Direct observation of charge inversion by multivalent ions as a universal electrostatic phenomenon

The study directly observed reversal of the polarity of charged surfaces in water upon the addition of trivalent and quadrivalent ions using atomic force microscopy. The charge inversion depends on the chemical composition, surface structure, size and lipophilicity of the ions and were sensitive to their valence. The study measures the force between two oppositely charged surface and its dependence on the properties of the screening ions. It was observed that the in the presence of a sufficiently high concentration of travalent and quadrivalent ions, the force reversibly changes signs.