Effect of molecular weight and its distribution on the spinodal for polydisperse polymer solutions

The Flory-Huggins interaction parameter χ(ri) is considered as dependent on the chain length of a polymer. Therefore, a modified free energy expression of Flory-Huggins theory is obtained for the polydisperse polymer solutions. Based on this modified free energy expression and the thermodynamics of Gibbs, the expression of spinodal for polydisperse polymer solutions is obtained. For a given χ(ri) according to de Gennes, the spinodals are calculated for polydisperse polymer solutions at different molecular weights and their distributions. It is found that all the interested variables rn, rw, rz and molecular weight distribution have an effect on the spinodal for polydisperse polymer solutions, where the effect of changing rw is much greater than that of changing rn, rz and molecular weight distribution.