ABSTRACT
From a theoretical point of view, the PM can be introduced in the theoretical description of the EDL by means of the integral equation formalism [13]. In fact, the so-called hypernetted-chain/ mean-spherical approximation (HNC/MSA) began to show the de ciencies of the classical EDL model more than two decades ago, claiming since then that the PB approach is inadequate for solutions with multivalent counterions [15,16]. In particular, under conditions propitious for charge inversion (i.e., high particle surface charge densities or/and electrolyte concentrations), the ion concentration pro les calculated with the HNC/MSA exhibit an oscillatory behavior and unexpected changes in the sign of the electrostatic potential. Conversely, monotonic functions (with respect to the distance from the surface plane) are obtained for the ion concentration pro les and the electrostatic potential by using the classical EDL model [2,17]. Although similar conclusions have been reported by using computer simulations as well as other theoretical approximations, only in recent times the PM models have started to be compared with experimental data [17-23]. Accordingly, the main purpose of this work is to study the experimental charge inversion of latex particles by means of electrophoretic mobility measurements. Moreover, the experimental results will be compared with predictions obtained with the GC model as well as HNC/MSA in order to analyze the effect of the ionic size correlations for this kind of experiments. To this end, we will rst study the effect of different multivalent electrolytes on the latex particles. Afterwards, we will look into mixtures of mono-and multivalent electrolytes on the same system. The objective is therefore to draw up the boundaries of the charge inversion for a colloidal model system by putting emphasis on the importance of size correlations in the description of the colloidal EDL.
