Stability of non-aqueous dispersions. Part 3—Rate of coagulation of sterling MTG in aerosol OT + n-heptane solutions

Abstract

Measurements of electrophoretic mobility and of rate of coagulation have been made for dispersions of a graphitized carbon black (Sterling MTG) in solutions of Aerosol OT (sodium di-2-ethylhexyl sulphosuccinate) in n-heptane for a range of surfactant concentrations. Curves of theoretical ratio stability, as a function of the effective Hamaker constant, against zeta potential were constructed. Comparison of the experimental results with these curves shows that the Derjaguin-Landau-Overbeek theory predicts the correct order of magnitude for the stability ratios. However, to account for the relationship between experimental stability ratio and zeta potential in terms of the theory it is necessary to assume values of the Hamaker constant varying over two orders of magnitude, which is improbable and suggests that the theory would be susceptible to further refinement.