THREE COMPONENTS, FOUR PHASES. WHAT DOES GIBBS' PHASE RULE STATE?

摘要

We have observed (Ishikawa et al J. Phys. Chem. B, 120, 6074-6079, 2016) four phases apparently at equilibrium for a three component microemulsion system at constant temperature and pressure. Applying Gibbs' phase rule in the conventional way gives minus one degree of freedom implying a non-equilibrium situation. Is there another explanation? Through an analysis of the fundamental basis of Gibbs' phase rule it is concluded that it is, in its conventional form, strictly valid only in the absence of gravity. It is shown that for highly dilute microemulsion systems the density difference between water and oil can, even in the normal gravitational field of the earth, give rise to non -negligible energy terms. As a consequence the oil-water ratio varies with height in a normal test- tube. This opens the possibility to observe four or more phases at equilibrium in a three- component system at given temperature and pressure.