Fractal Structures

Copper film grown using diffusion limited aggregation

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.

Droplet on electrodeposited surface
Droplet on electrodeposited surface
SEM of electrodeposited surface tilted at 70°

Read more about the process in the paper below.