Surface segregation in thin films of symmetric polyolefin diblock copolymers containing a lamellar microstructure, cast on a variety of substrates, has been investigated. In all cases, the conformationally smaller block preferentially segregated to both the solid and air interfaces even though the surface energy of the solid substrate always exceeded that of the block copolymer. These results indicate an entropically driven surface segregation effect that we attribute to block conformational asymmetry.

• Received 17 June 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.307