Polymer chemistry and effect on the linear viscoelasticity on polyelectrolyte complexes

Polyelectrolyte complexes are formed through the electrostatic interaction of oppositely charged polymers. Depending the identity of salt, polyelectrolyte complexes can result in both solid precipitates and/or a liquid-liquid phase separation known as complex coacervation. The material properties can also change based on variations in the polymer chemistry, and the complex interplay between electrostatic interactions and water structure, controlled by salt. We tested three different polymer systems over a range of polymer chain lengths and salt conditions to understand how variations in polymer chemistry affect the thermodynamic phase behavior and the resulting material dynamics. The linear viscoelasticity of each polymer system was investigated under different salt conditions to enable a time-salt superposition and facilitate a broader characterization of the stress relaxation behavior. We compare differences in the slope of the horizontal shift factors as a function of salt concentration, which can be related to the activation energy barrier for the rearrangement of ionic interactions between polymers. The goal of this systematic study is to establish a general understanding of how molecular-level parameters can be used to tune the phase behavior and viscoelastic properties.