Core-Shell Gyroid Morphology in a Poly(isoprene-block-styrene-block-dimethylsiloxane) Triblock Copolymer. In this work we report a new morphology in a poly(isoprene-block-styrene-block-dimethylsiloxane) ABC triblock copolymer. The most probable symmetry of the morphology (Ia3hd) was determined from two-dimensional SAXS measurements performed on a sample with long-range order induced by an oscillatory shear field. By comparing the predictions of self-consistent field theory with TEM and SAXS and SANS powder diffraction patterns, we deduced that the morphology is a core-shell gyroid comprised of two independent and triply periodic poly(dimethylsiloxane) networks encased in poly(styrene) shells and separated by a continuous poly-(isoprene) domain. Thus, this unique nanostructure divides space into five independent, three-dimensionally continuous domains. (Shefelbine, T. A.; Vigild, M. E.; Matsen, M. W.; Hajduk, D. A.; Hillmyer, M. A.; Cussler, E. L.; Bates, F. S. - Core-Shell Gyroid Morphology in a Poly(isoprene-block-styrene-block-dimethylsiloxane) Triblock Copolymer - J. Am. Chem. Soc. 1999, 121, 8457.)

(a) TEM image taken from an unstained thin section of the ISD triblock copolymer. Natural contrast renders the poly(dimethylsiloxane) (D) domains dark, while the poly(isoprene) (I) and poly(styrene) (S) domains appear white. The "wagon wheel" pattern is associated the two D networks arranged in a gyroid morphology. (b) TEM micrograph obtained from an OsO4 stained thin section of ISD. Staining selectively darkens the I domains relative to the gray D and white S domains.