Integrated Calendar

Hydrophobic surfaces are common in nature and technology. Surfactant monolayers are a standard method of hydrophobizing surfaces, andinteractions between such monolayer-coated surfaces have been measured directly for decades: but they are not well understood. One frequent but puzzling observation is that of long-ranged (up to 100 nm) attractions between such surfaces across water, which are orders of magnitude larger than van der Waals forces. This was long attributed to water structuring near the hydrophobic surfaces, but such structuring is unlikely to exceed some nanometers at most. We now elucidate the origin of these long-ranged attractions, which resides in a subtle and counterintuitive electrostatic effect, even between overall neutral surfaces.