Primary Electroviscous Effect Research Articles

Effect of Additive NaCl on Rheological Characteristics of Synthetic Hectorite Aqueous Suspensions.

The rheological characteristics of synthetic hectorite/water suspensions have been measured by a cone-plate rheometer as a function of additive NaCl concentration (CNaCl). The hectorite particles, dialyzed preliminarily to remove electrolytic impurities involved, were utilized for preparing a 2.0 wt% aqueous suspension. The apparent viscosities of the suspensions decreased monotonically with increasing CNaCl; these changes in the viscosities came from the primary electroviscous effect. In dynamic viscoelastic measurements of the suspensions, we found that the critical strain also decreased with increasing CNaCl. By the use of a Cryo-SEM, we observed that different types of the particle-coagulated structures in the various suspensions with respective NaCl concentrations. These findings can be explained by the different interaction modes originated from the electrostatic charge near the surface of hectorite particles, as in the following situations : (1) in the low CNaCl region, the electrostatic repulsion among the particles leads effectively to form an expanded network structure in the system; (2) in the high CNaCl region, the van der Waals attraction force among the particles governs the interaction mode in the system, thus resulting to form a dense-packed coagulation structures.

Anomalous Trends in the Electroviscous Effect of Polystyrene Latexes: Experimental and Theoretical Study

In this work the primary electroviscous effect was determined for two polystyrene latexes with different surface charge densities and functional groups (sulfonate and carboxylate). For each latex, the electroviscous coefficient (p) was obtained for several electrolyte (NaCl) concentrations; that is, as a function of the electrokinetic radius κa. In both cases, a maximum in the p against κa plot was found experimentally, which was not predicted by the theory. A study using Booth's and Watterson−White's theories was done to explain the initial differences between experimental and theoretical data at low κa values. These maximum values were theoretically explained as a consequence of a third ionic species present in the solution.

The Primary Electroviscous Effect: Thin Double Layers (aκ⪢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 κ−1. If aκ>10 the predictions of the asymptotic analysis exhibit the same qualitative behavior as the numerical results, but aκ>1000 is required to achieve quantitative agreement to within 2.5%.

The electroviscous effect in ethylcellulose latex suspensions. Effect of ionic strength and correlation between theory and experiments

This article describes an experimental and theoretical investigation of the so-called primary electroviscous effect, i.e., the increase in suspension viscosity due to the existence of an electrical double layer around the particles. By measuring the viscosity of ethylcellulose latex suspensions, the electroviscous coefficient, the quantity measuring the effect, was estimated for different concentrations of 1-1 electrolyte in the dispersion medium. These data were compared with the predictions of Watterson and White's model, using the zeta potential of the particles deduced from electrophoretic mobility measurements. It was found that the theory considerably underestimates the effect. In an attempt to improve the agreement between data and predictions, the model was generalized to include the possibility (dynamic Stern layer) that ions in the inner part of the double layer have nonzero mobility. The general theory, however, predicts even lower values of the electroviscous coefficients, thus increasing the separation between calculated and measured electroviscous coefficients. A careful analysis of the ionic concentrations and velocity profiles with and without dynamic Stern layer corrections can account for this fact, but leaves unsolved the problem of the large discrepancies found in the theoretical explanation of the strength of the electroviscous effect.

Primary Electroviscous Effect with a Dynamic Stern Layer: Low κa 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.

The primary electroviscous effect in polystyrene latexes with variable charge

The primary electroviscous effect in polystyrene latexes with variable charge

An experimental study on the influence of a dynamic Stern-layer on the primary electroviscous effect

The most recent theory by Watterson and White for the primary electroviscous effect of a suspension of charged spherical particles has been extended by considering the influence of a dynamic Stern-layer. In this work we have tested the theoretical results by measuring the viscosity of polystyrene suspensions in different electrolyte concentrations. Zeta potential values have been obtained by electrophoresis and conductivity experiments using the theoretical approachs by Mangelsdorf and White that include the Stern-layer conductance. In order to obtain the same potential values calculated from these two independent methods, we have fitted the Stern-layer parameters of our systems. These parameters and zeta values have been used to calculate the theoretical viscosity. The theoretical results have been compared with the experimental viscosity data obtained with a semiauthomatic Ubbelohde capillary viscometer. We can conclude that the dynamic Stern-layer model used in this work has only a slight influence on the correction of the primary electroviscous effect theory due to Watterson and White. We suggest to study the correction supplied by another dynamic Stern-layer model due to Dukhin and Semenikhin, considering its success when is applied to electrophoresis.

