A simple school science experiment is to electroplate an object with copper using a copper sulphate solution. If a little bit of sulphuric acid is added and the current density is chosen carefully, the growth of a film of copper can be controlled by a process called diffusion limited aggregation. This produces a dendritic structure type of growth whereby bumps grow on bumps and branches grow on branches, thus creating a very rough surface.
When this type of surface is provided with a hydrophobic surface chemistry, it creates a surface on which droplets of water completely ball up and freely roll-off. Read more about the process in the paper below, and read more about fractals at Wikipedia.
- Wetting and wetting transitions on copper-based super-hydrophobic surfaces.
N.J. Shirtcliffe, G. McHale, M.I. Newton, G. Chabrol and C.C. Perry.
Langmuir. 21 (3) (2005) 937-943.