Colloid Vibration Potential in a Concentrated Suspension of Spherical Colloidal Particles

A relation between the dynamic electrophoretic mobility of spherical colloidal particles in a concentrated suspension and the colloid vibration potential (CVP) generated in the suspension by a sound wave is obtained from the analogy with the corresponding Onsager relation between electrophoretic mobility and sedimentation potential in concentrated suspensions previously derived on the basis of Kuwabara's cell model. The obtained expression for CVP is applicable to the case where the particle zeta potential is low, the particle relative permittivity is very small, and the overlapping of the electrical double layers of adjacent particles is negligible. It is found that CVP shows much stronger dependence on the particle volume fraction φ than predicted from the φ dependence of the dynamic electrophoretic mobility. It is also suggested that the same relation holds between the electrokinetic sonic amplitude of a concentrated suspension of spherical colloidal particles and the dynamic electrophoretic mobility. Copyright 1999 Academic Press.     

Electrical Conductivity of a Concentrated Suspension of Spherical Colloidal Particles

A general expression for the electrical conductivity of a concentrated suspension of spherical colloidal particles is obtained for the case where the particle zeta potential is low and the overlapping of the electrical double layers of adjacent particles is negligible by using Kuwabara's cell model. It is shown how the conductivity of a concentrated suspension depends on the particle volume fraction, the zeta potential zeta, and the reduced particle radius kappaa (kappa = Debye-Hückel parameter and a = particle radius). It is also found that the obtained conductivity formula tends to Maxwell's formula for two different extreme cases: (i) when the particles are uncharged (zeta = 0) and (ii) when the electrical double layers around the particles are infinitesimally thin (kappaa --> infinity). That is, in the latter limiting case (kappaa --> infinity), the conductivity becomes independent of the zeta potential, just as in the case of dilute suspensions. Copyright 1999 Academic Press.     

Primary Electroviscous Effect with a Dynamic Stern Layer: Low kappaa Results

The classical treatments of the primary electroviscous effect show important discrepancies with respect to the experimental data. A possible better agreement may be found if the contribution of the ions adsorbed on the Stern layer, which can move tangentially near the particle surface, is taken into account. This contribution has been incorporated into the Watterson-White theory. A study of the influence of the Stern-layer parameters on the primary electroviscous coefficient has been made. Copyright 2000 Academic Press.     

Low-Shear Viscosities of Dilute Dispersions of Colloidal Rodlike Silica Particles in Cyclohexane

Low-shear viscosities have been studied for isotropic dispersions of uncharged colloidal silica rods in cyclohexane as a function of volume fraction Φ and aspect ratior_p. Intrinsic viscosities in the limit Φ → 0 agree with theoretical results [Brenner, H.,Int. J. Multiphase Flow1,195 (1974)] for colloidal cylinders. The Φ²term in the low-shear viscosity, accounting for two-particle interactions, is considerably larger than predicted by D. H. Berry and W. B. Russel [J. Fluid Mech.180,475 (1987)] for dilute hard-rod dispersions. The discrepancy is very likely due to weak interparticle attractions, which also account for the novel observation of an isotropic–isotropic phase separation in the silica rod dispersions. Our results demonstrate that, in comparison to spheres, high aspect ratios markedly increase both the shear viscosity and its sensitivity to even minor attractions.     

The Effect of Polydispersity on the Size of Colloidal Particles Determined by the Dynamic Light Scattering

An attempt is made to allow for a sample polydispersity while measuring particle size distribution by the dynamic light scattering. The scattering ability R(r) is calculated for monodisperse samples and samples with rectangular, bell-shaped, and triangular (increasing and decreasing) particle size distributions. It is shown that, when the processing program for the data of light bearing spectroscopy assumes a linear scale of particle sizes, the scattering ability, irrespective of the distribution pattern, is proportional to the sixth power of the particle size for the Rayleigh region and to the second power, for larger particles. However, when the scale of the half-width of the Rayleigh spectrum is linear, the pattern of the curve describing the particle scattering capability substantially changes upon passing from monodisperse to polydisperse samples. This curve can be approximated by a function R r ⁷ in the Rayleigh region and by a function R r ³ in the range of large (as compared with the wavelength) particles.     

