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Hiroyuki Ohshima - One of the best experts on this subject based on the ideXlab platform.

  • Ion size effect on counterion condensation around a spherical colloidal Particle in a salt-free medium containing only counterions
    Colloid and Polymer Science, 2018
    Co-Authors: Hiroyuki Ohshima
    Abstract:

    A theory of counterion condensation around a spherical colloidal Particle in a salt-free medium containing only counterions developed by Imai and Oosawa as reported by Busseiron Kenkyu 52:42, 1952 ibid. 59:99, 1953 ) and later by Ohshima (J Colloid Interface Sci 247:18, 2002 ) is extended to incorporate the ion size effect on the basis of the modified Poisson-Boltzmann equation using the Carnahan-Starling activity coefficient of counterions. The potential distribution depends on the Particle Surface Charge, the Particle volume fraction, and the average counterion volume fraction. It is shown that for a dilute Particle suspension, the counterion condensation occurs, leading to a decrease in the Particle Surface potential when the following two conditions are both satisfied: (i) the scaled Particle Surface Charge is greater than the logarithm of the inverse of the Particle volume fraction and (ii) the average counterion volume fraction is much smaller than the Particle volume fraction.

  • Electrophoresis of colloidal Particles in a salt-free medium
    Chemical Engineering Science, 2006
    Co-Authors: Hiroyuki Ohshima
    Abstract:

    Abstract A general theory for the electrophoretic mobility of dilute spherical colloidal Particles in a salt-free medium containing counterions only is given. This theory assumes that each Particle is surrounded by a spherical free volume, within which electroneutrality as a whole holds. It is shown that the mobility can be obtained from the balance between the Stokes drag for the case where the Particle is unCharged and the pressure due to the excess counterion Charge on the outer boundary of the free volume. The mobility μ is thus expressed as μ = Q exp ( y ( R ) ) / D , where Q is the Particle Surface Charge, D is the drag coefficient of the Particle when unCharged, and y ( R ) is the scaled potential value at the outer boundary of the free volume.

  • Dynamic electrophoretic mobility of spherical colloidal Particles in a salt-free medium.
    Journal of colloid and interface science, 2003
    Co-Authors: Hiroyuki Ohshima
    Abstract:

    Abstract A theory is proposed for the dynamic electrophoretic mobility μ(ω) of spherical colloidal Particles in a salt-free medium containing only counterions in an oscillating electric field of frequency ω. The dynamic mobility depends on the frequency ω of the applied electric field and on the Particle volume fraction as well as on the Particle Surface Charge. It is found that as in the case of the static electrophoretic mobility μ(0) in salt-free media, there is a certain critical value of the Particle Surface Charge separating two cases, that is, the low-Surface-Charge case and the high-Surface-Charge case (in the latter case the counterion condensation takes place near the Particle Surface). For the low-Surface-Charge case, the dynamic mobility agrees with that of a sphere in an electrolyte solution in the limit of very low electrolyte concentrations κa→0 (Huckel's limit), where κ is the Debye–Huckel parameter and a is the Particle radius. For the high-Surface-Charge case, however, the dynamic mobility becomes constant independent of the Particle Surface Charge, because of the counterion condensation effects. A simple expression for the ratio μ(ω)/μ(0) applicable for all cases is given.

  • electrophoretic mobility of a cylindrical colloidal Particle in a salt free medium
    Journal of Colloid and Interface Science, 2002
    Co-Authors: Hiroyuki Ohshima
    Abstract:

    Abstract Approximate expressions are derived for the electrophoretic mobility of dilute cylindrical colloidal Particles in a salt-free medium containing only counterions. The cylinder is assumed to be infinitely long. It is shown that as in the case of a spherical Particle, there is a certain critical value of the Particle Surface Charge separating two cases. When the Particle Surface Charge is lower than the critical value (case 1), the electrophoretic mobility increases with increasing Particle Surface Charge per unit length. When the Particle Surface Charge is higher than the critical value (case 2), the mobility becomes constant (for a cylinder in a transverse field) or the increase in the electrophoretic mobility with the Particle Surface Charge becomes suppressed (for a cylinder in a tangential field). These phenomena are caused by the effect of counterion condensation in the vicinity of the Particle Surface. The critical value of the Particle Charge is essentially independent of the Particle volume fraction φ for the dilute case, unlike the case of a sphere, in which case the critical Charge value is proportional to ln(1/φ).

