Brushing Up on Coacervates: How Chain Anchoring Can Incorporate Solid Particles into Fluid Polyelectrolyte Complexes*

When charged solid particles are combined with an oppositely charged polyelectrolyte in an aqueous suspension/solution, Coulombic attractions (and counterion release) drive polymer adsorption and intractable (kinetically-trapped) particle aggregation.  In contrast, combination of two oppositely charged polyelectrolytes in aqueous solution often forms a fluid complex (“complex coacervate”) described by an equilibrium thermodynamic phase diagram in which salt concentration appears as a temperature variable.  We attach the chain ends of a polyanion oligomer to nanoparticles and form complex coacervates upon addition of a polycation.  The work probes the numbers and concentrations of tethered chains in the polyanion brush needed to facilitate solid nanoparticle incorporation into the coacervate.  We find that without sufficient bound chains, aggregates rather than a complex coacervate is formed.