Salt-concentration-dependent structure of Complex Coacervate Core Micelles

Complex coacervation is a liquid-liquid phase separation when two oppositely charged polyelectrolytes are mixed in an aqueous solution. Because of the nature of electrostatic interaction, the coacervates are highly responsive to solution condition such as ionic strength. In this study, complex coacervate core micelles (C3Ms) are formed by simple mixing of AB and A’B diblock copolyelectrolyte solutions in an aqueous solution where A and A’ are oppositely charged blocks, and B is PEO block. Since the cores are coacervates, the C3Ms are also highly responsive to salt concentration. We investigate the salt-concentration-dependent structure of C3Ms with various molecular weight of charged block using dynamic light scattering (DLS) and small-angle X-ray/Neutron scattering (SAX/NS). As salt concentration increases, the aggregation number and core radii of C3M decrease. This reflects that the interfacial area per chain increases due to reduced interfacial tension between cores and solvent at higher salt concentration. In addition, salt resistance of C3Ms becomes stronger as the molecular weight is larger.