ABSTRACT
Charge inversion occurs when the effective charge of a surface exposed to solution reverses polarity due to an excess of counterions accumulating in the immediate vicinity of the surface. Using atomic force spectroscopy, we have directly measured the effect on charge inversion of changing the dielectric constant of the solvent and the surface-charge density. Both decreasing the dielectric constant and increasing the bare surface-charge density lower the charge-inversion concentration. These observations are consistent with the theoretical proposal that spatial correlations between ions are the dominant driving mechanism for charge inversion.
ABSTRACT
We have directly observed reversal of the polarity of charged surfaces in water upon the addition of trivalent and quadrivalent ions using atomic force microscopy. The bulk concentration of multivalent ions at which charge inversion reversibly occurs depends only very weakly on the chemical composition, surface structure, size, and lipophilicity of the ions, but is very sensitive to their valence. These results support the theoretical proposal that spatial correlations between ions are the driving mechanism behind charge inversion.
