Theoretical Studies on Temperature-Induced Molecular Rearrangement of Ionic Liquids Under Nanoconfinement

Nanoconfinement is a solution to overcome high cost, high viscosity and slow diffusion rate of bulk ionic liquids. Moreover, the nanoconfined ionic liquids partially solve the leakage problem and enlarge the applications for ionic liquid devices. Also， nanoconfined ionic liquids exhibit different properties comparing to bulk systems. Therefore, understanding the nanoconfined ionic liquid at atomistic level becomes critical. Motivated by Jiang et al.’s experiment (The Journal of Physical Chemistry C 2015, 119, 22724-22731), we systematically simulated nanoconfined [CnMIM][NTf2] where n=2,4,6 and 8 systems at various temperatures using molecular dynamics method. A high throughput modeling and post processing tool is built. Nanotubes with different chiralities, number of walls, diameters and lengths are considered. The origin of temperature induced molecular rearrangement behavior of [C8MIM][NTf2] system is found. Two typical microstructures of confined ionic liquids are identified. We observed that nanotube chiralities, number of walls and lengths do not affect the anions/cations rearrangement behavior. However, nanotube diameter and length of cation side chain are critical to reproduce the temperature-induced center of mass (COM) switching behavior. The confined cation side chain effect and micro configuration switching during temperature increasing process together explained the nonconfined cation/anion rearrangement mechanism. This work should be helpful in expanding the ionic liquids applications where confinement effects and temperature are involved