Effect of Hydrogen Bonds on the Dielectric Properties of Interfacial Water

The dielectric constant for water is reduced
under confinement. Although this phenomenon is well known,
the underlying physical mechanism for the reduction is still in
debate. In this work, we investigate the effect of the
orientation of hydrogen bonds on the dielectric properties
of confined water using molecular dynamics simulations. We
find a reduced rotational diffusion coefficient for water
molecules close to the solid surface. The reduced rotational
diffusion arises due to the hindered rotation away from the
plane parallel to the channel walls. The suppressed rotation in
turn affects the orientational polarization of water, leading to a
low value for the dielectric constant at the interface. We
attribute the constrained out-of-plane rotation to originate
from a higher density of planar hydrogen bonds formed by the interfacial water molecules.