PHASE-DIAGRAMS FOR BLOCK COPOLYMER HOMOPOLYMER BLENDS

A method is proposed for predicting the phase behaviors of blends of homopolymer A with block copolymer A-B. We assume that the mixtures are divided into two distinct states depending on their concentration and temperature. One state is a mesophase having ordered microdomains of the block copolymer, while the other is a liquid phase which consists of the disordered block copolymer and the homopolymer. On the assumption that the block copolymer in the liquid phase acts as a random copolymer, the free energy of mixing for the phase is evaluated by simply applying the Flory-Huggins equation to it. The free energy of mixing for the mesophase can be estimated by modifying the confined chain model originated by Meier. Then the relative stabilities of the two states, the mesophase and the liquid phase, are compared at various temperatures in order to construct a phase diagram. Consequently, by this method, we can obtain the composition-temperature phase diagrams for A/A-B blends, which are consistent with the results of previous experimental investigations.