Dynamic Mobility of Particles with Thick Double Layers in a Nondilute Suspension

The dynamic mobility of a nondilute suspension of spherical particles is investigated in the case where the thickness of the electrical double layer around each particle is comparable to the particle radius. A formula is obtained for the O(φ) correction in a random suspension of particles with volume fraction φ, involving an integral over the dynamic mobility of a pair of spheres. This formula is then evaluated using both analytical approximations and numerical results previously obtained for the pair mobilities and valid for low surface potentials. The effect of double-layer thickness on the O(φ) coefficient is most pronounced at low frequencies, and lessens once the hydrodynamic penetration depth is smaller than the particle radius. Various approximations are considered that use the O(φ) result to predict the dynamic mobility in concentrated suspensions, and at high frequencies these approximations are shown to give results qualitatively different from those of recent cell models. Copyright 2000 Academic Press.     

Investigation of Dynamic Stern Layer of Liposomes by Measurements of Conductivity and Electrophoresis

Ionic surface diffusitivity is important parameter for the electrostatic interaction between colloid particles and hence its measurement is a new important factor for the surface characterization of colloid particles. If the adsorbed ion mobility is small the approximation of the interaction at constant charge can be valid,but in opposite case the charge regulation occurs during their interaction.

The large surface diffusitivities of polyvalent ions adsorbed on negatively charged liposomes are found combining measurements of conductivity and electrophoresis. At a rather low surface charge and high adsorbability of polyvalent cations, the diffuse-layer charge can be very small in comparison with the Stern-layer charge, which can predominate in surface conductivity and provide information about the diffusitivity of adsorbed ions if it is not small. An efficient and simple method for the discrimination between small and large surface diffusitivities of adsorbed ions based on the determination of both iso-electric point and iso-conducting point is proposed and experimentally proved.     

Sedimentation Velocity and Potential in Concentrated Suspensions of Charged Spheres with Arbitrary Double-Layer Thickness

The sedimentation in a homogeneous suspension of charged spherical particles with an arbitrary thickness of the electric double layers is analytically studied. The effects of particle interactions are taken into account by employing a unit cell model. Overlap of the double layers of adjacent particles is allowed, and the polarization effect in the double layer surrounding each particle is considered. The electrokinetic equations that govern the ionic concentration distributions, the electric potential profile, and the fluid flow field in the electrolyte solution in a unit cell are linearized assuming that the system is only slightly distorted from equilibrium. Using a perturbation method, these linearized equations are solved for a symmetrically charged electrolyte with the surface charge density (or zeta potential) of the particle as the small perturbation parameter. An analytical expression for the settling velocity of the charged sphere in closed form is obtained from a balance among its gravitational, electrostatic, and hydrodynamic forces. A closed-form formula for the sedimentation potential in a suspension of identical charged spheres is also derived by using the requirement of zero net electric current. Our results demonstrate that the effects of overlapping double layers are quite significant, even for the case of thin double layers. Copyright 2000 Academic Press.     

Clustering of Particles in Colloidal and Molecular Fluids

Abstract

A review is given of the nature and implications of cluster formation in colloidal and molecular systems. We consider large clusters that can be described in terms of the fractal dimension and percolation exponents. The role of computer molecular simulation is discussed as a new method for probing random clustering of particles, short range structural correlations being of diminished importance here.     

