Flow at the nanoscale: what stops a drop and keeps nanobubbles alive
Max Planck researchers from Stuttgart present first model calculation
April 12, 2016
All of us have seen it: a raindrop running down the windowpane. It stops at a certain point, is met by a second raindrop and the two join up before continuing to run down the pane. Very small irregularities or dirt on the windowpane appear to stop the course of the raindrops. If the surface was entirely smooth and chemically clean, the raindrops would be able to flow unhindered. Surface defects such as small bumps and dimples as well as chemical contaminants stop the liquid drops. These are everyday phenomena everyone knows and can observe with the naked eye.
However, for years, progress in science and technology has been directed towards ever more finely structured surfaces of solids which can be used for a wide variety of applications. Here the typical structure dimensions are in the micrometer or even the nanometer range (a nanometer is one-millionth of a millimeter).
But how is the flow behavior of a drop influenced by such fine surface structures, and how is the transportation of tiny amounts of liquid on extremely narrow paths impeded by tiny surface defects along this path? Here the surface defects in question are not much larger than the molecules or atoms which form he liquid or the surface of the solid. The influence of such small surface defects on the transportation of liquids cannot be studied with the naked eye. Even with sophisticated modern experimental methods, it is currently not possible to observe and investigate the transportation of liquids across such small surface defects. Theoretical methods and model calculations overcome this challenge.
The research department “Theory of inhomogeneous condensed matter” headed by Prof. Dr. Siegfried Dietrich at the Max Planck Institute for Intelligent Systems in Stuttgart has developed a model calculation which incorporates the relevant molecular structure on the nanometer scale. This theoretical model makes it possible to calculate the resistance against the transportation of liquids caused by irregularities or contaminants of a few nanometers in size.
Dr. Alberto Giacomello and Dr. Lothar Schimmele along with Professor Dr. Siegfried Dietrich recently published these results in the journal “Proceedings of the National Academy of Sciences” (PNAS).
This multidisciplinary journal of international renown only publishes studies of extraordinary scientific importance. They also have to be of general interest for other groups of specialists, in this case for example scientists in the fields of microfluidics, nanostructure physics and surface chemistry.