Debye length in multivalent electrolyte solutions

We present the results of direct force measurements between charged surfaces in solutions of multivalent electrolytes (MgSO4, K4Fe(CN)(6), and Th(NO3)(4)). For surface separations greater than approximately 3 nm the measured forces between the surfaces agree, within experimental uncertainty, with the predictions of the Derjaguin-Landau-Verwey-Overbeek theory of colloidal interactions. In particular, we find that various proposed corrections to the electrostatic screening lengths in solutions of multivalent electrolytes are either invalid or beyond the limits of measurement by present techniques.