Molecular Exchange Kinetics in Complex Coacervate Core Micelles:Role of Associative Interaction

Complex coacervate core micelles (C3Ms) have been investigated in a wide range of applications owing to stimuli-responsiveness and hydrophilic cores. Compared to structure and morphology, much less is known about the kinetics of C3Ms, yet the fundamental understanding is essential for micelle stability, reproducibility, and structure design. In this study, we investigated the equilibrium exchange dynamics between C3Ms characterized by time-resolved small-angle neutron scattering (TR-SANS) measurement. A pair of well-defined poly(ethylene oxide-b-allyl glycidyl ether) (PEO-PAGE) was synthesized and functionalized with charged moieties including guanidinium (G), ammonium (A), and sulfonate (S); one with a normal PEO, and the other with a fully deuterated PEO. C3Ms with hydrogen/deuterium labeling were prepared by simple mixing of two oppositely charged hPEO-PAGE or dPEO-PAGE solutions, respectively. Strong dependence of the exchange rates on the salt and ion pair revealed that the coacervate core dynamics is crucial. Proposed relaxation model with sticky-Rouse dynamics and thermodynamic barrier for chain expulsion captures the relaxation behavior of C3Ms.