Dy. Kwok et al., FOWKES SURFACE-TENSION COMPONENT APPROACH REVISITED, Colloids and surfaces. A, Physicochemical and engineering aspects, 89(2-3), 1994, pp. 181-191
By comparing the number of degrees of freedom obtained from the phase
rule for capillary systems, the Fowkes surface tension component appro
ach for interfacial tensions is shown to require more degrees of freed
om than are available for a two-component solid-liquid-vapour system.
Only in a special case has the Fowkes approach two degrees of freedom:
a dispersive liquid on a dispersive solid, suggesting that there are
no surface tension components. Experimental results suggest that the F
owkes component approach does not describe physical reality; only the
liquid and solid surface tension, gamma(lv) and gamma(sv), are operati
ve in the two-component solid-liquid-vapour system. Generalization of
the Fowkes component approach, of course, will increase the number of
independent variables and hence definitely require more degrees of fre
edom than are avaialble. The number of degrees of freedom of the equat
ion of state for interfacial tensions is shown to agree with that pred
icted from the phase rule for capillary systems as well as with experi
mental results. By using the empirical form of the equation of state,
essentially constant solid tensions, gamma(sv), are obtained from a va
riety of dispersive and non-dispersive liquids for three solid surface
s: fluorocarbon (FC721), Teflon (FEP) and poly(ethylene terephthalate)
(PET).