Water molecular arrangement at air/water interfaces probed by atomic force microscopy

Different points along hydrophobic surfaces like air bubble interfaces in water when probed by atomic force microscope tips reveal distinct behaviors. At some points along the interface the tip suffers a strong attraction within a range of ∼250 nm away from the interface plane; at other points the interface exerts a medium range repulsive force growing stepwise as the tip approaches the interface plane; consequently, the hydrophobic force is a strong function of position. To explain these results, we propose that the water interface structure is formed by a network of nanosized hydrogen-bond connected cages of water molecules of different sizes.