THE ROLE OF EFFECTIVE TRIPLET INTERACTIONS IN CHARGED COLLOIDAL SUSPENSIONS

The traditional theory of the effective interactions between charged c olloidal particles ('macro-ions') treats the screening of the counter- ions on a linear response level resulting in the well-known screened C oulomb pair potential proposed by Derjaguin, Landau, Verwey and Overbe ek. In general, however, due to non-linear counter-ion screening, the effective interactions involve many-body contributions. Using molecula r dynamics simulation of the highly asymmetric primitive model with th ree macro-ions, we calculate the effective triplet forces and compare them with the pairwise contributions. Near touching of a macro-ion tri pler, the triplet interaction represents a significant attractive corr ection to the repulsive pairwise interaction while it is small for lar ge inter-particle separations. Furthermore, we compare our simulation results for the triplet forces with an analytical expression gained fr om a density functional perturbation approach. Upon performing a suita ble renormalization, we find reasonable agreement for situations of we ak and strong coupling as well as for situations with added salt ions.