• Title/Summary/Keyword: Colloidal suspensions

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Fractal Nature of Magnetic Colloidal Dispersion with Cobalt Iron Oxide and Metal Iron Particles

  • Yoon, Kwan Han;Lee, Young Sil
    • Korean Chemical Engineering Research
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    • v.60 no.1
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    • pp.125-131
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    • 2022
  • The microstructure of highly aggregated colloidal dispersions was investigated by probing the rheological behavior of magnetic suspensions. The dynamic moduli as functions of frequency and strain amplitude are shown to closely resemble that of colloidal gels indicating the formation of network structure. The two types of characteristic critical strain amplitudes, γc and γy, were characterized in terms of the changing microstructure. The amplitude of γc indicates the transition from linear to nonlinear viscoelasticity and depends only on particle volume fraction not magnetic interactions. The study of scaling behavior suggests that it is related to the breakage of interfloc, i.e., floc-floc structure. However, yielding strain, γy, was found to be independent of particle volume fraction as well as magnetic interaction. It relates to extensive deformation resulting in yielding behavior. The scaling of elastic constant, Ge, implies that this yielding behavior and hence γy is due to the breakage of long-range interfloc interactions. Also, the deformation of flocs due to increase strain was indicated from the investigation of the fractal nature.

Fundamentals of Particle Fouling in Membrane Processes

  • Bhattacharjee Subir;Hong Seungkwan
    • Korean Membrane Journal
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    • v.7 no.1
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    • pp.1-18
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    • 2005
  • The permeate flux decline due to membrane fouling can be addressed using a variety of theoretical stand-points. Judicious selection of an appropriate theory is a key toward successful prediction of the permeate flux. The essential criterion f3r such a decision appears to be a detailed characterization of the feed solution and membrane properties. Modem theories are capable of accurately predicting several properties of colloidal systems that are important in membrane separation processes from fundamental information pertaining to the particle size, charge, and solution ionic strength. Based on such information, it is relatively straight-forward to determine the properties of the concentrated colloidal dispersion in a polarized layer or the cake layer properties. Incorporation of such information in the framework of the standard theories of membrane filtration, namely, the convective diffusion equation coupled with an appropriate permeate transport model, can lead to reasonably accurate prediction of the permeate flux due to colloidal fouling. The schematic of the essential approach has been delineated in Figure 5. The modern approaches based on appropriate cell models appear to predict the permeate flux behavior in crossflow membrane filtration processes quite accurately without invoking novel theoretical descriptions of particle back transport mechanisms or depending on adjust-able parameters. Such agreements have been observed for a wide range of particle size ranging from small proteins like BSA (diameter ${\~}$6 nm) to latex suspensions (diameter ${\~}1\;{\mu}m$). There we, however, several areas that need further exploration. Some of these include: 1) A clear mechanistic description of the cake formation mechanisms that clearly identifies the disorder to order transition point in different colloidal systems. 2) Determining the structure of a cake layer based on the interparticle and hydrodynamic interactions instead of assuming a fixed geometrical structure on the basis of cell models. 3) Performing well controlled experiments where the cake deposition mechanism can be observed for small colloidal particles (< $1\;{\mu}m$). 4) A clear mechanistic description of the critical operating conditions (for instance, critical pressure) which can minimize the propensity of colloidal membrane fluting. 5) Developing theoretical approaches to account for polydisperse systems that can render the models capable of handing realistic feed solutions typically encountered in diverse applications of membrane filtration.

Non-equilibrium Monte Carlo Simulations for Critical Flux of Hard Sphere Suspensions in Crossflow Filtration

  • Kim, Albert S.
    • Proceedings of the Membrane Society of Korea Conference
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    • 2008.05a
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    • pp.33-47
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    • 2008
  • Non-equilibrium (irreversible) themodynamics is used to investigate colloidal back-diffusion during crossflow membrane filtration. The chemical potential is generalized as a superposition of equilibrium and irreversible contributions, originating from Brownian and shear-induced diffusion, respectively. As a result, an effective drag force is derived using the irreversible thermodynamics for a particle undergoing both Brownian and shear-induced diffusion in a sheared concentrated suspension. Using the drag force, a hydrodynamic force bias Monte Carlo method is developed for crossflow membrane filtration to determine the critical flux of hard sphere suspensions. Effects of shear rate and particle size on the critical flux are studied, and results show a good agreement with experimental observations reported in the literature.

