Fine probing the effect of replacing [PF6] with [PF3( C2F5) 3] on the local structure and nanoscale organization of [bmim] plus - based ionic liquids using MD simulation

摘要

Comparative all-atom molecular dynamics simulations are used to study the microscopic local structure and interionic interactions of two ionic liquids (ILs) composed of the 1-butyl-3-methylimidazolium cation, [bmim](+), coupled with the hexafluorophosphate, [PF6](-), or tris(pentafluoroethyl)trifluorophosphate, [FAP](-), anions. Respective distribution functions clearly reveal that the structural correlations between the cation and anion decrease when (i) replacing [PF6](-) with [FAP](-), (ii) scaling the partial atomic charges, and (iii) considering the anion's structural flexibility versus rigidity. Replacement of [PF6](-) with [FAP](-) expands the nonpolar domains totally and causes the decreasing of the three-dimensional polar networks as well as the diminishing of the nano-aggregation of cation side chains. Current simulations show that with increasing the anion size and its charge delocalization, the probability of the in-plane cation-anion conformation, its related hydrogen bond acceptor ability, and the cation-cation - interaction decreases in accordance with the fluidity enhancements of the corresponding imidazolium-based IL. Hence, structural findings can explain and justify rationally the origins of the observed trends in the simulated dynamical properties of these ILs in our previous report. A complete understanding of the microscopic structure of ILs is necessary to control the outstanding properties of ILs as designer solvents that will support experimentalists for the best engineering design and a breakthrough efficiency of IL-related processes.