Structural Evolution and Phase Behaviors of Electrostatic Macromolecular Assemblies

Macromolecular assemblies that are driven by electrostatic interaction create an avenue for a broad range of biomedical applications including therapeutic delivery and tissue engineering. These aqueous solution micellar assemblies are able to sequester hydrophilic nucleic acid macromolecules and release them upon a stimulus applied. Further, increasing the polymer concentration above micelle overlap concentration leads to unique hierarchical structures, e.g. body-centered cubic, and hexagonally packed cylinders morphologies, that can be strategically exploited as transient hydrogel networks with tunable topology, rheology, and electrical conductivity. The structural evolution and phase transition of micellar electrostatic assemblies, however, remains elusive. Herein, we systematically employ small-angle X-ray scattering and neutron scattering to investigate the structural evolution of micellar electrostatic assemblies, and the large-scale phase behaviors of concentrated micelles evolving into hierarchical hydrogels. We compare the kinetics and ordering processes between micelles composed of carefully synthesized homo-, di-, and tri-block charged polymers. These findings will assist the rational design of electrostatic macromolecular assemblies for future applications.