Scattering Investigations of Structure and Dynamics of Triblock Polyelectrolyte Complex Hydrogels

Polyelectrolyte complex (PEC) hydrogels are physically crosslinked 3-D networks that form upon complexation between oppositely charged polyelectrolytes. The development and use of PEC hydrogels for diverse biomedical applications require an in-depth understanding of the thermodynamics and kinetics of hydrogel assembly as well as their mesoscale structures and bulk properties. In this talk, we introduce the intimate correlations between PEC domain morphologies and material relaxation timescales in hydrogels comprising oppositely charged ABA triblock polyelectrolytes. Polymer size and concentration as well as solution ionic strength were all found to dictate the PEC domain morphologies, size and arrangements. X-ray photon correlation spectroscopy (XPCS) investigations revealed two distinct relaxation modes of the nanoscale PEC domains. The polymer concentration-independent faster relaxation was expected to capture the dynamic processes inside the PEC domains, while the slower polymer concentration-dependent domain relaxation timescales were found to be inherently linked with the equilibrium hydrogel structure. Upon addition of salt, both relaxation modes became faster, indicating speeding of the intra-domain relaxations and smaller, faster-relaxing PEC domains.