A simple 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 fractal structure whereby bumps grow on bumps and branches grow on branches. The result is 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.
- Super-water-repellent fractal surfaces T. Onda, S. Shibuichi, N. Satoh K. Tsujii, Langmuir 12 (1996) 2125-2127
- 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 (2005) 937-943