Flory-Huggins parameter enthalpic 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... 

Experimental methods for determining the solubility parameter of a polymer are usually based on determining the Flory-Huggins polymer-solvent interaction parameter, X = Xh + Xs> and/or its enthalpic part Xh- The underlying theories will not be discussed here and the reader is referred to the books by Barton [ 1990B AR1, 1991BAR1],... 

The enthalpy of mixing per unit volume is directly related to the enthalpic part, of the Flory-Huggins polymer-solvent interaction parameter and so is the difference of the solubility parameters of polymer... 

All particularities of a certain real system (except for the chain length of the polymer) are incorporated into the third term, the residual Gibbs energy of mixing, and were initially considered to be of enthalpic origin. The essential parameter of this part is g, the integral Flory-Huggins interaction parameter ... 

In cases where the contact energy is temperature-independent, the entropy of mixing is purely combinatorial, i.e. it is expressed by the first two terms in eq. (4.48) and the third term in the Flory-Huggins equation is only enthalpic. Osmometry data from Schulz and Doll (1952) treated according to eq. (4.45) showed that the entropy part of the interaction parameter was significantly larger than the enthalpic part for solutions of polymethylmethacrylate in various solvents, e.g. for toluene as solvent at 20°C Xhu 0.03 and Xsu 0.42. 

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