(227b) Molecular Dynamics Simulations of H2O and CO2 at An Ionic Liquid Interface: Effect of a Third Component On CO2 Absorption Dynamics

Using classical molecular dynamics simulation techniques, the surface of the ionic liquid 1-n-butyl-3-methylimidaziolium bis(trifluromethylsulfonly)amide ([bmim][Tf2N]) has been simulated with water and carbon dioxide present. Previously the ionic liquid surface had been studied when the surface was exposed to vacuum and to CO2 gas. In this case we study the behavior of the ionic liquid-CO2 system and determine what the effect of water is on the system. First the behavior of the ionic liquid-water binary system was studied. Density profiles with respect to the interface normal, for atoms of the IL and of water, were computed. This indicated orientational tendencies at the interface as well as density accumulation or depletion of various species at the interface. Angular distributions at the interface, for bonds of the IL and water, were computed. These studies demonstrated what effect the water had on the IL interface, and how water itself behaved. To further study the behavior of water on the IL surface, additional studies were performed. The rate of interfacial diffusion for water was calculated from the simulations. Residence time distributions and crossing time distributions for water molecules at the interface were generated. The potential of mean force for a water molecule crossing the interface was calculated using an additional set of thermodynamic integration simulations. CO2 was added to the IL-water system, and the dynamics of absorption and interfacial crossing of CO2 in the three component system were studied. A coefficient for interfacial diffusivity was calculated. Timeframes of the CO2 density profile were generated over the simulation time to illustrate the process of absorption. Also the potential of mean force for CO2 crossing the interface with water present was computed. These results were compared with previously generated results for the behavior of CO2 in the binary CO2-IL system.