Flory-Huggins Theory Entropy of Mixing

The dissolution of a polymer in a solvent can be regarded as a two-stage process. The polymer exists initially in the solid state in which it is restricted to only one of the many conformations that are available to it as a free isolated molecule. On passing 

The formalism of the lattice was used for convenience to calculate the combinatorial entropy of mixing according to the method outlined in Section 8.2 for small molecules, including the same starting assumptions and restrictions. 

the number of vacant cells left, which can accommodate the next (/ -I-1) molecule, is given by 

FIGURE 8.1 Placement of polymer chains and solvent molecules on a lattice as required 

This gives the set of possible ways in which the (/ + 1) molecule can be accommodated on the lattice. The total nnmber of ways for all Afj molecules to be placed can then be obtained from the prodnct of all possible ways, i.e.. 

---