Effect of the surface conductance on electrokinetic potential calculated from electrophoretic mobilities of the diamond particles in ethanol electrolyte solutions

Effect of the surface conductance on the ζ-potential of synthetic diamond particles (with sizes of 0.5–1 μm) determined from their electrophoretic mobility in ethanol solutions of 1:1 electrolytes over the range C=10−5–10−2 M was studied. The conductivity of dilute diamond suspensions at the variable particle volume fraction was measured and the dependencies of surface conductivity (Ks) on the electrolyte concentration were calculated by expression of the Wagner theory. It was found that Ks has excessively high values, continually increasing with the growth of C and having high non-zero values at the points of a reversal of ζ-potential sign to positive, found at C=5×10−4 M CsBr and C=10−2 M NaClO4. Such character of the dependency Ks (log C) is explained by the preferable specific adsorption of cations and the main contribution of Stern layer to the surface conductance. It was found that the plots ζ (log C), derived using Smoluchowskiʹs equation, show a weak dependencies on C in the whole concentration range and disconcerting maxima. Incorporation of the experimental Ks values in the Henryʹs equation brings to a linear character of the corresponding plots ζ (log C) with the slope 20–25 mV per decade.