  Forces between charged silica particles in solutions of multivalent coions
are measured with colloidal probe technique based on atomic force microscopy.
The concentration of 1:z electrolytes is systematically varied to understand
the behavior of electrostatic interactions and double-layer properties in these
systems. Although the coions are multivalent the Derjaguin, Landau, Verwey, and
Overbeek (DLVO) theory perfectly describes the measured force profiles. The
diffuse-layer potentials and regulation properties are extracted from the
forces profiles by using the DLVO theory. The dependencies of the diffuse-layer
potential and regulation parameter shift to lower concentration with increasing
coion valence when plotted as a function of concentration of 1:z salt.
Interestingly, these profiles collapse to a master curve if plotted as a
function of monovalent counterion concentration.
