How Spherical Polyelectrolyte Brush Structure Affects the Formulation of Nanoparticle-Integrated Coacervates

Complex coacervates, formed by the association oppositely charged polyelectrolyte chains, are complex fluids with diverse applications. These coacervates are typically charge-balanced and expel or aggregate charged nanoparticles. Here we show that for solutions of nanoparticles functionalized with tethered polyelectrolyte chains, addition of an oppositely charged polyelectrolyte produces a nanoparticle-integrated coacervate. Nanoparticle-integrated coacervates qualitatively resemble those made of linear chains in terms of their appearance and phase diagram. Nanoparticle-integrated coacervated, are, however, quantitatively distinct in having a larger salt resistance and, therefore, a larger two phase region. Different from linear polymeric coacervates, nanoparticle-integrated coacervates made with polyanion-functionalized nanoparticles are consistently charged-imbalanced with excess polycation. Most striking, the coacervate is not space filling, and analysis of the particles and coacervate composition suggests substantial spacing between coacervate coronas of neighboring particles, with interstitial space occupied by polycation solution. The amount of charge mismatch is related to brush structure and estimates of interstitial volume beyond the coronas.