When a droplet is put on a surface it spreads out, but how fast does it spread and how far can it spread? The ability for a droplet to spread quickly and form a film is important in technological processes such as printing, painting and spraying. Wetting can be enhanced with the use of surfactants, but this isn’t always desirable.
Instead of using surfactants, the wetting of a solid surface can be modified using liquid dielectrophoresis or electrowetting. By changing the surface free energy balance between the surface, liquid droplet and vapour surrounding the droplet, we can wet what would otherwise be a non-wetting surface without needing to modify the surface itself using a non-uniform electric field to enhance and control the wetting of dielectric liquids. This allows a voltage to be used to “dial up” the final state of a droplet. We do not need to wait for a film to form – the difference can be seen in how fast a droplet spreads. The induced wetting is also reversible.