Phase behaviors of a weakly charged stoichiometric polyanion/polycation blend with asymmetry in chain sizes and van der Waals interactions

A study on the phase behaviors of a salt-free stoichiometric blend from weakly charged polyanions and polycations has been performed. A free energy functional for the blend is formulated as the sum of Gaussian contribution and effective interaction terms, whose local part is given by the excess equation of state for the blend and nonlocal part through Coulomb interactions. Then, the Landau free energy expansion is obtained as a series in component density fluctuations. Using the Landau energy, the blends with asymmetry in chain sizes and van der Waals interactions are probed at various charge fractions to analyze their nanoscopic phase separation due to global electroneutrality. The location of continuous transition and mesophase formation not only upon cooling but also upon heating are deeply investigated. In addition, the control of the equilibration of mesophases through pressurization is discussed in the viewpoint of designing stimuli-responsive structural materials from the polyelectrolyte blends.