FIG. 7.

Examples of polyvalent ions adsorbed onto a charged particle and reversing its effective charge (a), and of specific adsorption of ions of the same charge as the particle, contributing to an effective increase of the effective charge (b). These are the two cases when the surface charge cannot be readily estimated from ζ potential—the presence of polyvalent ions (a) and specific adsorption that transcends the electrostatic repulsion (b). Reprinted from Shaw^[28] (this article was published in Introduction to Colloid and Surface Chemistry, D. J. Shaw, © Elsevier [2003]).