Molecular dynamics simulation studies of CO2 – [bmim][PF6] solutions: Effect of CO2 concentration

Molecular dynamics simulations have been carried out on CO2 – [bmim][PF6] mixtures using a refined atomistic potential model for the ionic liquid, at different concentrations of CO2. The expansion in volume as a function of added CO2 was found to agree well with experiments at all but the highest concentration. Significant concentration dependent differences in the radial distribution function of CO2 around the anion have been observed. These differences have been attributed to the specific interaction between CO2 and the anions. The diffusion coefficients of the ions and of CO2 have been found to increase with increase in CO2 concentration. The rotational relaxation of CO2 molecule in solution is found to be biexponential, and the mean relaxation times decreases with increasing CO2 concentration.