Exploring charge inversion in electrolyte mixtures of trivalent and monovalent ions

At room temperature ion-ion correlations and counterions volume effect play a crucial role in the description of the electrical double layer of colloidal particles. In fact, in many instances, the inclusion of the short range correlations between ions in the study of the ionic distribution and the consideration of the ion´s size lead to quite different results with respect to the classical treatment (where ions are assumed to be points). In particular, these discrepancies become more noticeable for highly charged particles in the presence of moderate or highly multivalent counterion concentrations. Moreover, it can be shown that the existence of an electrolyte mixture consisting of multi- and monovalent counterions may cause that system to become overcharged, a feature that cannot be predicted from a classical point of view based on the Boltzmann distribution function. In order to explore the charge inversion in electrolyte mixtures of trivalent and monovalent ions, the interaction of mica surfaces in two different concentrations of LaCl₃ before and after adding NaCl is investigated through the surface force apparatus(SFA) and these experimental results can demonstrate that the charge inversion is indeed enhanced by a monovalent salt.