tg decreased with the increase of DEG molar feed ratio or oil contents.

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Biodistribution and Hemolysis Study of Terplex Gene Delivery System in Mice

  • Oh, Eun-Jung;Shim, Jin-young;Kim, Jin-Seok
    • Macromolecular Research
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    • v.11 no.1
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    • pp.19-24
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    • 2003
  • Polymeric gene delivery system attracts profound attention as it shows less toxicity, versatility, and reasonable gene expression efficiency. Terplex system, a synthetic biopolymeric gene delivery system consisting of stearyl poly-L-lysine (stearyl-PLL) and low density lipoprotein (LDL) was evaluated for its body distribution of gene expression of exogenously administered pDNA after tail-vein injection in mice. Kidney and spleen are two major organs with highest gene expression, whereas liver and heart showed marginal gene expression among the organs examined. Hemolytic effect of the terplex system was evaluated using human red blood cells, where terplex system did not cause significant hemolysis at the concentrations above the experimental ranges, although unmodified PLL or stearyl-PLL without LDL did. Serum stability of terplex system against enzymatic degradation was also significantly enhanced, presumably due to the steric stabilization from the polymers. Based on these findings and along with its high in vitro transfection efficiency, terplex system could serve as a safe and efficient polymeric gene delivery system with many applications for the in vivo gene therapy.

Investigation on Flocculi-floc Interaction and Flocculation in Extracellular Polymeric Substances, Ionic Species and Clay-containing Suspension (생체고분자물질 농도와 이온강도에 따른 점토입자 현탁액의 응집핵-응집체 이군집 응집 특성 연구)

  • Kim, Jae In;Lee, Byung Joon
    • Journal of Korean Society on Water Environment
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    • v.36 no.3
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    • pp.185-193
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    • 2020
  • Bimodal flocculation describes the aggregation and breakage processes of the flocculi (or primary particles) and the flocs in the water environment. Bimodal flocculation causes bimodal size distribution with the two separate peaks of the flocculi and the flocs. Extracellular polymeric substances and ionic species common in the water environment increase the occurrence of bimodal flocculation and flocculi-floc size distribution, under the flocculation mechanisms of electrostatic attraction and polymeric bridging. This study investigated bimodal flocculation and flocculi-floc size distribution, with respect to the extracellular polymeric substance concentration and ionic strength in the kaolinite-containing suspension. The batch flocculation tests comprising 0.12 g/L of kaolinite showed that the highest flocculation potential occurred at the lowest xanthan gum (as extracellular polymeric substances) concentration, under all the ionic strengths of 0.001, 0.01, and 0.1 M NaCl. Also, it was important to note that the higher ionic strength resulted in the higher flocculation potential, at all the xanthan gum concentrations. The bimodal flocculation and flocculi-floc size distribution became apparent in the experimental conditions, which had low and intermediate flocculation potential. Besides the polymeric bridging flocculation, steric stabilization increased the flocculi mass fraction against the floc mass fraction, thereby developing the bimodal size distribution.