Effects of surface conduction on the electrokinetic properties of colloids

Abstract

To quantify the effects of surface conduction behind the slip plane on the electrokinetic transport properties of colloids, we have extended the thin-double-layer theory of Fixman for dilute sols of spherical particles. The computations show that it causes the static conductivity and the low-frequency dielectric response of the sol to increase and the mobility of the particles to decrease. Hence, the occurrence of surface conduction significantly changes the relationships between the different electrokinetic properties. Therefore, for a rigorous interpretation of experimental results taking possible effects of surface conduction adequately into account, it is imperative to collect data with more than one electrokinetic technique. For polystyrene latices, a comparison between theory and experiment has been made. The mobility and static conductivity data can be well reconciled if surface conduction is accounted for. The corresponding estimates of surface charge densities agree very well with values obtained by independent measurements. However, the extreme dielectric behaviour of latex colloids cannot be attributed to surface conduction.

Electrokinetics of Concentrated Suspensions of Spherical Colloidal Particles with Surface Conductance, Arbitrary Zeta Potential, and Double-Layer Thickness in Static Electric Fields

“…The drag coefficient λ i is related to the limiting conductance 0 i of the ith ionic species by (2) [9] where N A is Avogadro's number. At equilibrium, that is, in the absence of the electric field, the distribution of electrolyte ions obeys the Boltzmann distribution [10] and the equilibrium electric potential (0) satisfies the PoissonBoltzmann equation [12] ρ (0) el being the equilibrium electric charge density.…”

“…They analyzed the role of different Stern-layer adsorption isotherms on both electrophoretic mobility and suspension conductivity. More recently, Kijlstra et al (12) applied the theory of Stern layer transport to the study of the low-frequency dielectric response of colloidal suspensions, extending the thin double-layer theory of Fixman (3, 7). Likewise, Rosen et al (13) generalized the standard theory of the conductivity and dielectric response of a colloidal suspension in AC fields of DeLacey and White (5), assuming the model of Stern layer developed by Zukoski and Saville.…”

“…suspensions (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). However, in a great number of practical situations, suspensions are usually more concentrated than those typically considered as dilute, so some theoretical approaches to the issue of concentrated suspensions, including electrophoresis (16), sedimentation (17,18), electrical conductivity (19), and electroacoustic phenomena (20)(21)(22), to mention just a few, have been published in the past few decades.…”

The electrokinetic properties of latex particles: comparison of electrophoresis and dielectrophoresis

“…Both the AC and DC electrical properties of micrometre and submicrometre latex particles have been investigated by many research groups, using techniques such as electrophoresis, electrical conductivity measurements, electroacoustics and dielectric spectroscopy; see, for example, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…In this model the shear plane was located some way into the diffuse layers so that the ions contributing to the surface conductance effectively move in the diffuse layer with a high mobility. Other authors [7,8,12] introduced the concept of a surface conduction arising from charge movement in the region behind the slip plane. This conductance contains two components, one due to convection of ions due to electric field-driven movement of the liquid (electroosmosis) and another due to the movement of the ions directly from the action of the electric field on the charge, the conduction current.…”