Compositional and orientational ordering in rod - coil diblock copolymer melts

The phase behavior of a melt of monodisperse rod-coil diblocks is studied. We derive a Landau free energy functional for both a compositional and a nematic order parameter. The excluded volume interaction between the rod blocks is modeled by an attractive Maier-Saupe interaction. The incompatibility between rodand coil blocks is modeled by the usual Flory-Huggins interaction. For large volume fraction of the rods a transition from isotropic to nematic to smectic C is observed upon decreasing the temperature, whereas for small rod volume fraction, spherical, hexagonal and lamellar structures prevail. In the smectic C phase the rod orientation angle with respect to the lamellar normal increases rapidly from 35 − 40o close to nematic/smectic-C phase boundary to values between 45 and 55o.