  The theory of second gradient fluids (which are able to exert shear stresses
also in equilibrium conditions) allows us: (i) to describe both the
thermodynamical and the mechanical behavior of systems in which an interface is
present; (ii) to express the surface tension and the radius of microscopic
bubbles in terms of a functional of the chemical potential; (iii) to predict
the existence of a (minimal) nucleation radius for bubbles. Moreover, the above
theory supplies a 3D-continuum model which is endowed with sufficient structure
to allow the construction of a 2D-shell-like continuum representing a
consistent approximate 2D-model for the interface between phases. In this paper
we use numerical simulations in the framework of second gradient theory to
obtain explicit relationships for the surface quantities typical of 2D-models.
In particular, for some of the most general two-parameter equations of state,
it is possible to obtain the curves describing the relationship between the
surface tension, the thickness, the surface mass density and the radius of the
spherical interfaces between fluid phases of the same substance. These results
allow us to predict the (minimal) nucleation radii for this class of equations
of state.
