Flory-Huggins parameter entropic part

For more than two decades researchers have attempted to overcome the inadequacies of Flory s treatment in order to establish a model that will provide accurate predictions. Most of these research efforts can be grouped into two categories, i.e., attempts at corrections to the enthalpic or noncombinatorial part, and modifications to the entropic or combinatorial part of the Flory-Huggins theory. The more complex relationships derived by Huggins, Guggenheim, Stavermans, and others [53] required so many additional and poorly determined parameters that these approaches lack practical applications. A review of the more serious deficiencies... 

X°° Flory-Huggins interaction parameter at infinite dilution of the solvent Xs entropic part of x°° (is often set equal to 0.2-0.4)... 

The first term in braces represents the Landau-type free energy of crystal solidification of each component in which the individual free energy of the constituents is weighted by the respective volume fractions to ensure that these potentials vanish at the extreme limits of zero crystallinity or if a component is non-crystallizable. The second term represents the entropic part of the free energy of mixing of the amorphous constituents. In the third term, Xaa corresponds to the amorphous-amorphous interaction parameter of Flory-Huggins that characterizes the stability of the liquid phase. 

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