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

Abstract

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 ( K s ) on the electrolyte concentration were calculated by expression of the Wagner theory. It was found that K s 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 NaClO 4 . Such character of the dependency K s (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 Smoluchowski's equation, show a weak dependencies on C in the whole concentration range and disconcerting maxima. Incorporation of the experimental K s values in the Henry's equation brings to a linear character of the corresponding plots ζ (log C ) with the slope 20–25 mV per decade.