Studying Interfacial Phenomena of Ionic Liquids Using Accurate Dynamics Coarse-Grained Models*

The increased attention and utilization that Ionic Liquids (ILs) have gained in the last couple of decades has been fueled by realization of their useful and unique physical and chemical properties. All-atom molecular dynamics (MD) simulations have adapted to produce coarse-grained (CG)  simulation models for more computationally efficient computation of various systems. However, majority of CG methods will not necessarily reproduce correct dynamic behavior of CG system, because "effective friction" between CG sites is underestimated along with reduced degrees of freedom in the system. To address this issue, the more recently developed probability distribution function based coarse-graining (PDF-CG) method has been implemented. In this method effective friction reintroduced ito the CG system throught stochastic Langevin equation. With the proposed approach accurate prediction of structure and dynamics for CG systems like ILs has been observed. The present work details studying behaviour of two ILs at liquid-vacuum interface. Two sets of ILs of interest are: (a) N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)-imide ([pyr14][TFSI]), and (b) 1-ethyl-3-methylimidazolium boron tetrafluoride ([EMIM][BF₄]). First outlined is the development and validation of CG models, in which CG force fields were successfully obtained to produce correct structure and dynamics of CG system for both liquids. Next, the CG models of ILs were used to study behavior of ILs at liquid-vacuum interface.