  Current major approaches to access surface hydrophobicity include directly
introducing hydrophobic nonpolar groups/molecules into surface or elaborately
fabricating surface roughness. Here, for the first time, molecular dynamics
simulations show an unexpected hydrophobicity with a contact angle of $82^o$ on
a flexible self-assembled monolayer terminated only with two hydrophilic OH
groups ($(OH)_2\!-\!SAM$). This hydrophobicity is attributed to the formation
of a hexagonal-ice-like H-bonding structure in the OH matrix of
$(OH)_2\!-\!SAM$, which sharply reduces the hydrogen bonds between surface and
water molecules above. The unique simple interface presented here offers a
significant molecular-level platform for examining the bio-interfacial
interactions ranging from biomolecules binding to cell adhesion.
