Multiphase Coacervation of Polyelectrolytes Driven by Asymmetry of Charged Sequence

The complex coacervation of oppositely charged polyelectrolytes is an important issue, which is relevant to many biological and industrial applications. While various biomolecules have been observed to form hierarchical multiphase structures in cells, its mechanism is still not fully understood. Here, we theoretically study the complex coacervation between the polyanion C and polycations A and B in solution and focus on the influence of charge sequence along the polyions on the multiphase coacervation. The electrostatic free energy is calculated with random phase approximation, and the phase diagrams are constructed by using the convex hull algorithm. It is revealed that the large asymmetry of charge patterns between A and B chains may induce the multiphase separation, driving the formation of two condensed phases, AC coacervate and BC coacervate, coexisting with a dilute phase. On the basis of our result, we propose a good criterion to determine if multiphase separation occurs or not. Furthermore, we analyze the effect of charge sequence of polyanion C as well as the addition of salt on the multiphase coacervation. This work provides insights into the underlying physics of sequence-dependent electrostatic interactions and the design of complex coacervates of polyelectrolyte mixtures.