Water in Contact with Extended Hydrophobic Surfaces: Direct Evidence of Weak Dewetting

X-ray reflectivity measurements reveal a significant dewetting of a large hydrophobic paraffin surface floating on water. The dewetting phenomenon extends less than 15 Å into the bulk water phase and results in an integrated density deficit of about one water molecule per $25–30{\AA }^2$ of water in contact with the paraffin surface. The results are supported by molecular dynamics simulations and related to the hydrophobic effect.