  We report on simulations of capillary filling of high-wetting fluids in
nano-channels with and without obstacles. We use atomistic (molecular dynamics)
and hydrokinetic (lattice-Boltzmann) approaches which point out clear evidence
of the formation of thin precursor films, moving ahead of the main capillary
front. The dynamics of the precursor films is found to obey a square-root law
as the main capillary front, z^2(t) ~ t, although with a larger prefactor,
which we find to take the same value for the different geometries (2D-3D) under
inspection. The two methods show a quantitative agreement which indicates that
the formation and propagation of thin precursors can be handled at a
mesoscopic/hydrokinetic level. This can be considered as a validation of the
Lattice-Boltzmann (LB) method and opens the possibility of using hydrokinetic
methods to explore space-time scales and complex geometries of direct
experimental relevance. Then, LB approach is used to study the fluid behaviour
in a nano-channel when the precursor film encounters a square obstacle. A
complete parametric analysis is performed which suggests that thin-film
precursors may have an important influence on the efficiency of
nanochannel-coating strategies.