Electroviscous effect of rodlike polyelectrolytes in strong flow

Primary electroviscous effect of a dilute solution of rodlike polyelectrolytes subject to a strong shear flow is investigated theoretically. A linear charge distribution along the macromolecule is assumed in this study. Also the Hartmann number and the ion Peclet number are assumed small so that the electrical body force gives small perturbation to the imposed flow, and the double layer deviates slightly from its equilibrium state. The distortion of the double layer not only gives rise to electrical stresses but also modifies the orientation distribution of the macromolecules, leading to an indirect contribution to the stress. This modification was treated as small perturbations to the orientation distribution of uncharged rods for weak and moderate flows in the previous work. The perturbation analysis, however, becomes invalid for strong flows, in which the rotational flux of the rods due to the charge effect is comparable to their Brownian diffusion and the advection by the fluid in a boundary layer region near the flow direction. In this study, a spherical harmonic method is used to solve for the orientation distribution of the rods by specifying the parameters associated with the charge effect. The results show that the moments of the orientation distribution and the stress stemming from the electrical effect do change in strong flow, in comparison with those obtained from a regular perturbation method.

Chain conformation and intermolecular interaction of partially neutralized poly(acrylic acid) in dilute aqueous solutions

The isoionic dilution method was used to measure the intrinsic viscosity, [η], and the Huggins coefficient, K H, of two poly(acrylic acid) samples, 50% neutralized with NaOH, with molecular weights 5.0×10 3 (Na50PA5) and 4.8×10 4 (Na50PA48) at different ionic strengths. For Na50PA5 at low ionic strength, [η] is higher than the value predicted by a rigid-rod model. Assuming that the chain has reached its maximum extension, we have combined the rigid-rod model with the idea of effective dimensions that depend linearly on the Debye–Hückel screening length, κ −1, to account for a primary electroviscous effect, as a means to describe the observed behavior. As a consistent approach, we have also combined the effective dimensions with the wormlike chain model to calculate the persistence length of the higher molecular weight sample, Na50PA48. The result is that the electrostatic persistence length, l e, is proportional to κ −1, in the region of high to moderate ionic strength, as is usually observed experimentally for flexible polyelectrolytes, while at the lowest ionic strengths, l e tends to level off, which was predicted theoretically. Both the samples show a considerable increase in the Huggins coefficient as the ionic strength is lowered, with the sample having the lowest molecular weight giving the highest value at any particular ionic strength. This is attributed to the increasing intermolecular electrostatic interactions, which have a relatively larger importance in the case of Na50PA5, because the dimensions of the chain are smaller when compared with the range of the electrostatic interactions, as measured by κ −1, than for Na50PA48.

The primary electroviscous effect of polystyrene latexes

An investigation on the primary electroviscous effect of polystyrene latexes has been made. Capillary viscometers of Ubbelohde type have been used. The comparison of the results obtained with the theories allow us to conclude that the effect is underestimated for low electrolyte concentrations. We suggest that this underestimation is due to an additional surface conductance into the electric double layer. This interpretation is consistent with previous studies on electrophoretic mobility of the same system.

The Primary Electroviscous Effect in Polystyrene Latices of Small Particle Size Range Prepared with the Addition of Anionic Surfactant as Emulsifier. Effect of Increasing Concentrations of Quaternary Ammonium Counterions of Different Ionic Sizes and Stability Characteristic of the Latices and the Latex–Electrolyte Mixtures

Polystyrene latices were prepared by the emulsion polymerization method using hydrogen peroxide as an initiator and sodium dodecyl sulfate as the emulsifying agent. Latices of different particle sizes were prepared by the seeded growth technique. The particle size and its frequency distribution were determined by electron microscope. The viscosities and electrophoretic mobilities of the latex and latex:added electrolyte mixtures were measured in the presence of gradually increasing concentrations of quaternary ammonium counterions of different ionic sizes. The ζ-potentials were calculated by the computational method of Wiersema–Loeb– Overbeek (WLO); the surface charge densities σ were calculated by the method of Loeb–Wiersema–Overbeek (LWO). The primary electroviscous effects were calculated by using the Booth equation. The free energies of adsorption ΔḠadsof the counterions on the particle surface were calculated. The stability characteristic of the latices and latex–added electrolyte mixtures has been studied on the basis of the DLVO theory.

