text: Surface energy comes into play in wetting phenomena. To examine this, consider a drop of liquid on a solid substrate. If the surface energy of the substrate changes upon the addition of the drop, the substrate is said to be wetting. The spreading parameter can be used to mathematically determine this:
  where  is the spreading parameter,  the surface energy of the substrate,  the surface energy of the liquid, and  the interfacial energy between the substrate and the liquid.
  If , the liquid partially wets the substrate. If , the liquid completely wets the substrate.