(272i) Design Rules and Mechanical Properties of Polyelectrolyte Complex Materials.

The formulation of functional polymers, like adhesives and coatings, is particularly challenging due to the interplay between performance and processability requirements. Polyelectrolyte complexation is an entropically driven, associative phase separation that results in a polymer-rich coacervate, and a polymer-poor supernatant dissolved in an aqueous solution. Polyelectrolyte complexation can be used in the self-assembly of a wide range of responsive, bioinspired materials ranging from dehydrated thin films, fibers, and bulk solids to dense, polymer-rich liquid complex coacervates. Salt-driven plasticization allows for the use of polyelectrolyte complexation as an aqueous, polymer processing strategy. However, it is not clear whether many of the design rules associated with traditional polymers, such as molecular weight and glass transition temperature effects, will apply for materials based on polyelectrolyte complexation (PECs). To understand this design space, we tested a library of PECs made from oppositely-charged methacrylate copolymers of varying charge density, hydrophobicity, and chain length. We characterized the phase behavior and mechanical properties of the resulting liquid coacervates and solid PEC materials. Our data shows that copolymer chemistry can be used to tune the composition and subsequent viscoelasticity of both solid and liquid materials. Furthermore, the solid-state mechanics can range from brittle to ductile, and are intrinsically tied to the water content of the PEC, with copolymer chemistry affecting the amount of water uptaken at a given condition. Lastly, we also characterized the glass transitions of PECs and show that they are coupled to both water content and temperature, creating a glass transition line that can be modulated by tuning both environmental conditions and polymer chemistry.