Static and dynamic correlations in water at hydrophobic interfaces

We study the static and dynamic properties of the water-density fluctuations in the interface of large nonpolar solutes. With the help of extensive molecular dynamics simulations of TIP4P water near smooth spherical solutes, we show that for large solutes, the interfacial density profile is broadened by capillary waves. For purely repulsive solutes, the squared width of the interface increases linearly with the logarithm of the solute size, as predicted by capillary-wave theory. The apparent interfacial tension extracted from the slope agrees with that of a free liquid-vapor interface. The characteristic length of local density fluctuations is approximate to 0.5 nm, measured along the arc, again consistent with that of a free liquid-vapor interface. Probed locally, the interfacial density fluctuations exhibit large variances that exceed those expected for an ideal gas. Qualitatively consistent with theories of the free liquid-vapor interface, we find that the water interface near large and strongly nonpolar solutes is flickering, broadened by capillary-wave fluctuations. These fluctuations result in transitions between locally wet and dry regions that are slow on a molecular time scale.