Phase transitions in solutions of semiflexible polyelectrolytes

Using a mean-field model, we have studied the phase behavior of a collection of semiflexible polyelectrolytes with electrostatic and anisotropic excluded volume interactions. The interference between the second-order critical phenomenon in the flexible limit and the first-order isotropic-nematic phase transition in the rod limit is found to be richly dependent on the intrinsic chain stiffness, polymer concentration, salt concentration, and temperature through the Flory-Huggins chi parameter. For intrinsic chain stiffness below a critical value, there exists only a critical point and a coexistence curve between two isotropic phases. For smaller values of stiffness, but above the critical value, we have found a triple point corresponding to the coexistence of two isotropic phases and one anisotropic phase. As the chain stiffness is increased progressively, the triple point moves towards lower polyelectrolyte concentration and approaches the critical point. If the chain stiffness is increased even more, another triple point emerges corresponding the coexistence of one isotropic phase and two anisotropic phases. (C) 2002 American Institute of Physics.