Density evolution at fluid-fluid interfaces: A generalized Gibbs-Duhem theory
arXiv:2607.11988
The paper derives a generalized Gibbs‑Duhem relation that includes kinetic effects and uses it to formulate a new density‑evolution equation for fluid‑fluid interfaces, which reproduces known results such as the speed of sound, Bernoulli’s law, and the van der Waals equation in limiting cases.
Abstract
The classical Gibbs-Duhem relation applies to quasi-static processes and neglects kinetic effects, leaving a fundamental gap between Gibbs thermodynamics and Newtonian mechanics. Here, we derive a generalized Gibbs-Duhem framework that incorporates kinetic contributions, thereby establishing a unified connection between classical thermodynamics and Newtonian mechanics. Based on this framework, we propose an alternative evolution equation governing density dynamics at fluid-fluid interfaces. In appropriate limiting cases, the resulting density evolution equation naturally recovers the definition of the speed of sound, Bernoulli's law, and the van der Waals equation of state (EOS).