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Electrorhelological Properties of Monodispersed Submicron-sized Hollow Polyaniline Adipate Suspension

  • Sung, Bo-Hyun;Choi, Ung-Su
    • KSTLE International Journal
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    • v.6 no.1
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    • pp.28-32
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    • 2005
  • The electrorheoloRical (ER) fluids are composed of a colloidal dispersion of polarizable particles in insulating oil, and it's the rheological property changes by the applied electric field. These changed are reversible and occur fast within a fewmilliseconds. The ER properties of the ER fluid such as increment of viscosity and yield stress come from the particle chain structure induced by electric fleld. When formulating the ER fluid for a speciflc application, some requirement must besatisfled, which are high yield stress under electric field, rapid response, and dispersion stability. While this characteristic makes valuable ER fluids in valious industrial applications, their lung term and quiescent application has been limited because ofproblems with particle sedimentation. In an effort to overcome sedimentation problem of ER fluids, the anhydrous ER materials of monodispersed hollow polyaniline (PANI) and adipate derivative respectively with submicron-sized suspension providing wide operating temperature range and other advantage were synthesized in a four-step procedure. The ER fluidswere characterized by FT-lR, TGA, DLS, SEM, and TEM. Stability of the suspensions was examined by an UV spectroscopy.The rheological and electrical properties of the suspension were investigated Couette-type rheometer with a high voltagegenerator, current density, and conductivity. And the behavior of ER suspensions was observed by a video camera attached toan optical microscope under 3kV/mm. The suspensions showed good ER properties, durability, and particle dispersion.

Adsorption of Colloidal Silica Particles on a Glass Substrate

  • Sim, Soo-Man
    • Journal of the Korean Ceramic Society
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    • v.39 no.11
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    • pp.1011-1016
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    • 2002
  • Colloidal particles of silica (100 nm in size) were electrostatically dispersed and adsorbed on a glass substrate coated with silica sol or alumina sol. Stability of the suspensions and microstructure of the adsorbed particle layers were discussed in terms of total potential energies between the particles and the substrate. Well-dispersed suspension resulted in a layer with densely packed and regularly arranged particles, whereas less stable suspension resulted in a porous layer with loosely packed and irregularly arranged particles. Despite repulsive interactions between the particles and the substrate coated with silica sol, the observed adsorption can be attributed to chemical bonds formed at the interface between the particle and silica sol. In contrast, the adsorption of the particles on the substrate coated with alumina sol formed a layer with strongly adhered and densely packed particles, due to large attractive interactions between the particles and alumina sol.

Material Dependence of Laser-induced Breakdown of Colloidal Particles in Water

  • Yun, Jong-Il
    • Journal of the Optical Society of Korea
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    • v.11 no.1
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    • pp.34-39
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    • 2007
  • Laser-induced breakdown of colloidal suspensions, such as polystyrene, $ZrO_2$, and $SiO_2$ particles in diameters of 100-400 nm in water is investigated by nanosecond flash-pumped Nd:YAG laser pulses operating at a wavelength ${\lambda}$= 532 nm. The breakdown threshold intensity is examined in terms of breakdown probability as a function of laser pulse energy. The threshold intensity for $SiO_2$ particles ($1.27{\times}10^{11}\;W/cm^2$) with a size of 100 nm is higher than those for polystyrene and $ZrO_2$ particles with the same size, namely $5.7{\times}10^{10}$ and $5.5{\times}10^{10}\;W/cm^2$, respectively. Results indicate that the absorption of five photons is required to induce ionization of $SiO_2$ particles, whereas the other particles necessitate four-photon absorption. These breakdown thresholds are compared with those measured by nanosecond pulses from a diode-pumped Nd:YAG laser having a different focusing geometry.

