Molecular dynamics simulations of the ionic liquid [EMIM+][TFMSI−] confined inside rutile (110) slit nanopores

Abstract

The structure and dynamics of the ionic liquid (IL) [EMIM(+)][TFMSI(-)] inside a rutile (110) slit nanopore of width H = 5.2 nm at T = 333 K are studied using classical molecular dynamics (MD) simulations. These results are compared against those obtained in our previous study (N. N. Rajput et al., J. Phys. Chem. C, 2012, 116, 5169-5181) for the same IL inside a slit graphitic nanopore of the same width. Electrostatic and dispersion interactions are present between the IL and the rutile walls, whereas only weaker van der Waals interactions are present between the IL and the graphitic walls. Our results suggest that the strength of the interactions between the pore walls and the IL can significantly affect the structure and dynamics of the confined IL. Layering effects were more pronounced for the IL inside a rutile pore as compared to inside a graphitic pore. The ions near the rutile pore walls had a liquid structure that was significantly different from that of the bulk IL; in contrast, the same ions near graphitic pore walls had a liquid structure that was similar to that of the bulk IL. Cations and anions adopted multiple orientations near the rutile walls, which contrast with the parallel orientations that were uniformly observed for the same ions near graphitic walls. The dynamics of [EMIM(+)][TFMSI(-)] inside a slit rutile pore are significantly slower than those observed inside a slit graphitic pore. Near the rutile walls, the dynamics of the ions were about an order of magnitude slower than those of ions near graphitic walls. The ions in the center of a rutile pore exhibit enhanced mobilities, but still about 2-4 times slower than those observed for ions in the center of a graphitic pore. The effects of variations in the amount of IL on the dynamics were very marked inside a rutile pore, with reductions of up to 4 times in the mobilities of the ions in the different regions of the pore; in contrast, pore loading seems to cause smaller variations in the dynamics of ILs inside a graphitic slit nanopore.