Phase diagrams of nonionic foam films: New interpretation of disjoining pressure vs thickness curves

Recently we constructed phase diagrams for thin foam films stabilized by a nonionic surfactant. The idea was born by synopsis of various disjoining pressure (Pi) versus thickness (h) curves of foam films resembling p-V-m isotherms of real gases. The new concept of interpreting the Pi-h curves of foam films in terms of phase diagrams allows us to describe experimental observations much more precisely. Three logical consequences will be discussed here to illustrate the strength of this approach. First, the observation is explained that common black films (CBF) rupture or form a Newton black film (NBF) within a certain pressure range rather than at a defined pressure. Both observations can be rationalized by invoking a nucleation process of holes or of the thinner NBF, respectively, in close analogy to the vapor to liquid condensation. Second, the question whether the CBF to NBF transition is discrete or continuous is answered by analyzing under which conditions the supercritical state of a foam film can be reached. Third, the evidence of corresponding states is discussed.