Structure, Chain Conformations and Dynamics of Polyelectrolyte Complexes

Investigations of structure, chain conformations and dynamics in polyelectrolyte complex (PEC) comprising model polyelectrolytes are presented. The use of charged polypeptides – (poly)-lysine and (poly)-glutamic acid allowed facile tuning of the system parameters, including chain length. side-chain functionality and chirality, while preserving the backbone architecture and chemical structure. Systematic studies using small-angle X-ray scattering (SAXS) of the structure and chain behavior in liquid PEC coacervates revealed a physical description of these materials similar to strongly screened semidilute solutions of polyelectrolytes comprising oppositely charged chains. At the same time, solid PECs were found to be composed of hydrogen-bonding driven stiff ladder-like structures with large correlation lengths. While the liquid complexes behaved akin to semidilute polyelectrolyte solutions upon addition of salt, the solids were largely unaffected by it. The dynamics of the chains in PEC coacervates, explored by rheology measurements, revealed a Maxwell liquid-like behavior. Time-salt superposition led to excellent superposition of the dynamic moduli data, although with the shift factors varying more strongly than previously reported with increasing salt concentration.