The Hydrophobic Gap at High Hydrostatic Pressures

We gain new insight into the so-called hydrophobic gap, a molecularly thin region of decreased electron density at the interface between water and a solid hydrophobic surface, by X-ray reflectivity experiments and molecular dynamics simulations at different hydrostatic pressures. Pressure variation shows that the hydrophobic gap persists up to a pressure of 5 kbar. The depletion in the interfacial region is strongly decreasing with rising pressure, indicating that the interfacial region is compressed more strongly than bulk water. The decrease is most significant up to 2 kbar, beyond that, the pressure response of the depletion is less pronounced.