Microstructural Characterization of Polystyrene-block-poly(ethylene oxide)-Templated Silica Films with Cubic-Ordered Spherical Mesopores Bernd Smarsly, †,‡ George Xomeritakis,* ,† Kui Yu,* ,§ Nanguo Liu, † Hongyou Fan, § Roger A. Assink, § Celeste A. Drewien, § Wilhelm Ruland, | and C. Jeffrey Brinker †,§ Center for Microengineered Materials, Advanced Materials Laboratory, University of New Mexico, 1001 University Boulevard SE, Suite 100, Albuquerque, New Mexico 87106, Sandia National Laboratories, MS 1349, Albuquerque, New Mexico 87185, and Department of Chemistry and Centre of Materials Sciences, University of Marburg, D-35032 Marburg, Germany Received May 9, 2003. In Final Form: June 13, 2003 We report the synthesis and characterization of mesostructured thin silica films derived from methyltriethoxysilane (MTES) and/or tetraethyl orthosilicate (TEOS) silica precursors and polystyrene- block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers via the solvent evaporation-induced self-assembly (EISA) process. It is found that the meso- and microstructure of the calcined films consists of cubic-ordered arrays of spherical mesopores of 5-7 nm in diameter, interconnected with a small number (e4% by volume) of PEO-induced micropores of ∼1 nm in diameter, as determined by new experimental results of transmission electron microscopy, N2 sorption, gas permeation, and grazing incidence small-angle X-ray scattering studies. The present comprehensive study of these novel closed-pore films should provide a general methodology for microstructural characterization of other related porous films prepared by similar self- assembly processes. 1. Introduction Since their discovery by Mobil researchers in 1992, 1 mesoporous inorganic oxides prepared by supramolecular self-assembly have attracted a great interest both from a fundamental point of view as well as for potential applications as catalysts, sorbents, or low k dielectrics. 2,3 The preparation of such materials in the form of thin films has been studied extensively, in particular by Brinker and co-workers 4 and Grosso and co-workers, 5 by means of low-molecular weight surfactants as structure-directing agents through solvent evaporation-induced self-assembly (EISA). Recently, we reported on the preparation of meso- structured silica thin films with a large characteristic length scale by using a high molecular weight amphiphilic block copolymer, e.g., polystyrene-block-poly(ethylene oxide) (PS-b-PEO), as structure-directing agent. 6 It was shown that various mesostructures could be obtained including regular and inverted ones. The reported system is believed to be the first to use high glass transition temperature (T g ≈ 373 K), PS-based amphiphilic diblock copolymers to prepare mesostructured silica/amphiphile films with highly ordered mesophases through the EISA process. In our most recent publication, 6b we reported on the self-assembly and mesostructural characterization of hydrophobic silica films with cubic-ordered spherical mesopores, using the same PS-b-PEO copolymer as structure-directing agent and methyltriethoxysilane (MTES) as silica source. While this study elucidated the pore size, shape, and 3D arrangement of the mesopores, it provided only limited information about the micro- structure, porosity, and pore connectivity of the silica matrix surrounding the mesopores. Previous studies showed that siliceous materials in general could contain * Corresponding authors.G.X.: fax (505) 272-7336; e-mail xomerita@unm.edu. 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