PHASE-BEHAVIOR OF SEMIFLEXIBLE DIBLOCK COPOLYMERS

We examine the phase behavior of diblock copolymers of arbitrary flexi bility near their order-disorder transition. Our approach is based on a free energy functional calculated from a microscopic model of rigid rods connected with free joints and depends only on a small set of par ameters, including the Flory chi parameter, a Maier-Saupe parameter, a nd the rod lengths and molecular weights of each block. By analyzing s pinodals within this model, we have explored the effect of differences in flexibility between the two blocks, as well as the stiffness of th e diblock as a whole, on the phase behavior. We find that nematic and microphase fluctuations can significantly affect transition temperatur es and phase boundaries when the difference in stiffness is large.