theory is not known. A brief discussion of the physical properties
of fluorocarbon-hydrocarbon solutions and the possibility of using
spin-lattice relaxation measurements as a means of investigating their
unusual behavior is now presented.
The chief approach to the analysis of the thermodynamic prop-
erties of these solutions has been the regular solution theory first
proposed by Hildebrand and Scatchard [48]. Experimental data accumu-
lated after the first attempt by Scott [49] to apply the regular solu-
tion theory to fluorocarbon-hydrocarbon solutions was in disagreement
with that theory [50-57]
There have been various explanations of this unusual behavior.
Dunlap [51] proposed a mechanical model. The hydrocarbons, because of
their small size, could fit together like gears. Because of this close
approach, not possible for fluorocarbon-fluorocarbon or hydrocarbon-
fluorocarbon solutions, the hydrocarbon-hydrocarbon interaction energy
should be very large. Hildebrand [58] suggested that the solubility
parameters of hydrocarbons be arbitrarily increased. Dunlap [59] also
suggested that the large heats of mixing observed are a result of large
volume expansions, and corrections to constant volume would remove
most of the anomaly.
Another approach has been the application of corresponding
states theory [60]. A Lennard-Jones potential function is assumed,
and the excess free energy is calculated. The collision diameter is
taken to be the arithmetic mean of the diameters of the two inter-
acting molecules, and the potential energy function is taken to be the