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. Complex coacervation is an entropically driven, associative liquid-liquid phase separation that results in a polymer-rich coacervate, and a polymer-poor supernatant dissolved in an aqueous solution. Salt-driven plasticization allows for the use of complex coacervation as a processing strategy. However, it is not clear whether many of the design rules associated with traditional polymers will still hold 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 and hydrophobicity. We characterized the resulting solid PEC materials using dynamic mechanical analysis and tensile tests. Our data show that the mechanics, which range from brittle to ductile, are intrinsically tied to PEC water content. We also highlight the effect of temperature, humidity, and salt concentration on the glass transitions of these materials to show how we can use these parameters to process PEC materials and achieve different mechanical responses.