An evaluation of the

Gibbs free energy of mixing can give quantitative information about the interaction between the components in a mixed monolayer, and the relative thermodynamic stabilities of the mixed and the pure monolayers can thus be investigated.

in general, the thermodynamics and the phase diagram of a ternary system become available by using the Gibbs free energy of mixing. The classical representation of the Gibbs free energy of mixing for the three-component system of PS, SM, and EVA is as follows:

monomer residues) of each polymer ([x.sub.2][N.sub.2] and [x.sub.3][N.sub.3] represent for PS and EVA) are approximately of the same size, the Gibbs free energy of mixing becomes:

The necessary thermodynamic condition for the miscibility of components is that the Gibbs free energy of mixing, [delta][G.sup.mix], must be negative.

As seen from this equation, the combinatorial entropy contribution is chain length dependent and thus, for high molecular weight polymers, it does not have an important effect on the Gibbs free energy of mixing. Therefore, to obtain a miscible mixture, the enthalpic contribution, i.e., the third term in Eq 1, must be negative; that is, only exothermic mixing can result in a miscible mixture (7, 8).

These observations are in agreement with theoretical predictions of the phase diagram under shear, based on the concept of a modified

Gibbs free energy of mixing. The TEM results concerning the morphology of the phase-separated blends are also discussed.