(569g) Polyelectrolyte Complex Hydrogels: Self-Assembly, Structure and Rheology

Polyelectrolyte complexes (PEC) form when oppositely charged polyelectrolyte chains spontaneously associate and phase separate in aqueous media. Combining one or both of the polyelectrolytes 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 of such PEC hydrogel assemblies comprising oppositely charged block copolyelectrolytes. Initial motivation will be provided by a brief discussion of structure and rheology of block copolypeptide hydrogels. It will be followed by 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. 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 and strongly supporting our hypothesis on the charged block playing a structure-defining role and the neutral block undertaking a structure-directing role will be presented. In addition, the effect of key parameters such as polymer block lengths and salt concentration on the equilibrium materials properties, elucidated via detailed structure characterization and rheology studies, will also be discussed.