Interfacial Tensions of Polyelectrolyte Multiphase Coacervation

Interfacial tension is a crucial property for a charged polymer system undergoing liquid–liquid phase separation as it governs the structure and morphology of condensate phases. While the interface problem of simple two-phase coacervation has been well documented, little light has been shed so far on the multiphase separation process. In this study, we theoretically investigate the interfacial properties in multiphase coacervation driven by the asymmetry of the linear charge density for different polycations. We calculate the density profiles of all species at these interfaces as well as the variations of interfacial tensions with salt concentration. The results indicate that in a three-phase coacervation system, direct contact of the dilute phase with the most condensed phase is unstable, so a middle layer consisting of a less condensed phase must appear. Then, a core–shell structure is formed, which is independent of the presence or absence of salt ions. Our study is in good agreement with the previous literature and provides deeper insight into understanding the spatial structure of multiphase coacervates.