The Primary Electroviscous Effect of Rigid Polyions of Arbitrary Shape and Charge Distribution

The viscosity of a dilute suspension of charged rigid particles exceeds that of a suspension of identical, but uncharged particles, and this is called the primary electroviscous effect. This excess viscosity arises as a result of the distortion of the ion atmosphere surrounding the polyion due to the fluid shear field in which it is placed. Consequently, any theory of the primary electroviscous effect must account for this distortion. Booth (Proc. Roy. Soc. (London) 1950, 203A, 533) and later Sherwood (J. Fluid Mech. 1980, 101, 609) achieved this for a spherical polyion of uniform equilibrium surface potential by solving the coupled (low Reynold's number) Navier-Stokes, Poisson, and ion transport equations. The primary objective of the present work is to extend this approach to rigid model polyions of arbitrary shape and charge distribution. The coupled transport equations are solved by an iterative boundary element (BE) procedure applied previously to the closely related problem of electrophoresis (Allison, S. A. Macromolecules 1996, 29, 7391). In test cases on spheres containing single central charges, the BE results are found to be in very good agreement with Sherwood. The BE approach is then applied to spherical polyions containing noncentrosymmetric charge distributions as well as short (20-40 base pair) DNA models in the monovalent salt range 0.005-0.6 M. For the DNA fragments, the primary electroviscous effect ranges from about 2% to 30% (40 bp) or 45% (20bp) as the KCI concentration is reduced from 0.6 to 0.005 M, respectively. Substantially larger effects are predicted if the monovalent salt is Tris-acetate, and this is due primarily to the lower mobility of the Tris counterion relative to K + . A secondary objective is to make contact between the BE approach and bead methods, which have been successfully used in modeling the viscosity of rigid, but uncharged macromolecules of arbitrary shape.

Viscosity of a Dilute Suspension of Sodium Montmorillonite in a Electrostatically Stable Condition

The viscosity of a dilute suspension of sodium montmorillonite under dispersed conditions was measured as a function of electrolyte concentration using a capillary viscometer. Analyses were focused on the evaluation of electroviscous effects. The absence of particle expansion due to swelling was confirmed by the Stokes diameter measured by photon correlation spectroscopy (PCS). The intrinsic viscosity obtained was found to increase with an increase of reciprocal Debye length (κ−1) which demonstrated the evidence of a primary electroviscous effect. By extrapolating this relation to κ−1= 1 nm, we obtained the intrinsic viscosity [η] free from the electroviscous effect. Using this value, the shape factor and size of the montmorillonite sheet were estimated. The estimated size was slightly smaller than that obtained from PCS. The viscosity data also suggested the importance of the multiparticle interaction which appeared in accordance with an increment in double layer thickness. At lower electrolyte concentration, we found a larger Huggins’ coefficient, which is an index of the degree of pair interaction, and we found that the multiparticle interaction appeared at a lower volume fraction of clay sheets.

On the solution viscosity of ionic polymers and their conformation in solutions

The viscosity behavior of linear, flexible ionic polymers in solutions and its accepted interpretation were discussed. Experimental viscosity data by Yamanaka et al. were pointed out to show the α value of the Houwink-Mark-Sakurada equation being smaller than two, a value expected for rod-like conformation. The viscosity of latex dispersions, telechelic polymer solutions, and microgel dispersions showed that the intra-molecular interaction does not play a role as important as was supposed to be in the previous argument. The Booth theory of primary electroviscous effect of charged particles (distortion of ion cloud under flow) was found to be satisfactory in explaining dependencies of viscosity of colloidal particles on charge number (Q), size, and salt concentration, particularly for large κa (1/κ: Debye's radius, a: the particle radius) and at small Q. Taking into consideration that the macroion domain corresponds to extremely high concentrations of ionic groups, the formation of multiple ions by a counterion-mediated attraction, which was not considered so far, was tentatively suggested. Further, the contribution of localized ordered domains of macroions that were recently unveiled was suggested to be presumably influential in viscosity properties.

