Publication of the Chemistry Laboratory in the journal Nature Comunication on April 1st, 2023. Communication of the CNRS-INC on April 20, 2023.
Historically developed for macroscopic systems, thermodynamics is the science that allows to precisely define pressure and temperature by focusing on a system's energy flows. A CNRS researcher from the Chemistry Laboratory of ENS de Lyon has shown that the definition of some fundamental quantities becomes much more complicated for nanometric systems. A study published as a featured article in the journal Nature Communications.
Disjoining pressure was discovered by Derjaguin in 1930’s, which describes the difference between the pressure of a strongly confined fluid and the corresponding one in a bulk phase. It has been revealed recently that the disjoining pressure is at the origin of distinct differential and integral surface tensions for strongly confined fluids. Here we show how the twin concept, disjoining chemical potential, arises in a reminiscent way although it comes out eighty years later. This twin concept advances our understanding of nanoscale thermodynamics. Ensemble-dependence (or environment-dependence) is one hallmark of thermodynamics of small systems. We show that integral surface tension is ensemble-dependent while differential surface tension is not. Moreover, two generalized Gibbs-Duhem equations involving integral surface tensions are derived, as well as two additional adsorption equations relating surface tensions to adsorption-induced strains. All the results obtained in this work further evidence that an approach alternative of Hill’s nanothermodynamics is possible, by extending Gibbs surface thermodynamics instead of resorting to Hill’s replica trick. Moreover, we find a compression-expansion hysteresis without any underlying phase transition.
Illustration : iStock, credits: Jian Fan