Complexation in Asymmetric Solutions of Oppositely Charged Polyelectrolytes:  Phase Diagram

We propose a combination of the mean-field theory and the random phase approximation to describe complexation in solutions of oppositely charged polyelectrolytes with the asymmetric content of positively and negatively charged chains. The phase diagram of the system is calculated. We show that “excess” polyions coexisting with small neutral complexes (each complex consists of one polycation and one polyanion) at very small polymer concentrations can first aggregate into big spherical clusters with the following formation of cylindrical and lamellar structures at the increase of polymer concentration. All clusters formed have nonzero net charge due to the charge asymmetry of the solution. The physical reason for the stability of the clusters (complexes) is discussed.