  We determine the surface tension of aqueous electrolyte solutions in contact
with non-polar dielectric media using a thermomechanical approach, which
involves deriving the stress tensor from the thermodynamic potential of an
inhomogeneous fluid. To obtain the surface tension, we calculate both the
normal and tangential pressures using the components of the stress tensor,
recently derived by us [Y. A. Budkov and P. E. Brandyshev, The Journal of
Chemical Physics 159 (2023)] within the framework of Wang's variational field
theory. Using this approach, we derive an analytical expression for the surface
tension in the linear approximation. At low ionic concentrations, this
expression represents the classical Onsager-Samaras limiting law. By utilizing
only one fitting parameter, which is related to the affinity of anions to the
dielectric boundary, we can approximate various experimental data regarding the
surface tension of aqueous electrolyte solutions. This approximation applies to
both the solution-air and solution-dodecane interfaces, covering a wide range
of electrolyte concentrations.
