Local Segmental Dynamics of Polyelectrolyte in Complex Coacervates

Complex coacervates (CC) are polymer-rich liquid phase generated when two oppositely charged polyelectrolytes are mixed in aqueous solutions. Dynamics of CC has mostly been studied by rheology, probing relaxation times on multiple length scales such as reptation, entanglement and ion-pair rearrangement. However, there are still limited information on local segmental dynamics that correspond to angstrom-scale. In this study, the segmental dynamics of CC are revealed as a function of salt concentration by quasi-elastic neutron scattering (QENS). Model polyelectrolytes functionalized with ammonium, guanidinium and sulfonate groups were synthesized by anionic ring-opening polymerization and post-modification. QENS results show that the amount of unpaired segments in ammonium-based coacervates is increased and their segmental dynamics are enhanced with salt concentration. In stark contrast, guanidinium-based coacervates show slower segmental dynamics and their amount is independent of the salt concentration.