The equation of motion and the conditions on surfaces and edges between fluids and
solids in the presence of nonconstant
surface energies, as in the case of
surfactants
attached to fluid particles at the interfaces, are revisited under the principle of virtual
work. We point out that adequate behaviors of surface concentrations may drastically
modify the
surface tension which naturally appears in the Laplace and the
Young–Dupré equations. Thus, the principle of virtual work points out a strong
difference between the two revisited concepts of surface energy and surface
tension.
