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Abstract
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A coarse-grained (CG) model for the simulation of nanoconfined
water between graphene surfaces is developed. For this
purpose, mixed-grained simulations are done, in which the
two-site water model of Riniker and van Gunsteren [S. Riniker,
W. F. van Gunsteren, J. Chem. Phys. 2011, 134, 084110] is simulated
between atomistically resolved graphene surfaces. In the
developed pure CG model, the two interaction sites of water
and a combination of eight carbon atoms in the graphene surface
are grouped together to construct water and surface CG
beads. The pure CG potentials are constructed by iteratively
matching the radial distribution functions and the density profiles
of water beads in the pore with the corresponding mixedgrained
distributions. The constructed potentials are shown to
be pore-size transferable, capable of predicting structural properties
of confined water over the whole range of pore sizes,
ranging from extremely narrow pores to bulk water. The
model is used to simulate a number of nanoconfined systems
of a variety of pore sizes at constant temperature, constant
parallel component of pressure, and constant surface area of
the confining surfaces. The model is shown to predict the
layering of water in contact with the surfaces, and the solvation
force is in complete agreement with the mixed-grained
model. It is shown that water molecules in the pore have
smaller parallel diffusion coefficients compared to bulk water.
Well-organized layers beside the surfaces are shown to have
lower diffusion coefficients than diffuse layers. More information
on the dynamics of water in the pore is obtained by calculating
the rate of water exchange between slabs parallel to the
surfaces. The time scale to achieve equilibrium for this process,
depending on the pore width and on the degree of layering of
water beside the surfaces, is a few nanoseconds in nanometric
pores.
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