Charge Stabilization and Dynamics in Polyelectrolyte Phase Separation

The phase separation of polyelectrolytes like proteins and RNAs underlies the formation of biomolecular condensates that serve a variety of cellular functions. These condensates can exhibit a distribution of sizes that determines their mass transfer properties for biochemical processes, yet the mechanisms of size control are not well understood. Here, we investigate the role of polymer charge in the phase separation dynamics and stabilization of a polyelectrolyte condensate in a solution containing dissolved salt ions. Employing a continuum theory that captures the interfaces between phases as well as electrostatic interactions, we study the dynamics of patterns that emerge during spinodal decomposition. We identify scaling relationships between key polymeric and solution parameters that determine the degree of charge stabilization, including defining a region of finite wavelength instability for polyelectrolyte solutions. The mechanism of charge stabilization may be relevant generically for biopolymers undergoing phase separation which possess non-negligible net charge under physiological conditions, independent of the origin of the interactions that drive phase separation.