Structure and Relaxation Dynamics for Complex Coacervate Hydrogels Formed by ABA Triblock Copolymers

Complex coacervate core hydrogels were formed by simply mixing two oppositely charged polyether-based ABA triblock copolyelectrolyte solutions, where A blocks functionalized with either ammonium or sulfonate moieties form micellar cores and the cores are bridged by B block, poly(ethylene oxide). Small-angle X-ray/neutron scattering revealed the detailed hydrogel structure, including the micellar core dimension and characteristics, and the midblock conformation as a function of polymer and salt concentration. Furthermore, the relaxation process of the hydrogels where the micellar cores are disordered between 8 and 9.5 wt% was investigated by dynamic mechanical measurement. We observed that the time-salt superposition principle equipped with a sticky Rouse model captures the hydrogel relaxation dynamics. Varying the charged block length produces a significant change in the relaxation time, which is mainly attributed to the fact that the chain pullout process from the micellar cores is hindered by the thermodynamic energy barrier. The tunable viscoelastic characteristics of the complex coacervate hydrogels have important implications for applications as injectable and self-healable materials.