Relaxation Dynamics in Complex Coacervate Hydrogels Formed by ABA Triblock Copolymers

Incorporation of complex coacervate domains as physical crosslinks in polymer network leads to multi-responsive hydrogels with versatile functionalities. We investigate the relaxation dynamics of the hydrogels as a function of salt concentration, accompanied by the structural characterizations. Using the hydrogels constructed by mixing oppositely charged ABA triblock copolymers of equal block lengths in aqueous media, we observed that the dynamic moduli spectra are well superposed with varying salt concentration by the time-salt superposition (TSS). The successful superposition indicates the rheological simplicity of coacervate hydrogels and allows a deeper understanding of the hydrogel rheology within the framework of polyelectrolyte chain exchanges. Based on a model combining the sticky Rouse-like diffusion in coacervate phase and the activated chain pull-out from the coacervate core, we rationalize the observed dependencies of relaxation dynamics on the length and ionic group of charged end block as well as the salt concentration. The results will be discussed in conjunction with the current understanding of the polyelectrolyte complexes and the practical implications such as the injectability and self-healing in hydrogels.