[Terminology] Wetting effect and wetting agent
Wetting: Fluid on the solid surface is replaced with another fluid.
Wetting process involves three phases, which includes two fluid phases. Obviously, two fluid phases should not be miscibility; or the solubility of each other is very small. Interface of wetting effect is three-phase interface.
Wetting agent: the substance that can significantly improve fluid replacement ability.
Obviously, wetting agent is a kind of surfactant.
The most common wetting phenomena is which gas on the solid is replaced with liquid. The most common gas is air, the most common liquid is water or aqueous solution.
Wetting is a basic phenomenon, and is widespread.