Continuous model and Flory-Huggins theory

The continuous model can be treated very much like the lattice model. In this case, we write 

The first two terms in F correspond to the two-body and three-body interactions the third term represents the entropy of the system and would be equal to the entropy if the chains were not interacting with one another (for a perfect gas we have vt = (2/7/fft2/m)3/2e-1). 

The osmotic pressure II and the chemical potential n can be immediately deduced from (14.5.9) where F/V is considered as a function of C 

Then the demixtion curve is calculated exactly as in the general case. The result can be obtained by using the correspondence (14.5.10). Thus, using the definition ip = NCv we get 

By using (14.5.6), we can thus represent the demixtion curve in terms of the variables of the continuous model (see Fig. 14.16). 

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