Self-Assembly, Structure and Rheology of Polyelectrolyte Complex Hydrogels

Polyelectrolyte complexes (PEC) form when oppositely charged polyelectrolyte chains spontaneously associate and phase separate in aqueous media. Combining one or both polyelectrolyte chains with a neutral polymer restricts bulk phase separation of the PECs, and thus leads to self-assembled structures with PEC domains surrounded by neutral polymer coronae, forming micelles and hydrogels. The PEC domains in these assemblies can encapsulate therapeutics as well as genetic materials and thus have tremendous potential in drug delivery and tissue engineering applications.

We will present insights on the equilibrium structure and bulk properties of PEC hydrogel assemblages comprising oppositely charged block copolyelectrolytes. Detailed investigations of structure-property relationships of hydrogels comprising model block copolyelectrolytes with oppositely charged functionalized polyallyl glycidyl ethers as ionic and polyethylene glycol as neutral blocks will be discussed. Large-scale ordering of the nanoscale PEC domains is observed at high polymer loadings, characterized by a disorder-order transition followed by morphological transitions with increasing polymer loading. Complementary X-­ray and neutron scattering investigations providing a comprehensive structural description of these materials will be presented, strongly supporting our hypothesis on the charged block playing a structure-defining role and the neutral block undertaking a structure-directing role. The effect of key parameters such as polymer block lengths and concentration on the relationship between the nanoscale PEC morphology and equilibrium material properties, elucidated via detailed structure characterization and rheology studies, will also be discussed.