Basic Principles of Thermodynamics of Polymer Solutions
At constant temperature and pressure, the dissolution is a spontaneous process proceeding in the direction of diminishing Gibbs free energy of mixing. The theories were proposed independently by P. J. Flory and M. L. Huggins, who developed the principles of the statistical thermodynamics of polymer solutions. The polymer molecules in solution, which are the chains constructed of the same chemical units, are characterized, in many cases, by the same interactions as the molecules of low molecular weight solvent. To calculate the entropy of mixing, Flory has used the lattice model of liquid. This model was modified for polymer solution in such a way that the polymer molecule occupied the row of adjacent cells in the lattice, whereas the solvent molecule occupies only one cell. By the quenching the solution of non-crystallizable polymer, one can reach temperature at which the solution separates into two phases: one enriched with polymer and the second is dilute solution.