Nanobubbles and their role in slip and drag

Atomic force microscope images of flat solid surfaces in water reveal that very soft objects can be formed on the surfaces. These objects are nanobubbles of gas with sizes ranging from 10 nm to several micrometers. The bubbles are stable to dissolution, lasting for several hours. In this paper we review some of the methods that allow their generation and observation using the atomic force microscope. Next, we describe the influence of the bubbles on liquid slip close to a hydrophobic surface. The influence of liquid-gas menisci, formed as a result of nanobubbles being present on the surface, on drag reduction is also discussed. Finally, data of liquid flow probed on bubbles entrapped on microstructured surfaces are presented