wetting tension (or work of immersional wetting per unit area)

The work done on a system when the process of immersional wetting involving unit area of phase β is carried out reversibly:

$w W α β δ = γ β δ − γ α β$

where $γ α β$ and $γ β δ$ are the surface tensions between two bulk phases α, β and β, δ, respectively.

Source:

PAC, 1972, 31, 577 (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 598