Computer simulations of a polyelectrolyte chain with a mixture of multivalent salts

Diluted solutions of a single, electrically charged polymer chain, its monovalent counterions and two kinds of multivalent salts are investigated. In particular, the influence of the salt concentrations and valences on the mean effective charge per monomer, total inner energy, radius of gyration and various pair correlation functions of the monomers and free ions are analysed. The calculations show that it is the four-valent and three-valent ions, oppositely charged to the monomers, that mostly occupy the space around the polymer and tremendously increase their number there compared to that in the bulk. Furthermore, reductions in the polymer size and effective charge per monomer appear, especially for increasing amount of the four-valent salt. Thus, there is an evidence for polymer conformational changes associated with the ion condensation onto the chain.