On the rheology of a liquid-vapor interface

TL;DR

This paper provides a theoretical analysis of the rheology at liquid-vapor interfaces, clarifying the location of the surface phase for different surfactant types using Gibbs' model.

Contribution

It introduces a theoretical framework comparing rheological models to determine the interface location in two-component systems with surfactants.

Findings

Surface phase for insoluble surfactants coincides with the equimolecular interface.

For soluble surfactants, the surface phase is at zero excess total mass density.

The surface phase is close to the surface of tension and kinematic surface.

Abstract

The mass and momentum balances are theoretically studied in heterogeneous two-component systems. Following Gibbs the system is presented as two bulk and a single surface phases. Comparing the equations derived with some typical rheological models, useful information about the location of the interface is obtained. It was demonstrated that the surface phase for insoluble surfactants coincides with the equimolecular interface, while for soluble ones it is placed on the surface of total mass density zero excess. In both cases the surface phase is close to the surface of tension and kinematic surface.