Gibbs adsorption

https://doi.org/10.1351/goldbook.G02627
The
surface excess
amount or Gibbs adsorption of component i, niσ, which may be positive or negative, is defined as the excess of the amount of this component actually present in the system over that present in a reference system of the same volume as the real system and in which the bulk concentrations in the two phases remain uniform up to the
Gibbs dividing surface
. That is niσ=niVα ciαVβ ciβ where ni is the total amount of the component i in the system, ciα and ciβ are the concentrations in the two bulk phases α and β, and Vα and Vβ are the volumes of the two phases defined by the
Gibbs surface
.
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 588 [Terms] [Paper]