(304a) Polymers in Ionic Liquids

Ionic liquids have generated considerable excitement for their varied potential applications and their interesting physical properties. The viability of ionic liquids in materials applications is limited by their lack of mechanical integrity, which may be provided by mixing them with a polymeric material.  Recent experiments on polymers in ionic liquids have unearthed a wealth of interesting phenomena that raise fundamental questions.  This paper describes computational studies of PEO in [BMIM] [BF₄].  Atomistic simulations show that the polymer is expanded at room temperature, but coarse-grained models predict the polymer is collapsed.  In an attempt to resolve this discrepancy, we develop a physically motivated first principles force field; this force field is in quantitative agreement with experiment with no adjustable parameters.  The calculations emphasize the importance of polarization but show little evidence for charge transfer.  Atomistic simulations show a lower critical solution temperature in the PEO in [BMIM] [BF₄] system and provide physical insight into the mechanism.  Computational modeling of these systems is tricky because of a delicate balance of different types of interatomic interactions.