PRECIPITATION OF HIGHLY-CHARGED POLYELECTROLYTE SOLUTIONS IN THE PRESENCE OF MULTIVALENT SALTS

Solutions of highly charged polyelectrolyte chains are described by a model that introduces ion condensation as a random charge along the po lymer. The degree of condensation is obtained by solving the Poisson-B oltzmann equation with cylindrical geometry. Short range electrostatic attractions between the monomers via the condensed counterions of hig h enough valency lead to reversible chain precipitation. The range of polymer concentration over which salt-free solutions are unstable is d etermined, as well as the miscibility of the chains when salt is added . Redissolution at high salt concentration is due to a screening of th e short range electrostatic attractions. Precipitation of chains in mi xtures of movalent and multivalent salts is also studied. We find the range of salt concentration where chains precipitate. The model explai ns the experimental results on the precipitation of sodium and lanthan um polystyrene sulfonate solutions in presence of multivalent salts [L aCl3 and Th(NO3)(4)]. (C) 1995 American Institute of Physics.