Decoupling the Effects of Charge Density and Hydrophobicity on the Phase Behavior and Viscoelasticity of Complex Coacervates

Here, we explore the effect of copolymer chemistry on the phase behavior and viscoelasticity of complex coacervates. To this end, we utilized a library of methacrylate copolymers with varying charge densities and hydrophobicity. Our results show that changing the charge density and hydrophobicity drastically affects the phase behavior─with charge density dictating the salt stability and hydrophobicity controlling the polymer concentration of the coacervates. Small-amplitude oscillatory shear measurements were used to study the viscoelastic response of the coacervates, leveraging knowledge of the coacervate phase behavior in tandem with time-salt superposition to construct a series of time-salt-copolymer master curves that highlight the effects of polymer charge density and hydrophobicity. These combined data show evidence of charge-dominated and hydrophobicity-dominated regimes, allowing for an understanding of how copolymer chemistry can be used to tune the mechanical properties of complex coacervates.