Surface energy

Surface energy is the energy required to break up the molecular bonds of the surface and the liquid. If the surface energy is high, the molecules have a high tendency to attract other molecules . Liquids with a high surface energy have the tendency to contract to form a stable spherical shape (shape in which the surface molecules are at the lowest possible distance). Liquids with a low surface energy do not contract to form a stable shape and dissolve more easily. If liquids come into contact with surfaces with a high surface energy, the attraction exercised by the surface molecules on the liquid molecules is stronger than the latter’s bond to each other. This is why liquids with a low surface energy dissolve on surfaces with a high surface energy. Surfaces with dipolar properties (polar surfaces) have high surface energies because the exercise strong dipolar forces on other molecules ; therefore, liquids can wet them more easily. The unit for surface energy is energy for area unit: [mJ/m²] = [millijoule per square meter]. In case of liquids, the term surface tension is commonly used [mN/m] = [millinewton per meter]. The term has the same physical significance (1 J = 1 Nm). The surface energy of solid bodies is often expressed in the dimension [mN/m].