Robust and Tough Wet Adhesives based on Polyelectrolyte Complex Hydrogels

Significant advances in emulating natural glues have led to a diversity of wet adhesive chemistries. However, most current adhesives cure slowly in unprotected aqueous environments, leading to precursor deactivation, dilution, and weak adhesion. In this talk, I will discuss our progress in developing robust wet adhesives based on polyelectrolyte complex-interpenetrating network (PEC-IPN) hydrogels. These hydrogels are fabricated by curing polymeric adhesive precursors in protected environments provided by self-assembled polyelectrolyte complex (PEC) hydrogels, thus mitigating precursor dilution. In the resulting PEC-IPN hydrogels, the PEC network also features a mesoscale hierarchical structure, contributing to the adhesives' superior mechanical and adhesive performance. Model PEC-IPN hydrogels comprising a PEC network composed of oppositely charged block polyelectrolytes and a covalently crosslinked tetra-PEG network will be demonstrated to serve as a material platform for robust and tough wet adhesives. X-ray scattering investigations will establish the persistence of the PEC network upon the inclusion of tetra-PEG chains in it and their subsequent photocrosslinking. Simultaneously, marked improvements in shear and tensile strengths of PEC-IPN hydrogels upon incorporating the covalent tetra-PEG network, even as a minor component, will be demonstrated. Precise tuning of microstructure and shear moduli of the hydrogels prior to the formation of covalent networks, and of the shear and tensile strength, toughness, and swelling characteristic in the IPN hydrogels will be highlighted.