Molecular
level understanding of the properties of ionic liquids
inside nanopores is needed in order to use ionic liquids for many
applications such as electrolytes for energy storage in electric double-layer
capacitors and dye-sensitized solar cells for conversion of solar
energy. In this study, classical molecular dynamics (MD) simulations
have been performed to investigate the radial distribution, glass
transition, ionic transfer number, and electrical conductivity of
the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate [EMIM][PF6] ionic liquid encapsulated in carbon nanotube (CNT). The
effect of nitrogen as a doping element in CNT on these properties
of [EMIM][PF6] was also investigated by MD simulation,
and the configurational entropy of [EMIM][PF6] encapsulated
in CNT was calculated in absence and presence of nitrogen as a doping
element. The configurational entropy of [EMIM][PF6] encapsulated
in CNT is nonmonotonic versus temperature in both the presence absence
of nitrogen doping. The glass transition of [EMIM][PF6]
encapsulated in CNT is shifted to high temperature with doped nitrogen.
The Green–Kubo formalism was used to calculate the ionic transfer
number of [EMIM][PF6] encapsulated in CNT. Ionic transfer
numbers show a maximum peak for cation transfer and a minimum peak
for anion transfer with temperature. Electrical conductivity of [EMIM][PF6] encapsulated in CNT decreases with increasing temperature
in the presence of doped nitrogen and increases in absence of nitrogen.
The cationic conductivity also increases with temperature in the presence
vs absence of nitrogen doping. The MD findings for electrical conductivity
and glass transition with temperature are in good agreement with available
experimental data. The MD data shed new light on the effect of nitrogen
doping on the mechanism of ion transfer. In the presence of nitrogen,
ion transfer uses a hydrogen bonding mechanism, and in its absence,
ion transfer uses a diffusion mechanism in which the cation has a
significant effect on ion transfer and electrical conductivity.