(121h) Gibbs Ensemble Monte Carlo Simulations of Oligo(ethylene oxide)/Salt Mixtures

Poly(ethylene oxide) (PEO) is an excellent candidate as one component of polymer electrolyte membranes (PEM) for battery applications. Extensive research has been done to understand the effects of electrolytes on the properties of PEO-based polymers. The addition of salt can cause significant changes in the phase behavior of polymer blends.^1,2 The cohesive energy density (Π_CED) of PEO/electrolyte mixtures and the resulting binary interaction parameter (χ) play a significant role in understanding the phase behavior of polymer electrolyte blends. The PEO/electrolyte system involves strong binding of cations to ether oxygen atoms and less specific anion solvation.³

In this study, configurational-bias Monte Carlo simulations in the Gibbs ensemble are performed to probe the effects of ion type (LiF, LiClO₄, CsF, and CsClO₄), ion concentration, and temperature on the vapor pressure and Π_CED of EO oligomers. Structural analysis of simulation trajectories reveals the dependence of Π_CED on preferential coordination and binding energies between cations and ether oxygens, as well as the extent of ion clustering. Relatively small changes in the vapor pressure of EO oligomers point to a compensation between enthalpic and non-combinatorial entropic contributions.

1. Ren, C. L.; Nakamura, I.; Wang, Z. G. Effects of Ion-Induced Cross-Linking on the Phase Behavior in Salt-Doped Polymer Blends. Macromolecules 2016, 49, 425–431.
2. Xie, S.; Lodge, T. P. Phase Behavior of Binary Polymer Blends Doped with Salt. Macromolecules 2017, 51, 266–274.
3. Wang, Z. G. Effects of Ion Solvation on the Miscibility of Binary Polymer Blends. Phys. Chem. B. 2008, 112, 16205–16213.