  Understanding intrusion and extrusion in nanoporous materials is a
challenging multiscale problem of utmost importance for applications ranging
from energy storage and dissipation to water desalination and hydrophobic
gating in ion channels. Including atomistic details in simulations is required
to predict the overall behavior of such systems, because the statics and
dynamics of these processes depend sensitively on microscopic features of the
pore such as the surface hydrophobicity, geometry, and charge distribution and
on the composition of the liquid. On the other hand, the transitions between
the filled (intruded) and empty (extruded) states are rare events which often
require long simulation times difficult to achieve with standard atomistic
simulations. In this work, we explored the intrusion and extrusion processes by
a multiscale approach in which the atomistic details of the system, extracted
from molecular dynamics simulations, inform a simple Langevin model of water
intrusion/extrusion in the pore. We then used the Langevin simulations to
compute the transition times at different pressures, validating our
coarse-grained model by comparing it with nonequilibrium molecular dynamics
simulations. The proposed approach reproduces experimentally relevant features
such as the time and temperature dependence of the intrusion/extrusion cycles,
as well as specific details about the shape of the cycle. This approach also
drastically increases the timescales that can be simulated allowing to reduce
the gap between simulations and experiments and showing promise for more
complex systems.
