Surface Energy

Also designated "Interface Energy".

Surface energy ist the energy to be invested to break molecular bindings between surface molecules of solids and liquids. If the surface energy is high, the surface has the tendency to attrack other molecules. Liquids with a high surface energy tend to form stable spheric shapes (which is the shape of minimum distance of surface molecules). Liquids with low surface energy keep their surface less in shape and start to flow easier. If a liquid is brought in contact to a solid surface with a higher surface energy, the attraction forces of the solid are higher so that the molecules of the liquid rather spread on the surface than forming a stable sphere.

Surfaces with bipolar character (polar surface) have high surface energy, because the high polar forces strongly attrack other molecules and are wetted easier by liquids.

The unit describing the magnitude of the surface energy is [mJ/m²] = [Millijoule per square meter].

In case of liquids it is more usual to use the designation Surface Tension with the unit [mN/m] = [Millinewton per Meter]. The units of surface tension and surface energy are equivalent (1 J = 1 Nm). In many publications also the surface energy of solids is expressed by the unit [mN/m].

Surface Tension
The liquid doesn't wet the surface with low surface energy.