Conformational Structure of Polyelectrolytes in Polyzwitterionic Coacervate Complexes

Polyelectrolyte coacervarte complexes are formed between oppositely charged polyelectrolytes by releasing screened counterions to aqueous solutions. While much research has strived to understand the phase behaviors, the microstructural details of polyelectrolytes in the coacervate complexes remain unclear. In this work, we examine the conformational structure and local proton concentration of weak polybase, poly(2-vinylpyridine) (P2VP) upon coacervate complexation with zwitterionic poly(sulfobetaine methacrylate) (PSBMA) in KCl aqueous solutions. We have observed that the coacervate phase is much broadened by increasing pH from 2-4 at the same polymer and salt concentrations. The measured hydrodynamic radius of single fluorescence-labeled P2VP chains in the coacervate by fluorescence correlation spectroscopy (FCS) exhibits a swollen conformation with little dependence on solution pH. In contrast, the measured local proton concentration near P2VP shows a non-monotonic change with pH, suggesting possible re-association of released counterions with P2VP. The de-coupling of local proton concentration and conformational structure of weak polyelectrolyte in the coacervate complex is under further investigation with multivalent salt solutions.