Staverman correction

To obtain the complete activity coefficient, only the residual term from the UNIT AC model, Equation [4.4.87], has to be added. An attempt to incorporate differences in shape between solvent molecules and polymer segments was made by Kontogeorgis et al. by adding the Staverman correction term to obtain ... 

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... 

Parameters related to differences in size and shape and respectively change in internal energy of mixing Entropy correction terms Parameter related to average interaction energy Internal energy of the system Flory s equation of state Flory-Huggins Staverman theory... 

Staverman examined the problem of representing a solution in which the molecules are no longer linear, and therefore a certain amount of the molecule would not be exposed to the molecules of solvent, because they would be isolated inside the molecule of solute. These imprisoned sites receive no molecules of solvent. Figure 3.5 gives a 2D representation of the exclusion of certain sites (shaded) which are no longer able to receive molecules of solvent as near neighbors. This introduces a corrective factor relating to the surface of the molecule. 

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