Demixtion curves and the Flory-Huggins approximation

The demixtion curves obtained experimentally (see Fig. 16.2) are in qualitative agreement with the theoretical predictions of Chapter 14. 

Let us discuss these results in a more quantitative manner by using the Flory-Huggins approximation. We examine in particular how the coordinates Te and pc of the top of the demixtion curve vary as functions of the equivalent Brownian area S of the chains. We can also replace the area S by the number N of links or the molecular mass M of the chain, all these quantities being proportional. 

Let us recall that the solute is as monodisperse as possible. We suppose that the polydispersion is characterized by the ratio 

The values of Te deduced from Fig. 16.3 and the other experimental values of Tc concerning the polystyrene-cyclohexane system obey the empirical relation 

The Flory-Huggins theory and the simple-tree approximation in the standard continuous model lead to formulae that are in both cases similar to (16.2.7), Let us consider the parameter ( — / ) of the Flory-Huggins theory (see Chapter 14, Section 5.3). The correspondence with the continuous model is given by (14.5.13) 

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