Unraveling the Temperature-Dependent Relaxation Dynamics of Ionic Liquid-Plasticized Compleximers

Polyelectrolytes with ionic domains screened by bulky hydrophobic segments form processable, hydrophobic complexes called “compleximers”. Ionic liquids, which are chemically similar, further plasticize compleximers, yet the mechanisms behind their plasticization effects and distribution within the complexes remain unclear. This study examines the relaxation dynamics of plasticized compleximers across multiple length scales using rheology, fluorescence recovery after photobleaching (FRAP), and broadband dielectric spectroscopy (BDS). The incorporation of ionic liquids into compleximers reduces their glass transition temperature (T_g), accelerates diffusive processes, increases segmental motion, and leads to a small decrease in activation energy associated with these relaxation processes. However, the activation energies vary substantially between techniques, probing different physical processes: approximately 200 kJ/mol in rheology, 50 kJ/mol in FRAP, and 90 kJ/mol in BDS. These variations suggest that collective dynamics strongly influence the compleximer rheology, making the mobilization (and activation) of polymer chains distinct from the local movement of ionic segments.