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Measurements have been made of the electrophoretic mobility and the stability of dispersions of two graphitized carbon blacks (Graphon and Sterling MTG) in aqueous solutions of sodium dodecyl sulphate, these carbons having similar adsorption properties but contrasting particle nature. Stability ratios for dispersions containing 0.1 M sodium chloride are compared with predictions of the Deryaguin-Landau-Verwey-Overbeek theory. There is good agreement between experimental and theoretical stability ratios for Graphon, indicating coagulation determined by a potential barrier.Rapid coagulation by Sterling MTG, even at high zeta potentials, is correlated with the secondary minimum. The experimental results suggest that both electrophoretic mobility and stability are determined by the radius of the primary particle rather than that of the total aggregate, as predicted theoretically when the electrical double layer is relatively thin.

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