Polymer Chemistry Effects on the Mechanics of Polyelectrolyte Complexes

Polyelectrolyte complexation is a phase separation phenomenon driven by the electrostatic interactions between two oppositely charged polyelectrolytes. Such materials are widely used in products like shampoo and are produced by organisms like sandcastle worms as bioadhesives. Processing polyelectrolyte complexes has the benefit of requiring only water as a solvent, avoiding the use of high temperatures or organic solvents. Additionally, their properties can be tuned by altering factors like the length, charge density and hydrophobicity of the polyelectrolyte. Furthermore, it is well understood that salt concentration strongly affects the mechanics of the polyelectrolyte complex. Adding salt typically causes swelling of the material, resulting in a softening of the complexes, in addition to disrupting the electrostatic interactions between the polyelectrolytes. However, the effect of the charged functional group of the polyelectrolytes on the mechanics of the materials is not well-understood. As such, we are interested in studying the effect of the charged functional group on the mechanics and its relationship with salt concentration. In particular, we are examining the linear viscoelasticity of polyelectrolyte complexes with carboxylate, sulfonate, phosphonate, and amine groups with different degrees of alkylation on polyelectrolyte complexes at different salt concentrations. These rheological studies give us insight into properties like viscosity and solid-to-liquid transitions in our material. Furthermore, we apply time-salt superposition to combine data from individual experiments and produce a master curve for each of the systems to allow for a broader examination of how the mechanical properties can be tuned with salt concentration – from glassy complexes at low salt to viscoelastic liquids at higher salt concentration. By understanding how salt concentration and polymer chemistry affect the linear viscoelasticity of polyelectrolyte complexes, we can design materials with desirable properties for applications ranging from adhesives to encapsulants, all while avoiding harsh polymer processing methods using high temperature and organic solvents.