We predict a diblock copolymer melt in the lamellar phase with added
spherical nanoparticles that have an affinity for one block to have a lower
tensile modulus than a pure diblock copolymer system. This weakening is due to
the swelling of the lamellar domain by nanoparticles and the displacement of
polymer by elastically inert fillers. Despite the overall decrease in the
tensile modulus of a polydomain sample, the shear modulus for a single domain
increases dramatically