Effects of Charge Asymmetry on Condensate Coarsening

Biomolecular condensates are membraneless compartments that concentrate a set of macromolecules and are proposed to form via phase-separation. Species that are enriched within condensates commonly include charged biopolymers that can have a high degree of charge asymmetry (i.e., RNA and DNA versus proteins). While condensate formation is driven by short-range attraction between constituent molecules, net charges can mediate long-ranged repulsion. Using molecular dynamics simulations and an equilibrium field theory, we show that such opposing interactions can suppress coarsening so that many droplets of equal size coexist at equilibrium. This size control depends strongly on the charge asymmetry between constituents and the interfacial energies of the droplets, while the strength of the short-ranged attractions has a weak influence. Our work reveals how electrostatic effects control droplet size, which is relevant for understanding biomolecular condensates and creating synthetic patterns in chemical engineering.