surface excess Helmholtz energy

Defined by:

$A σ = U σ − T S σ$

where $U σ$ is the surface excess energy, $T$ is the thermodynamic temperature, and $S σ$ is the surface excess entropy.

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 599