When two smooth, slick surfaces are submerged in water and brought within 100 nanometers of each other, something odd happens: they adhere, even though they are too far apart for electrostatic forces to bridge them. C. Jeffrey Brinker of Sandia National Laboratories and his colleagues repeated this experiment with rougher silica surfaces that repel water more than smooth ones do. Using a special kind of atomic force microscope to control the spacing of the surfaces, they found that this strange attraction kicked in at an even longer distance of up to two microns and that it was accompanied by the formation of a vapor bubble in between. The surfaces' antagonism toward liquid water creates a partial vacuum that draws them together, the group concludes in the August 3 Nature.
This article was originally published with the title "Bubble Adhesion" in Scientific American 295, 4, 32 (October 2006)