The primary electroviscous effect in silica suspensions. Ionic strength and pH effects

An experimental investigation of the electrokinetic phenomenon known as the primary electroviscous effect is described. A characteristic coefficient for the effect has been measured in spherical silica suspensions by means of an automatic method for the determination of the viscosity of liquids using capillary viscometers. The effects of the pH and the KCl concentration are investigated, and the electrophoretic mobilities and zeta potentials of the particles are determined under the different experimental conditions. A comparison between theoretical and experimental values of the electroviscous coefficient demonstrates that the most elaborate models reproduce the trends in variation of the data, although they significantly underestimate the latter. At pH 8 and 9, theory and experiment disagree; this is explained by a hypothesis of silica dissolution.

A Spherical Particle Surrounded by a Thin Double Layer in a Simple Shear Flow

The electric, concentration, and hydrodynamic fields which arise in the neighborhood of a charged spherical particle with a thin double layer in shear flow have been calculated, together with the primary electroviscous effect. Rotation of a charged particle results in the creation of an induced electric quadrupole moment. It is shown that, unlike polarization in an electric field, the motion of a particle in a hydrodynamic flow field causes a concentration polarization (relaxation effect) even when the surface conductivity is small. The concentration field extends beyond the double layer and also features a quadrupole symmetry. An increase of surface conductivity is accompanied by a decrease in the magnitude of the electric and hydrodynamic polarization fields. For spherical particles with thin double layers the primary electroviscous effect has been calculated for arbitrary values of the ζ potential. It is found that the intrinsic viscosity increases with the ζ potential for low potentials, but decreases at high potentials. The reason is that an increase in the ζ potential is accompanied by an increase in surface conductivity. It is possible to generalize the analytical theory to a more general double layer model in which the ζ potential is not the same as the Stern potential.

The Primary Electroviscous Effect in Surfactant Free Polystyrene Lattices. II. The Effect of increasing Concentrations of Quaternary Ammonium Counterions of different Ionic Sizes

The Primary Electroviscous Effect in Surfactant Free Polystyrene Lattices. II. The Effect of increasing Concentrations of Quaternary Ammonium Counterions of different Ionic Sizes

The rheology and microstructure of charged colloidal suspensions

The effects of electric charge interation and particle correlations on suspension rheology are examined. A one-component fluid analysis using a Smoluchowski equation for the equilibrium structure is applied to charged suspensions of spherical colloids under shear. The frequency dependent modulus and viscosity, predicted as functions of particle and added salt concentrations, are compared with published rheological measurements on model suspensions. Recent improvements in the statistical mechanical theories for the equilibrium microstructure, its nonequilibrium deformation, and the bulk shear stresses are included. The direct electrostatic interaction is found to drive the divergence in the shear viscosity near the liquid-solid phase transition. Extensions of the theory predict the elastic modulus of binary mixtures of charged colloids. Estimates of the primary electroviscous effect, hydrodynamic interactions, and errors in the Yukawa limiting form for the potential and applications of asymptotic theories are presented. Predictions for the rheology based on effective hard-sphere models are found to be reasonable when using a parameter fit from the equilibrium phase behavior. Mean-field mode coupling theories predict larger relaxation times than calculated from the Smoluchowski equation (=SE). A study of binary mixing effects on elasticity shows non-ideal behavior. It is noted that equilibrium structural information can be used to resolve discrepancies between the theoretical predictions and the measured rheology.

The primary electroviscous effect: Measurements on silica sols

The dependence of the viscosity of silica (ludox) sols on the electrolyte concentration of various aqueous solutions has been determined. At volume fractions below 5% the sols were Newtonian and the viscosity was proportional to the volume fraction of the particles. The (large) deviations from the Einstein equations can be explained very well with the effective increase of the particle volume due to the electrical double layer, as described by the Booth equation for the primary electroviscous effect.

A STUDY OF THE PRIMARY ELECTROVISCOUS EFFECT IN PYREX GLASS SUSPENSIONS.

ABSTRACT An experimental investigation on the electrokinetic phenomenon known as primary electroviscous effect is described for suspensions of Pyrex glass, a highly charged and well known material. By means of an automatic method, the viscosity of the suspensions is measured for different volume fractions of solids, at various electrolyte concentrations and pH values. These measurements allow the estimation of the electroviscous coefficient, p. The electrophoretic mobility was determined for the same systems and zeta potential calculated from these experimental data in order to carry out the comparison between the measured values of p and different theoretical predictions. A qualitative agreement between theory and experiment was found in many cases, but the rigorous theories seem to systemmatically underestimate the experimental p values. The reasons for this disagreement are discussed in addition to the general trends of the electrokinetic behaviour of Pyrex glass.