Primary Electroviscous Effect Research Articles

The primary electroviscous effect in monodisperse polystyrene suspensions

AbstractAn experimental investigation of the electrokinetic phenomena known as primary electroviscous effect with suspensions of polystyrene spheres is described. A characteristic coefficient of the effect has been measured by an automatic method for the determination of the viscosity of liquids through capillary viscometers. In order to compare this coefficient with the values predicted by different theoretical models, the electrophoretic mobility of the spheres was measured by means of a microelectrophoresis apparatus. The zeta potential was calculated from the results with a complete theory of the electrophoresis of spherical particles. The comparison between theoretical and experimental values of the electroviscous effect shows that the theories of Booth and of Watterson and White reproduce very well the general trend of the experimental results, althogh they seem to underestimate the latter.

The primary electroviscous effect in surfactant-free polystyrene lattices: The effect of increasing concentrations of quaternary ammonium counterions of different ionic sizes

The primary electroviscous effect and ζ potentials in two different series of polystyrene lattices of increasing particle size, prepared without addition of surfactants, have been measured, in the presence of increasing concentrations of quaternary ammonium counterions of different ionic sizes. It has been found that whereas for the larger particle size lattices the measured electrical contribution to the primary electroviscous effect ( η el / η 0 φ) = ( η − η 0)/ η 0 φ − 2.5) decreases with increasing counterion concentration, as required by the theory, it either remains more or less constant or increases slowly in the case of smaller particle size lattices due possibly to the simultaneous occurrence of a slow feeble agglomeration of the latex particles in the presence of increasing counterion concentrations. Stability calculations according to the DLVO theory tend to support this conjecture. The electrophoretically measured ζ potentials show a steady decrease with increasing counterion concentration; a Langmuir-type isotherm relating the decrease of charge density in the Stem plane with the added counterion concentration has been found to be mostly able to account for the observed results.

The primary electroviscous effect in a suspension of spheres with thin double layers

We study the primary electroviscous effect in a suspension of spheres when the double layer thickness κ−1 is small compared with the particle radius a. The case of a 1–1 symmetric electrolyte is examined using the methods of Dukhin & coworkers (1974), whilst the asymmetric electrolyte is studied along lines similar to those of O'Brien (1983). Sherwood's (1980) asymptotic results for high surface potentials and high Hartmann numbers are extended and complemented.

The Primary Electroviscous Effect

Measurements of the viscosity of a suspension of monodisperse polystyrene particles as a function of volume fraction at two fixed values of κa (3.13 and 8.24) and various values of the electrokinetic (ζ−) potential permit a test of current theories of the primary electroviscous effect. The results reveal a major discrepancy which may be real but which is more likely attributable to the presence of a “gel‐like” layer on the surface of these particles.

The primary electroviscous effect in ageing AgI sols: Effect of increasing concentrations of counter ions of different valencies

The electroviscous effect in negatively charged AgI sol has been measured in presence of uni-, bi-, and trivalent cations at different concentrations, for a constant low volume fraction of the suspended solid particles. The I − ion activity of the sol (and also the particle size) gradually increased due to ageing effect during the entire course of study over a period of several months, but remained effectively constant during each course of study (over a few days) with any particular counterion. The potentials were simultaneously measured electrophoretically at identical electrolyte and I − ion concentrations. The electrical (double layer) contribution to the viscosity of the sol was calculated for various values of q o for each electrolyte. A close correspondence has been found in each case with the potential results.

The primary electroviscous effect in a suspension of rods

Previous studies of the distortion of the electric double layer around a charged sphere have assumed that the electric stresses are small compared with the viscous stresses. The flow around the particle is therefore changed only slightly by the presence of the charge cloud. This change is measured by the Hartmann number, and in § 6 we remove the restriction that it should be small. It is found that the previous linearized theory is sufficiently accurate for typical experimental values of the Hartmann number. Previous studies have also assumed that the potential at the surface of the particle is small. This assumption is removed in § 7 of this paper. For values of the non-dimensional surface potential smaller than 2 the predictions are altered by less than 10 %. For higher values the differences between linear and nonlinear theory are not negligible, especially when the charge cloud is thin compared with the radius of the charged sphere.

Primary electroviscous effect in suspensions of charged spherical particles

The effective viscosity η of a suspension of charged spherical colloidal particles in a general electrolyte of viscosity η0 is calculated to first order in the volume fraction ϕ to be η=η0{1 + 5/2ϕ[1 +p(ζ, κa)]}. The primary electroviscous coefficient p(ζ, κa) as a function of the zeta potential ζ is derived in terms of the asymptotic behaviour of the hydrodynamic flow field far from a typical colloidal particle. The computation of p(ζ, κa)(for a general mixed electrolyte with ζ unrestricted in magnitude) is reduced to the solution of a set of linear coupled ordinary differential equations and an accurate and robust numerical scheme for solving them is demonstrated. An analytic approximate expression for p(ζ) correct to (ζ2) is derived and shown to agree with an early result of Booth. Exact numerical results are compared with the approximate expression of Booth.A maximum is predicted in the primary electroviscous coefficient p(ζ) for all κa values. The measurement of the magnitude of this maximum may be used to test the validity of the underlying equations.

