3. Surface thermodynamics

Interfaces pose very specific thermodynamic problems, since their very existence is linked to an energy whose precise definition (and even more so its experimental measurement) presents particular difficulties. Although J. W. Gibbs drew attention to some of them as early as the end of the 19th century, a number of important points have not yet been sufficiently clarified; this is particularly true of the notions of tension, stress, surface energy and so on. The identity or, on the contrary, the difference between some of these quantities is not always clear, and even the notations, which differ from one work to another, can pose serious problems. . It is therefore always advisable to refer to the definitions of each quantity when consulting an article.

This paragraph describes equilibrium situations, which are not necessarily the case in practice,...