Effect of charge density and sequence on physical properties of salt-free polyelectrolyte solutions

Polyelectrolytes are polymers with ionizable monomers. Due to the electrostatic interactions, polyelectrolytes exhibit weaker scalings compared to neutral polymers for viscosity, diffusion coefficient, and frequency responses, showing potential in viscosity modifiers and small ion transport applications. However, we still lack a full understanding on the role of charge fraction and charge sequence on salt-free solution behavior. At concentrated regime, the mechanism by which entanglements happen in polyelectrolytes is of importance as strong electrostatic interactions dominate and delay the entanglement compared to neutral polymers of the same length, suggesting polyelectrolytes as potential candidates for soft materials. Aided by random and block copolymers with varying charge fractions (20-80%) and types, we will enrich our understanding of the electrostatic interactions and the resulting conformational changes. PDMAEA and PAA are utilized as cationic and anionic monomers, respectively, and PBA consists the neutral part. The effect of each interaction will be explored by steady shear viscosity and frequency sweep measurements, and resulting changes in relaxation time, critical overlap concentration c*, entanglement concentration Ce and modulus Ge, will be further discussed.