Correlations between macroions in mixtures of charged and uncharged macroparticles

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Abstract
Addition of uncharged or charged macroparticles to a solution of macroions and counterions significantly affects the macroion–macroion correlation function. This effect is studied using the hypernetted-chain integral equation. Two simple models are examined: (i) a multicomponent primitive model treats a solution as a mixture of charged and uncharged hard spheres, (ii) a one-component model where the electrostatic interactions are accounted for by the screened Coulomb potential and the effect of neutral macroparticles is given by an approximate ‘‘volume exclusion’’ potential. Both models ignore the molecular nature of solvent. The calculations presented here indicate that the one-component model is a poor representation of the actual interactions between macroions in the presence of the neutral macroparticles represented as hard spheres. In the second part of the work we study the mixtures of macroions (two positively charged macroions that differ in size) with a common counterion. The radial distribution functions are presented for systems containing mono- or divalent counterions for a range of macroion concentrations.