Multiphase Complex Coacervate Droplets from Two-Polyelectrolyte Systems

Microscale inhomogeneous polyelectrolyte complexes have been shown to form in coacervates from three or more polyelectrolyte components, as “protocells” with fatty acid, lipid, or protein adsorbed to the surface of a two-protein condensate droplet, or upon application of an electric field or a laser tweezer. Recently, we found that a transient internal microstructure can form in systems of only two polyelectrolytes via internal interfacial relaxation of aggregated complexes, and that this morphology is highly sensitive to the details of mixing and flow. Here, we report formation of protocell-like core-shell coacervates formed in a two-polyelectrolyte system, in cases of extreme non-stoichiometric mixing of the polyanion and polycation. We characterize where the transition from single to multiple emulsion coacervation occurs as a function of relative concentration of the two polyelectrolytes and salt, polyelectrolyte identity, and the mixing approach, and identify the compartmentalization of phases and chemical components of the multiple emulsion. We also discuss the metastability of the structures, and the possibility of using more complicated mixing protocols to form even more complicated structures using just two polyelectrolytes.