Principal Scientist of VTT Technical Research Centre of Finland, Dr. Lasse Makkonen has explained the frictional mechanism that resists the motion of drops on inclined surfaces and when affected by wind drag, and developed a theory by which sliding of drops off surfaces of different materials can be predicted. This makes it possible to systematically develop hydrophobic surfaces by modifying their base material and roughness.
Sliding of drops off surfaces affects the water repellency of clothing, visibility through wind screens in rain, and many industrial processes. Hence, wettability of materials is one of the most researched problems in the world.
A major problem has been that according to the force balance of a drop on a surface, proposed by Thomas Young in 1805, even the smallest external force should make the drop slide, but this does not happen in practice no matter how smooth the surface is.
The theory by Dr. Makkonen has been published in Journal of Physics: Condensed Matter and The Journal of Chemical Physics. These papers are freely accessible at: http://iopscience.iop.org/article/10.1088/0953-8984/28/13/135001/meta and http://dx.doi.org/10.1063/1.4996912.
The research was funded by the Academy of Finland.