Temperature Dependent Scaling Behavior of Poly(ethylene oxide) in an Ionic Liquid [BMIM][BF4] Predicted Using First Principles-Based Force Fields

POSTER

Abstract

Mixtures of polymers with ionic liquids (ILs) exhibit many interesting thermodynamic properties including lower critical solution temperature (LCST) phase behavior, for which a better molecular level understanding is desired. While microscopic insight may be provided by molecular dynamics (MD) simulations, the applicability to polymer/IL mixtures is challenging due to uncertain accuracy of the interaction potentials as well as the significant computational cost. In this work, we develop a cost effective, first-principles united atom (UA) force field for poly(ethylene oxide) (PEO)/[BMIM][BF4] mixtures that importantly allows access to the multi-microsecond simulation time-scales necessary to obtain converged statistics for dillute polymer chains in IL solvents. The UA force field is benchmarked against ab initio calculations without any implicit fitting. We use MD simulations to predict the temperature-dependent scaling of polymer size for single-chain PEO in IL solvent. We find that [BMIM][BF4] changes from a good solvent to a theta solvent for PEO as the temperature increses, which agrees perfectly with recent experiment. We highlight specific coordination structures of the PEO chains enclosing its neighboring BMIM cations to illustrate the entropic mechanism for the LCST.

Presenters

  • Chang Yun Son

    Chemistry and Chemical Engineering, Caltech, Chemistry, Univ. of Wisconsin-Madison

Authors

  • Chang Yun Son

    Chemistry and Chemical Engineering, Caltech, Chemistry, Univ. of Wisconsin-Madison

  • Jesse McDaniel

    Chemistry, Univ. of Wisconsin-Madison

  • Qiang Cui

    Chemistry, Univ. of Wisconsin-Madison

  • Arun Yethiraj

    Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin-Madison, Chemistry, Univ. of Wisconsin-Madison, Univ of Wisconsin, Madison