surface excess, \(n^{\sigma}\)

https://doi.org/10.1351/goldbook.S06171
For an @I03082@, the adsorption or surface excess of a given component is defined as the difference between the amount of component actually present in the system, and that which would be present (in a reference system) if the bulk concentration in the adjoining phases were maintained up to a chosen geometrical @D01823@ (@G02635@). For a solid/liquid @I03082@ in which no component of the liquid phase penetrates into the solid, the surface excess (or adsorption) of component i is defined as: \[n_{i}^{\sigma }=n_{i}- V^{\text{l}}\ c_{i}^{\text{l}}\] where \(n_{i}\) is the total amount of i in the system, \(V^{\text{l}}\) is the volume of an arbitrarily chosen amount of bulk liquid (in the framework of the so-called algebraic method) and \(c_{i}^{\text{l}}\) is its bulk concentration in the liquid.
See:
Gibbs adsorption
,
Gibbs surface
,
interface
Sources:
Green Book, 2nd ed., p. 63 [Terms] [Book]
PAC, 1986, 58, 967. (Reporting data on adsorption from solution at the solid/solution interface (Recommendations 1986)) on page 969 [Terms] [Paper]