Effect of Charge Density and Topology on Polyelectrolyte Complex Coacervation*

An aqueous solution of oppositely-charged polyelectrolytes can undergo associative phase separation into polyelectrolyte-dense and polyelectrolyte-dilute phases, a process known as complex coacervation. Recently, there has been a resurgence of interest in predicting the effect of the polyelectrolytes' molecular features on coacervation, driven by new efforts in theory and computation. In particular, chain length, charge density and charge spacing have been examined, alongside the polyelectrolyte and salt concentrations in solution. Experimental coacervation studies have either employed polydisperse statistical copolymers or, more recently, recombinant protein segments with deterministic sequence. Using polypeptoids with a controlled monomer sequence and lack of backbone hydrogen bonding as model polyelectrolytes, we examine the effect of charge density and topology (spacing and grouping of charges) on coacervation. In addition, we compare the experimental results with the theoretical models, and discuss discrepancies and current limitations.