The role of surface energy in materials science
Surface tension of liquid metals and capillarity

The ability of a liquid to wet the surface of a solid is quantified by the contact angle θ formed at equilibrium at the junction line of three phases: solid S, liquid L and vapor V (figure 1a). A liquid is either non-wetting or wetting, depending on whether its contact angle with the solid under consideration is greater or less than 90°. The special case θ = 0° is called "perfect wetting", when the liquid forms a stable film on the solid. The contact angle θ_Y formed on a perfectly smooth, chemically homogeneous solid is governed by Young's equation: