Static dielectric permittivity of ionic liquids ultraconfined in carbon nanotubes

In this work the parallel component of the static dielectric permittivity, ϵ II of ionic liquids ultraconfined into flexible carbon nanotubes of radius of 1.2 nm and 2.4 nm is evaluated from molecular dynamics simulations. We show an enhancement of ϵ II with respect to bulk value and a counter-intuitive temperature dependence. Indeed an increase of ϵ II as a function of the temperature opposed to a bulk behavior is evidenced. Increase in ϵ II is the result of the strong orientation of ionic liquid close to the pore wall. The temperature dependence is the consequence of the thermal fluctuations increasing the dipolar fluctuations such that the strong orientation is conserved. Eventually, we show a molecular stacking between [C 4 mim + ][Tf 2 N − ] and CNT decreasing dipolar fluctuations close to the CNT surface reducing ϵ II .