Correlation and Association Effects of Ions in Block Copolymers from Fluids Density Functional Theory

Ion containing block copolymers have potential application as solid-state, nonflammable battery electrolytes and in other charge transport applications, such as electroactive actuators. In these systems, ion clustering and preferential solvation into the microphase with the higher dielectric constant strongly affect on the polymer phase behavior; even a small amount of salt can significantly increase the effective segregation strength between the blocks. Additionally, Lithium ions can strongly complex with the ether Oxygens (EO) in polymers such as polyethylene oxide. To model these effects, we implement a coarse-grained model using fluids density functional theory. Ion correlations are introduced using the direct correlation function of a reference fluid of unbonded monomers and salt, obtained by solving the Ornstein-Zernike equation with the hypernetted-chain closure, and Li-EO complexation is modeled using an extension of the inhomogeneous statistical associating fluid theory (iSAFT). By turning these individual effects on and off, we show how each contributes to the phase behavior of these polymer systems.