EFFECTIVE FORCES BETWEEN MACROIONS - THE CASES OF ASYMMETRIC MACROIONS AND ADDED SALT

The distance-resolved effective forces between two spherical, highly c harged colloidal macroions are calculated by computer simulation withi n the primitive model of strongly asymmetric electrolytes. In particul ar we consider the case of two asymmetric macroions, i.e., two particl es with different charges and different radii, as well as the case of added salt ions. Different parameter sets corresponding to typical exp erimental samples an investigated. The results are compared with the p redictions of traditional linear screening theory of Derjaguin and Lan dau [Acta Physicochim. URSS 14, 633 (1941)] and of Verwey and Overbeek [Theory of the Stability of Lyophobic Colloids (Elsevier, Amsterdam, 1948)]. For moderate charge asymmetries we find a semiquantitative agr eement and verify different scaling laws obtained from Derjaguin-Landa u-Verwey-Overbeek (DLVO) theory justifying the DLVO description of bin ary mixtures and of charge- and size-polydisperse macroion samples. Ho wever for very large asymmetry, particularly for the mixture of charge d and uncharged colloid particles, we obtain a nonzero repulsive inter action contrarily to DLVO theory.