Wetting - High-energy Vs. Low-energy Surfaces

High-energy Vs. Low-energy Surfaces

There are two main types of solid surfaces with which liquids can interact. Traditionally, solid surfaces have been divided into high-energy solids and low-energy types. The relative energy of a solid has to do with the bulk nature of the solid itself. Solids such as metals, glasses, and ceramics are known as 'hard solids' because the chemical bonds that hold them together (e.g., covalent, ionic, or metallic) are very strong. Thus, it takes a large input of energy to break these solids so they are termed “high energy.” Most molecular liquids achieve complete wetting with high-energy surfaces.

The other type of solids is weak molecular crystals (e.g., fluorocarbons, hydrocarbons, etc.) where the molecules are held together essentially by physical forces (e.g., van der Waals and hydrogen bonds). Since these solids are held together by weak forces it would take a very low input of energy to break them, and thus, they are termed “low energy.” Depending on the type of liquid chosen, low-energy surfaces can permit either complete or partial wetting.