  • Electrophoretic Mobility of a Spherical Colloidal Particle in a Salt-Free Medium
    Journal of Colloid and Interface Science, 2002
    Co-Authors: Hiroyuki Ohshima
    Abstract:

    A general expression as well as approximate expressions are derived for the electrophoretic mobility of dilute spherical colloidal Particles in a salt-free medium containing only counter ions. It is shown that there is a certain critical value of the Particle Surface Charge. When the Particle Surface Charge is lower than the critical value, the electrophoretic mobility is proportional to the Particle Surface Charge or the Particle zeta potential, following Huckel's formula. When the Particle Surface Charge is higher than the critical value, the electrophoretic mobility becomes independent of the Particle Surface Charge. This is due to the effect of counter ion condensation in the vicinity of the Particle Surface.

Patrick S. Nicholson - One of the best experts on this subject based on the ideXlab platform.

  • Influence of acidity on the stability and rheological properties of ionically stabilized alumina suspensions in ethanol
    Journal of the American Ceramic Society, 2004
    Co-Authors: Gonghou Wang, Patrick S. Nicholson
    Abstract:

    The ionic stability of alumina Particles in moderately concentrated ethanol suspensions is studied. Surface chemistry and interParticle forces are manipulated by controlling the acidity of the suspensions without dispersants. The acidity of ethanol solution is determined using ion transfer functions, wherein the relationships between acidity, alumina Particle Surface Charge, zeta-potential, stability, and suspension rheological behavior are established. Positive isoelectric point (IEP) shift is observed for alumina in ethanol on increasing the solids concentration. However, dilute and concentrated aqueous suspensions of alumina give the same IEP. The viscosity and flow curves for alumina/ethanol suspensions are acidity dependent. The flow curves of the suspensions follow the Casson model, and the Casson yield value is used to evaluate suspension stability.

  • Relative Colloidal Stability in Ethanol of Powders with Si‐O Surface Species
    Journal of the American Ceramic Society, 2004
    Co-Authors: Yoko Fukada, Patrick S. Nicholson
    Abstract:

    The relative colloidal stability in ethanol of ceramic powders with Si-O Surface groups (Si 3 N 4 , SiC, and MoSi 2 ) is reported. SiO 2 /EtOH suspensions are also examined as a reference. The comparative relationships between pH, Particle-Surface Charge, zeta potential, stability, and suspension rheology are discussed. The nature and influence of the Surface species are determined, and the similarities and differences are compared. DLVO theory was used to define suspension stability, and it was found that non-oxide Particles in EtOH are Charge-stabilized and have viscosity and flow curves that agree with the electrokinetic measurements.

  • The role of Si–O species in the colloidal stability of silicon-containing ceramic powders
    Journal of the European Ceramic Society, 2004
    Co-Authors: Yoko Fukada, Patrick S. Nicholson
    Abstract:

    Abstract The relative colloidal stability in ethanol of ceramic powders with Si–O Surface groups (Si3N4, SiC and MoSi2) is reported. SiO2/EtOH suspensions are also examined as reference. The comparative relationships between pH, Particle-Surface Charge, zeta-potential, stability and suspension rheology are discussed. The nature and influence of the Surface species is determined and the similarity/difference therebetween, compared. DLVO theory and Stability Ratio values defined suspension stability and it was found non-oxide Particles in EtOH are Charged-stabilized and have viscosity and flow-curves that agree with the electrokinetic measurements.

Yoko Fukada - One of the best experts on this subject based on the ideXlab platform.

  • Relative Colloidal Stability in Ethanol of Powders with Si‐O Surface Species
    Journal of the American Ceramic Society, 2004
    Co-Authors: Yoko Fukada, Patrick S. Nicholson
    Abstract:

    The relative colloidal stability in ethanol of ceramic powders with Si-O Surface groups (Si 3 N 4 , SiC, and MoSi 2 ) is reported. SiO 2 /EtOH suspensions are also examined as a reference. The comparative relationships between pH, Particle-Surface Charge, zeta potential, stability, and suspension rheology are discussed. The nature and influence of the Surface species are determined, and the similarities and differences are compared. DLVO theory was used to define suspension stability, and it was found that non-oxide Particles in EtOH are Charge-stabilized and have viscosity and flow curves that agree with the electrokinetic measurements.