The primary electroviscous effect in a suspension of spheres

Previous studies of the distortion of the electric double layer around a charged sphere have assumed that the electric stresses are small compared with the viscous stresses. The flow around the particle is therefore changed only slightly by the presence of the charge cloud. This change is measured by the Hartmann number, and in § 6 we remove the restriction that it should be small. It is found that the previous linearized theory is sufficiently accurate for typical experimental values of the Hartmann number. Previous studies have also assumed that the potential at the surface of the particle is small. This assumption is removed in § 7 of this paper. For values of the non-dimensional surface potential smaller than 2 the predictions are altered by less than 10 %. For higher values the differences between linear and nonlinear theory are not negligible, especially when the charge cloud is thin compared with the radius of the charged sphere.

The Primary Electroviscous Effect Some Numerical Estimates from Booth's Theory

The Primary Electroviscous Effect Some Numerical Estimates from Booth's Theory

Electroviscous effects of concentrated polystyrene latexes

Abstract Monodisperse polystyrene latexes with immobilized surface charge groups were used in the study of electroviscous effects of colloidal suspensions. The flow curves of the latexes at solids concentrations 15%–40% by weight and at salt concentrations 10−8-10−1 M NaCl have been determined over shear rates 102-104 sec−1. The latexes at these solids and salt levels were all shear thinning. The viscosity-concentration relationship at any given shear rate was shown to obey Mooney's equation: ln η η 0 = αθ 1−Kθ where the intrinsic viscosity α and the crowding factor k depend on the ionic strength and shear rate. The intrinsic viscosity approaches 2.65 ± 0.02 at high shear rates regardless of the ionic strength. This value compares favorably with the intrinsic viscosity 2.5 theoretically calculated by Einstein for noninteracting spheres, indicating that the primary electroviscous effect vanishes at high shear rate. The slightly higher value than the Einstein constant is attributed to the presence of an emulsifier layer of approximately 16 A thickness. The crowding factor k varies from 1.03 to 1.88 depending on the shear rate and ionic strength. The extrapolated value 1.03 for k at high shear rate, however, is much smaller than the value of 1.35–1.91 estimated by Mooney for noninteracting spheres. The electroviscous effects were shown to be well represented by those of an increase in hydrodynamic volume of the particles. The apparent increase in particle radius was experimentally determined as a function of shear rate and ionic strength, and found larger than the Debye-Huckel double layer thickness 1/κ at shear rates less than ∼1000 sec−1. At shear rates above ∼1000 sec−1 the apparent increase in particle radius is smaller than, and linearly related to, the double-layer thickness 1/κ.

Electroviscous effects in dispersions of monodisperse polystyrene latices

Abstract The contribution of electroviscous effects to the viscosity of monodisperse polystyrene latices has been studied. The sols were prepared by emulsion polymerization using as emulsifier a weak acid soap and a strong acid soap, respectively. Particle sizes were determined by electron microscopy and turbidimetry. Excellent agreement between the two methods was obtained. Zeta potentials and charges of the electrokinetic unit were deduced from electrophoretic mobility measurements at different ionic strengths. The validity of the Einstein equation was demonstrated for perfectly stable latices when the primary electroviscous effect can be considered as negligible. Influences of ζ potential, particle charge, ionic strength, particle size, and rate of shear on the first- and second-order electroviscous effects have been investigated. For the primary electroviscous effect, a good agreement with the Booth Street's equation yielded too low viscosities, values predicted by the recent treatment of Chan, Blachford, and Goring were too high. However, this last theory represents a more realistic approach than the Street one.

The primary electroviscous effect in a sulfonated polystyrene latex

The primary electroviscous contribution to the viscosity of suspensions of sulfonated polystyrene latex particles was determined at ionic strengths between 10 −3 and 10 −4 M and shear rates of 650, 9,000, and 16,000 sec. −1. The absence of particle expansion at lower ionic strengths was confirmed by light scattering. The ζ potentials of the sulfonated latex particles at different ionic strengths were determined from measurements of electrophoretic mobility. The observed primary electroviscous effect was compared directly with the theoretical predictions of the equations of Smoluchowski and of Booth. In accordance with theory, the observed effect increased with decreasing ionic strength and was virtually independent of the large change in shear rates. But the results also indicated that whereas Smoluchowski's equation yielded too high an electroviscous effect, values predicted by Booth's expressions were somewhat low.