  The classical theory of Laplace is not suitable for describing the behavior
of microscopic bubbles. The theory of second gradient fluids (which are able to
exert shear stresses in equilibrium conditions) allows us to obtain a new
expression for surface tension and radius of these bubbles in terms of
functionals of the chemical potential. This relationship allows us to
generalize the results of Cahn-Hilliard and Tolman.