  • The role of Si–O species in the colloidal stability of silicon-containing ceramic powders
    Journal of the European Ceramic Society, 2004
    Co-Authors: Yoko Fukada, Patrick S. Nicholson
    Abstract:

    Abstract The relative colloidal stability in ethanol of ceramic powders with Si–O Surface groups (Si3N4, SiC and MoSi2) is reported. SiO2/EtOH suspensions are also examined as reference. The comparative relationships between pH, Particle-Surface Charge, zeta-potential, stability and suspension rheology are discussed. The nature and influence of the Surface species is determined and the similarity/difference therebetween, compared. DLVO theory and Stability Ratio values defined suspension stability and it was found non-oxide Particles in EtOH are Charged-stabilized and have viscosity and flow-curves that agree with the electrokinetic measurements.

Parag Bhargava - One of the best experts on this subject based on the ideXlab platform.

  • effect of milling time on the rheology of highly loaded aqueous fused silica slurry
    Journal of the American Ceramic Society, 2008
    Co-Authors: Kalyani Mohanta, Parag Bhargava
    Abstract:

    The effects of milling time on the rheological behavior of 70-vol% loaded fused silica slurries were studied. A transition from shear thickening to shear thinning behavior was observed with milling time. Slurry viscosity and thixotropy attained a minimum after 18 h of milling and remained almost unchanged with additional milling. Infrared spectroscopy and Particle Surface Charge measurements confirmed the development of increasing amount of Surface hydroxide and Surface Charge respectively with progress in milling time, leading to shear thinning behavior. An initial static aging treatment of 24 h aided the development of silanol groups, indicating that the milling time can be reduced to save energy and time.

  • Effect of Milling Time on the Rheology of Highly Loaded Aqueous‐Fused Silica Slurry
    Journal of the American Ceramic Society, 2008
    Co-Authors: Kalyani Mohanta, Parag Bhargava
    Abstract:

    The effects of milling time on the rheological behavior of 70-vol% loaded fused silica slurries were studied. A transition from shear thickening to shear thinning behavior was observed with milling time. Slurry viscosity and thixotropy attained a minimum after 18 h of milling and remained almost unchanged with additional milling. Infrared spectroscopy and Particle Surface Charge measurements confirmed the development of increasing amount of Surface hydroxide and Surface Charge respectively with progress in milling time, leading to shear thinning behavior. An initial static aging treatment of 24 h aided the development of silanol groups, indicating that the milling time can be reduced to save energy and time.

Cesare Cametti - One of the best experts on this subject based on the ideXlab platform.

  • Colloidal Particle aggregates induced by Particle Surface Charge heterogeneity
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009
    Co-Authors: Simona Sennato, Domenico Truzzolillo, Federico Bordi, Francesco Sciortino, Cesare Cametti
    Abstract:

    Abstract Interaction of Charged Particles, induced by adding an oppositely Charged polyion, gives rise to intriguing aggregation phenomena. The presence of short-range interactions in competition with electrostatic repulsions results, in an interval of concentrations around the inversion point, in the formations of long-lived clusters of polyelectrolyte-decorated Particles. We will show that the whole aggregation scenario can be justified as due to an heterogeneous Charge distribution at the Particle Surface, as a consequence of the correlated polyion adsorption, on the basis of a recently model proposed by D. Velegol, P. Thwar, Langmuir 17 (2001) 7687–7693.

  • Colloidal Particle aggregates induced by Particle Surface Charge heterogeneity
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009
    Co-Authors: Simona Sennato, Domenico Truzzolillo, Federico Bordi, Francesco Sciortino, Cesare Cametti
    Abstract:

    Interaction of Charged Particles, induced by adding an oppositely Charged polyion, gives rise to intriguing aggregation phenomena. The presence of short-range interactions in competition with electrostatic repulsions results, in an interval of concentrations around the inversion point, in the formations of long-lived clusters of polyelectrolyte-decorated Particles. We will show that the whole aggregation scenario can be justified as due to an heterogeneous Charge distribution at the Particle Surface, as a consequence of the correlated polyion adsorption, on the basis of a recently model proposed by D. Velegol, R Thwar, Langmuir 17 (2001) 7687-7693. (C) 2009 Elsevier B.V. All rights reserved