(387b) Influence of Hydrophilic Surface Specificity On the Structural Properties of Confined Water

The influence of chemical specificity of hydrophilic surfaces on the structure of confined water

in the sub-nanometer regime is investigated using grand ensemble Monte Carlo simulations.

The structural variations for water confined between hydroxylated silica surfaces are contrasted

with water confined between mica surfaces. Although both surfaces are hydrophilic, our study

shows that hydration of potassium ions on the mica surface has a strong influence on the water

structure and solvation force response of confined water. In contrast to the disrupted hydrogen

bond network observed for water confined between mica surfaces, water between silica

surfaces retain their hydrogen bond network displaying bulk-like structural features down to

surface separations as small as 0.45 nanometer (nm). Hydrogen bonding of an invariant contact water layer

with the surface silanol groups aids in maintaining a constant number of hydrogen bonds per

water molecule for the silica surfaces. As a consequence, water depletion and rearrangement

upon decreasing confinement is a strong function of the hydrophilic surface specificity, particularly

at smaller separations. An oscillatory solvation force response is only observed for water

confined between silica surfaces and bulk-like features are observed for both surfaces above a

surface separation of about 1.2 nm. We evaluate and contrast the water density, dipole moment

distributions, pair correlation functions and the solvation forces as a function of the surface

separation.