On Binary Phase Diagrams with Circular Envelope Spinodals of Polymer Blends

Six different binary phase diagram types are idenitified in polymer blends using the theories discussed in the literature to explain miscibility. These are:

(i) LCST (ii) UCST (iii)LCST and UCST (iv) Circular Envelope- Concave and Convex (v) Hour-Glass Behavior (vi) Hyperbola

The equilibrium and stability criteria are derirved from free energy expressions with both the enthalpic and entropic contributions. Expressions for the interaction parameter and its dependence on temperature are obtained using Equation of State, EOS theories for polymer and polymer mixtures as described in the literature. Miscible, immiscible and partially miscible states are distinguished from each other. The spinodal and binodal curves obtained for typical parameters of the models that predict miscibility are shown in illustrations.