The Primary Electroviscous Effect: Thin Double Layers (akappa>1) and a Stern Layer

The primary electroviscous effect due to the charge clouds surrounding spherical charged particles suspended in an electrolyte was studied by Hinch and Sherwood (J. Fluid Mech. 132, 337 (1983)) in the limit of double layers thin compared to the particle radius a. Here we introduce the effect of a dynamic Stern layer into that analysis, in order to explain the numerical results of Rubio-Hernández et al. (J. Colloid Interface Sci. 206, 334 (1998)) in terms of the ratio of the tangential ionic fluxes within the charge cloud to those within the Stern layer. The predictions of the asymptotic analysis are compared with those of numerical computations. The thickness of the charge cloud is characterized by the Debye length kappa(-1). If akappa>10 the predictions of the asymptotic analysis exhibit the same qualitative behavior as the numerical results, but akappa>1000 is required to achieve quantitative agreement to within 2.5%. Copyright 2000 Academic Press.     

An Enthalpic Analysis on the Aggregation of Colloidal Particles Studied by Microcalorimetry

There are different theories concerning the stability of colloidal suspensions. Most of them arise from the well-known DLVO theory which relates colloidal stability to intermolecular forces between particles. Experimental corroboration of these theories has been obtained mainly by using different optical techniques that analyze changes in the optical properties of the solution while particles aggregate. However, no attention has been paid to studying the aggregation process thermodynamically. This is why we have focussed on studying the heat released during the agglutination of polystyrene particles. The enthalpy change in this aggregation process was detected by using a highly sensitive and modern technique called isothermal titration calorimetry. In addition, some results about repeptization, that is, reversibility in the aggregation process, are also shown. Copyright 2001 Academic Press.     

受限混合物溶剂中胶粒的耗尽势及吸附稳定性

基于密度泛函理论和Yvon-Born-Green方程得到了胶粒耗尽势的表达式.采用密度泛函理论计算了单壁附近和平行狭缝中的混合物溶剂中胶粒的耗尽势及其在单壁处的吸附稳定性.研究结果表明,不同溶剂组分的体积分数和粒子尺寸比等因素对胶粒耗尽势的强度、力程和周期均可产生显著影响,胶粒在单壁附近的吸附稳定性与溶剂粒子尺寸比和体积分数密切相关.此外,对受限于平行狭缝的胶体悬浮液,胶粒的耗尽势阱还可随粒子尺寸比和缝宽呈振荡趋势变化.     

Laser-Induced "Regeneration" of Colloidal Particles: The Effects of Thermal Inertia on the Chemical Reactivity of Laser-Heated Particles

A size reduction of the suspended particles is observed upon irradiation of colloidal metal solutions by a high-power, pulsed laser, resulting in dramatic changes in their optical properties. The mechanism of change involves rapid production of ions as a consequence of laser heating, followed by diffusion and chemical reduction on a long time scale to form new colloidal particles. The process, by which large particles are differentially consumed relative to small ones, depends on the "thermal inertia" of the particles, which governs the temperature of the particles and hence their reactivity.     

Kinetics of the Growth of Supramolecular Crystals in a Suspension of Monodisperse Spherical Silica Particles

Kinetics of the supramolecular crystallization of monodisperse spherical silica particles (MSSP) suspended in diethyl ether with a concentration of structural units close to the phase transition point has been studied for the first time. It was found that the linear crystal growth rate depends on temperature and the process activation energy is 25 kcal/mol. The linear law of crystal growth is associated with diffusion of the structural units on the interface.     

Modeling the Operation of a Microseparator Taking into Account the Changes in the Thickness of the Stern Layer on the Surfaces of Electrode Pores

Russian Journal of Physical Chemistry A - Mathematical modeling is used to study the deionization dynamics of an electrolyte solution via sorption on aerogel electrodes. The transfer of mass by the...     

Sedimentation of Kaolin Suspension in the Presence of Praestol Anionic Flocculant and Aluminum Polyoxychloride and Sulfate Coagulants

The kinetics of sedimentation of kaolin suspension in the presence of coagulants (aluminum polyoxychloride and sulfate) and Praestol anionic flocculant was studied, as influenced by the concentrations of coagulants and flocculant, mode and time of their addition into the suspension, composition of the coagulant mixture, and chemical structure and conformation of flocculant macromolecules.