Phase Diagrams of Salt-Free Polyelectrolyte Semidilute Solutions

We analyze the phase behavior of polyelectrolyte salt-free solutions using the random phase approximation (RPA). Within this approximation, the phase diagrams of salt-free polyelectrolyte solutions show phase separation even without including short-range attractions or ion condensation. We find that the phase behavior of large chains resembles the phase diagram of polymer network solutions. That is, the equilibrium is established between a swollen network phase and a chain-free phase. Even though RPA is capable of reproducing certain aspects of the phase diagram, the model has to be modified to include ion condensation self-consistently in the analysis.