(303e) Charged Polymer Conformations in Polyelectrolyte Complexes

Polyelectrolyte complexes form when oppositely charged polymers are mixed together in aqueous media, resulting in a polymer-rich complex phase coexisting with a polymer-depleted supernatant phase. This process is driven by gains in enthalpy from electrostatic associations between oppositely charged polymers and entropy from the release of bound counter-ions. The complex phase exists as an equilibrium liquid coacervate or a glassy precipitate, depending on the strength of electrostatic interactions. These interactions are in turn mediated by acidity/basicity of the monomers and their distribution along the polymer backbone, as well as the ionic strength and pH of the solution. However, it remains unclear when and why one phase is favored over the other and what conformations individual polyelectrolytes adopt in either complex phase.

In this study, we examined the effects of polyelectrolyte chain length, as well as solution pH and ionic strength on complexation behavior and polyelectrolyte microstructure using a variety of spectroscopic and scattering techniques. Specifically, we used charged homopolymer polypeptides – (poly)-lysine and (poly)-glutamic acid. This model system allows the chain length (20 – 400-mer), side-chain functionality and chirality (L, D) to be tuned while keeping the backbone chemistry constant, thus enabling a systematic investigation of polyelectrolyte chain conformation in both the liquid coacervate and glassy precipitate phases at various ionic strengths. Overall, understanding the microstructure and the underlying forces that drive polyelectrolyte complexation will enable design of novel materials for applications ranging from drug delivery to coatings.