Electrophoretic mobility of interacting colloidal spheres

Abstract

The electrophoretic mobility of charged colloidal spheres suspended in deionized water was measured as a function of the packing fraction ⌽ increasing from about 10 Ϫ6 to 2ϫ10 Ϫ3 . With increasing packing fraction, the mobility first increases linearly with the logarithm of the packing fraction and then saturates at a high value unaffected by the freezing transition. The electrostatic potential ⌿(r) was calculated numerically by solving the nonlinearized Poisson-Boltzmann equation in a cell model under conditions of charge regulation. The potential first is constant at low packing fraction and then decreases roughly linearly with log(⌽). In both cases the qualitative change in packing fraction dependence occurs once a significantly ͑typically 10-20 %͒ increases above 0 a given by the residual small ion concentration. Qualitatively similar behavior was found for particles of different size and surface chemistry and also under conditions of added salt. None of the theoretical approaches presently available is able to capture this interesting and complex behavior observed under low salt conditions.

Independent ion migration in suspensions of strongly interacting charged colloidal spheres

“…FEP(PFOA)78 and PS(SDS)102 were extensively dialysed against destilled and decarbonized water with IEX added to the reservoir All further sample preparation and the measurements were performed in a closed system including the measuring cells and the preparational units. Details of the continuous deionization procedures have been given elsewhere [30,31]. Since preparation may have severe influence on electrokinetic measurements, we nevertheless here give a short outline of the preparation set-up.…”

An Experimental Test of the Ion Condensation Theory for Spherical Colloidal Particles

“…But, frequently, the value of surface charge is determined on the basis of a Poisson-Boltzmann theory by fitting it to experimental measurements. These data are obtained from (i) experiments which probe the electrostatic interaction between particles (1-5) (such as static light scattering, video-microscopy, freezing line); and (ii) experiments in which a transport property is measured, for instance, conductivity (6) or electrophoretic mobility. Anyhow, this effective charge (as opposed to the titrable charge) is found to be considerably smaller in most cases (particularly in suspensions at very low ionic strength).…”

Enhanced structural correlations accelerate diffusion in charge-stabilized colloidal suspensions

“…We note that the effective charges of the DLVO interaction potential are generally found to depend on the determination method (see, e.g., Ref. [10]) and do not necessarily agree.…”

“…To be specific, φ and c s can be precisely determined by measuring the suspension's low-frequency conductivity [10]. The conductivity can be reproducibly adjusted in a closed tubing system -6 -between the minimum value, given by the self-dissociation of water plus the dissociation of the particle charges, and the maximum value set by aggregation of the particles due to the complete screening of the electrostatic repulsion.…”

“…The mixture was left to stand several days with occasional stirring. This stock suspension was filtered using 5 µm pore size filters and subsequently filled into a closed tubing system with a peristaltic pump, where the conductivity of the suspension can be controlled by the resin, through which the suspension is pumped or bypassed [10]. We use the minimal conductivity as a measure for the particle concentration in the circuit.…”