  Ionic liquids have generated interest in applications as lubricants and as
additives to conventional lubricants due to their unique physical properties.
In these applications, the liquid thin film can be subjected simultaneously to
extremely high shear and loads in addition to nanoconfinement effects. Here, we
use molecular dynamics simulations with a coarse grained model to study a
nanometric film of an ionic liquid confined between two planar solid surfaces
both at equilibrium and at several shear rates. The strength of the interaction
between the solid surface and the ions was changed by simulating three
different surfaces with enhanced interactions with different ions. The increase
of the interaction with either the cation or the anion leads to the formation
of a solid-like layer that moves alongside the substrates, but this layer can
exhibit different structures and stability. An increase in interaction with the
high symmetry anion produces a more regular structure that is more resistant to
the effects of shear and viscous heating. Two definitions were proposed and
used for the calculation of the viscosity: a local definition based on
microscopic characteristics of the liquid and an engineering definition based
on the forces measured at the solid surfaces, with the former displaying a
correlation with the layered structure induced by the surfaces. Because of the
shear thinning behavior of the ionic liquids as well as the temperature rise
brought on by viscous heating, both the engineering and the local viscosities
decrease as the shear rate increases.
