  We have studied the molecular scale hydrophobicity of an apolar solute,
argon, confined between hydrophobic planar surfaces with different confinement
widths. Specifically, we find that the hydrophobicity exhibits a non-monotonic
behavior with confinement width. While hydrophobicity is usually large compared
to bulk value, we find a narrow range of confinement width where the
hydrophobicity displays similar values as in bulk water. Furthermore, we
develop a simple model taking into account the entropic changes in nanoconfined
geometry, which enables us to calculate potential of mean force between solutes
as the conditions change from bulk to different degrees of planar
nanoconfinement. Our results are important in understanding nanoconfinement
induced stability of apolar polymers, solubility of gases, and may help design
better systems for Enhanced Oil Recovery.
