1961/01/01 by J. S. Rowlinson, P. I. Freeman, Pauline Freeman
Engineering · Chemical Engineering · #Phase Equilibria and Thermodynamics #Thermodynamic properties of mixtures #Field-Flow Fractionation Techniques
paper · pdf · doi:10.1351/pac196102010329
I t is common for the mutual solubility of a pair of liquids to increase with temperature until miscibility is complete at a critical solution point. Per-haps the best known systems of this kind are mixtures of hydrocarbons with polar liquids such as aniline and nitrobenzene, in which the upper critical solution temperature (V.C.S.T.) is often used as a check on the identity and purity of the hydrocarbons. The explanation of this phase behaviour is simple. The mean energy of interaction ofa pair ofmolecules of one of the pure components is large because of their polarity. It is therefore energeti-cally difficult to dilute such a liquid with a non-polar one. As the tempera-ture is raised, considerations of energy become less important, and those of entropy become more important. Thus the miscibility increases with temperature. There are, however, a few systems in which the mutual solubility decreases with rising temperature and which are completely miscible only below a lower critical solution temperature (L.C.S.T.). Such systems are strongly hydrogen-bonded and, almost always, water is one of the