Theory of Phase Behavior of Weakly Charged Polyelectrolytes

Abstract

<p>A self-consistent field theory is developed for weakly charged polymeric systems composed of charged-neutral diblock copolymers and homopolymers. This generic model can be used to describe the phase behavior of a number of different charged polymeric systems, including charged polymer/homopolymer blends and ionic liquid/homopolymer mixtures. It is found that the miscibility of the system is increased by the increase of the charge fraction and the anion volume. Random phase approximation has also been used to calculate the spinodal lines for polyelectrolyte/homopolymer blends and polyelectrolyte solutions. Both systems exhibit micro- and macro- phase separated regions. It is also shown that an increase of the charge fraction stabilizes the homogeneous phase over the inhomogeneous ones and a decrease of the Bjerrum length stabilizes the microphase separated state over the macrophase separated state. Finally, the reciprocal-space method is used to solve the self-consistent field equations for the polyelectrolyte/homopolymer blends. Full phase diagrams showing microphase separated structures of lamellae, hexogonal and body-centered cubic lattice, as well as 2-phase region of coexistence of lamellae and homogeneous are obtained.</p>