Hexagonally patterned lamellar morphology in ABC triblock copolymer/aluminosilicate nanocomposites

X-ray scattering and electron microscopy were used to characterize the structure of poly(ethylene-alt-propylene-block-ethylene oxide-block-n-hexyl methacrylate) (PEP-b-PEO-b-PHMA) triblock copolymer/ aluminosilicate hybrid materials in which the volume fraction of the PEP end-block (0.09 <= f(PEP) <= 0.12) was much smaller than that of the PEO-aluminosilicate (0.28 <= f(PEO+aluminosilicate) <= 0.44) and PHMA (0.47 <= f(PHMA) <= 0.60) domains. These hybrid compounds formed a hexagonally patterned lamellar morphology in which the lamellae were aligned parallel to the material surface (lamellar repeat spacing = 33.0 +/- 3.3 nm, in-plane row spacing = 21.7 +/- 1.9 nm). Both the PHMA and PEO-aluminosilicate phases formed continuous, two-dimensional domains permitting individual sheets of the material to be isolated by dispersal in organic solvent. Within each sheet, the lamellar PEO-aluminosilicate domain was hexagonally patterned by an array of holes with lower aluminosilicate density. Since the enthalpy of mixing for the small PEP end-block and PEO-aluminosilicate phase is very large, the holes in the PEO-aluminosilicate sheet may correspond to micellar PEP domains forming either dimples in the surface of the sheet or pillars spanning the sheet as in the proposed pillared-lamellae morphology (Macromolecules 2001, 34, 6994-7008). These results suggest that the use of ABC copolymers as structure-directing agents may provide access to a wide range of morphologies.