  We present a theoretical study of the influence of the molecular geometry of
the cation on the response of ionic liquid (IL) to confinement and mechanical
strain. The so-called {\it tailed} model includes a large spherical anion and
asymmetric cation consisting of a charged head and neutral tail. Despite its
simplicity, this model recovers a wide range of structures seen in IL: simple
cubic lattice for the small tails, liquid-like state for symmetric cation-tail
dimers, and molecular layer structure for dimers with large tails. A mutual
feature of all investigated model ILs is a formation of the fixed (stable)
layer of cations along solid plates. We observe single anionic layer for small
gap widths, double anionic layer for intermediate, and tail--to--tail layer
formation for wide gaps. The normal force evolution with the gap size can be
related to the layer formed inside the gap. The low hysteretic losses during
the linear cyclic motion suggest the presence of strong slip inside the gap. In
our model specific coefficient of friction is low and friction force decreases
with the tail size.

Soft Condensed Matter;Materials Science;Applied Physics;Chemical Physics;Computational Physics