Charged surfaces submerged in an electrolyte solution can sometimes become oppositely charged. This nonintuitive phenomenon, known as charge inversion, happens when excess counter ions adsorb, or adhere, to the surface. It can occur in a number of chemical and biological settings. In certain situations, theory predicts that a highly charged surface not only changes sign, but can become more highly charged than the original surface. This is known as giant charge reversal, but remains controversial and has never been observed experimentally.
Results reported this week in the Journal of Chemical Physics confirm, for the first time, giant charge reversal for a surface in contact with a trivalent electrolyte solution. In contrast to previous observations, this did not require a highly charged surface.
The investigators, Zhi-Yong Wang of Chongqing University of Technology in China, and Jianzhong Wu of the University of California, Riverside, found that the dielectric response of the solvent enhances correlation of multivalent ions with oppositely charged surface groups. This facilitates formation of interfacial couplings of opposite charges called Bjerrum pairs, and leads to the observed giant charge reversal.