  Ionic liquids constrained at interfaces or restricted in subnanometric pores
are increasingly employed in modern technologies, including energy
applications. Understanding the details of their behavior in these conditions
is therefore critical. By using molecular dynamics simulation, we clarify
theoretically and numerically the effect of confinement at the nanoscale on the
static and dynamic properties of an ionic liquid. In particular, we focus on
the interplay among the size of the ions, the slit pore width, and the length
scale associated to the long-range organization of polar and apolar domains
present in the bulk material. By modulating both the temperature and the extent
of the confinement, we demonstrate the existence of a complex reentrant phase
behavior, including isotropic liquid and liquid-crystal-like phases with
different symmetries. We show how these changes impact the relative
organization of the ions, with substantial modifications of the Coulombic
ordering, and their dynamical state. In this respect, we reveal a remarkable
decoupling of the dynamics of the counterions, pointing to very different roles
played by these in charge transport under confinement. We finally discuss our
findings in connection with very recent experimental and theoretical work.
