(403g) Modeling the Complexation of Homologous Polyelectrolytes

Complexation of polyelectrolyte is caused a well-known demixing instability originating from sufficiently strong electrostatic correlation. The quantitative modeling of this instability is challenging because it is sensitive to a variety of short-ranged features including monomeric polarity, molecular flexibility, and charge pattern. With the recent advancements in theoretical modeling, capturing such features has become possible. To put the theory into tests, we designed experiments using polycation and polyanion with identical backbone, and with viariable polarity and mixing stoichiometry. Aided with dual-fluorescent labeling and elemental mapping, we determined the phase diagrams and revealed a hitherto unexpected reentrant behavior in strongly non-stoichiometric solutions, and found favorable agreements with the theoretical predictions. In particular, we rationalize the emergence of the reentrant window, in which adding salts causes the polymers to salt out, by considering the balance of the mixing entropy of the neutralizing counter-ions and the strength of electrostatic correlation. The application of our model to other recent experimental studies is also presented.