Migration in concentrated suspension of spherical particles dispersed in polymer solution

  • Kim, Chongyoup
    • Korea-Australia Rheology Journal
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    • v.13 no.1
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    • pp.19-27
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    • 2001
  • In this symposium paper, the migration and hydrodynamic diffusion of non-colloidal, spherical particles suspended in polymer solutions are considered under Poiseuille or torsional flows. The migration phenomena in polymer solutions are compared with those in Newtonian fluids and the effect of fluid elasticity is discussed. The experimental results on particle migration in dilute polymer solution reveal that even a slight change in the rheological property of the dispersing medium can induce drastic differences in flow behavior and migration of particles, especially in dilute and semi-concentrated suspensions.

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Effect of Colloidal Silica on Electredeposited Film from Copper sulfate Bath (황산구리 전해욕의 전착피막에 미치는 콜로이달실리카의 영향)

  • Lee, Sang-Baek;Kim, Byeong-Il;Yun, Jeong-Mo;Park, Jeong-Hyeon
    • Korean Journal of Materials Research
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    • v.11 no.5
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    • pp.413-418
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    • 2001
  • We investigated change of crystal structure, surface morphology and crystal orientation of the electrodeposited film from dispersed $SiO_2$ suspensions (colloidal silica) copper sulfate bath and arse corrosion potentials and physical specific properties. As addition of colloidal silica in copper electrolytic hath, the crystal Particles on filial was fined-down, made uniform and account of particles were increased. Hardness of copper electrodeposited film ascended about 15% and (111), (200) and (311) plane of X-ray diffraction patterns were almost swept away, so preferred orientation chanced from (111) to (110) plane. Also, corrosion potential of electrodeposited copper film was noble with colloidal silica addition.

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Fouling Behavior of Bentonite Colloidal Suspensions in Microfiltration (벤토나이트 현탁액에 의한 정밀여과 막의 오염특성)

  • Nam, Suk-Tae;Han, Myeong-Jin
    • Membrane Journal
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    • v.18 no.1
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    • pp.53-64
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    • 2008
  • Fouling behavior of polyethylene capillary membranes was examined by measuring the flux of bentonite colloidal suspensions through the cross flow micro filtration. The membrane fouling was due to the three mechanisms: the cake formation on the membrane surface, the standard pore blocking and the complete pore blocking by particles. These mechanisms were simultaneously responsible for the membrane fouling, being significantly governed by the cake filtration. In the total fouling at $1.0kg/cm^2$ TMP condition, the complete blocking was 3.36%, the standard blocking 3.18% and the cake filtration 96.05%. For 1000 ppm feed solution, the complete blocking was 1.71% compared with the standard blocking of 1.90% and the cake filtration of 96.39%. And 96.14% of the total fouling was generated at the initial period of filtration. The cake filtration effect was larger on $0.34{\mu}m$ pore membrane than on $0.24{\mu}m$ pore membrane. With the increase in cross flow velocity, the component fouling decreased by 10.20%, and the ratio of pore blocking to total fouling increased.

Tuning the rheological properties of colloidal microgel controlled with degree of cross-links (가교도가 제어된 콜로이드 마이크로겔의 유변학적 물성 분석)

  • Han, Sa Ra;Shin, Sung Gyu;Oh, Seung Joo;Cho, Sung Woo;Jung, Naseul;Kang, Bu Kyeung;Jeong, Jae Hyun
    • Journal of the Korean Applied Science and Technology
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    • v.36 no.2
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    • pp.645-655
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    • 2019
  • In this study, colloidal microgel with viscoelasticity were prepared by using dispersion containing physical crosslinking agents and microgels with various strengths depending on the degree of cross-links.As the chemical crosslinking agent PEGDA400 content increased, hydrogels have various physical properties the swelling ratio decreased from $2.0{\times}10^4%$ to $6.0{\times}10^3%$ and increased viscosity by about 60%. The colloidal microgel was prepared with micro hydrogel grinded to $100{\mu}m$ size and the rheological behavior was confirmed with physical cross linking agent. A colloidal microgel having various viscosities was prepared by controlling starch and alginate based on micro-hydrogel containing 0.75% (w/v) of PEGDA400. In conclusion, these results would be highly useful for applying as a product that can give various physical properties to the colloidal suspensions, cosmetics, paint, and food industry.