Effects of Chain Length Asymmetry and Salt Ion Valency on Polyelectrolyte Complexation

Polyelectrolyte (PE) complexation, driven by electrostatic interactions between oppositely charged macromolecules, is influenced by the nature of PEs (charge density, molecular weight, chemistry) and solution conditions (pH, ionic strength, solvent quality). Numerous investigations have probed the influence of these parameters on the composition and viscoelasticity of PE complexes (PECs). Yet, most studies are restricted to ideal systems comprising charge- and length-matched PEs and monovalent salts. In contrast, in areas where PEs are employed (biological systems, wastewater treatment), little to no control can be exercised over conditions under which complexation occurs, thus limiting the translation of our understanding of PECs into pragmatic settings.

Addressing this gap, the presentation will discuss the effect of salt-ion valency and PE length asymmetry on the composition and viscoelastic behavior of PECs. The phase composition of PECs, in presence of divalent ions, will be shown to stand in stark contrast to monovalent ion complexes. The profound effect of ion valency on PEC chain relaxation and a consequent failure of the time salt superposition approach will be shown. Moreover, PE length asymmetry in charge-matched systems will be shown to non-intuitively influence the salt resistance, composition, and shear response of PECs. This dual approach will further our understanding of PECs and help tune their composition and processability under varying solution conditions and PE lengths.