Influence of salt on the structure of polyelectrolyte solutions: An integral equation theory approach

We investigate the influence of monovalent saltions on the structural properties of polyelectrolyte solutions using an integral equation theory. In this approach all species of the solution (polyions, counterions, and positively and negatively charged saltions) are treated explicitly leading to a four-component system. The polymer-reference-interaction-site model for this system, together with the reference-Laria-Wu-Chandler closure is solved numerically. We demonstrate that addition of salt leads to a screening of the Coulomb interaction, which is well captured by the Debye-Huckel potential with a salt density-dependent screening length, by discussing various correlation functions. Furthermore, we show that for an appropriate range of parameters, such as density or Bjerrum length, a shell of equally charged saltions exists in the vicinity of the polyion. The effective potential between two monomers reflects attraction among the equally charged polyions with a pronounced dependence on the salt concentration. (C) 2003 American Institute of Physics.