Molecular and mesoscopic structures of transparent block copolymer-silica monoliths

N. A. Melosh, P. Lipic, F. S. Bates, F. Wudl, G. D. Stucky, G. H. Fredrickson, B. F. Chmelka

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268 Scopus citations

Abstract

Mesoscopically ordered, transparent silica-surfactant monoliths have been prepared using amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymer species to organize polymerizing silica networks. The block copolymer acts as a structure-directing agent, as the aqueous silica cations partition within the hydrophilic regions of the self-assembled system and associate preferentially with the PEO blocks. Subsequent polymerization of the silica precursor species under strongly acidic conditions (pH approx. 1) produces a densely cross-linked silica network that may be mesoscopically organized by the block copolymer species into composites with characteristics ordering length scales of > 10 nm. When this is accompanied by slow evaporation of the aqueous solvent, such composite mesostructures can be formed into transparent and crack-free monoliths (e.g., 2.5 cm diameter × 3 mm thick). Distributions and dynamics of the PEO and PPO copolymer blocks within the silica matrix were investigated in situ using 29Si{1H} and 13C{1H} two-dimensional solid-state heteronuclear correlation NMR techniques and 1H NMR relaxation measurements. Mesostructural ordering was determined by X-ray diffraction and transmission electron microscopy. The degree of microphase separation and the resulting mesostructure of bulk samples were found to depend strongly upon the concentration of block copolymer, with higher concentrations producing higher degrees of order.

Original languageEnglish (US)
Pages (from-to)4332-4342
Number of pages11
JournalMacromolecules
Volume32
Issue number13
DOIs
StatePublished - Jun 29 1999

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    Melosh, N. A., Lipic, P., Bates, F. S., Wudl, F., Stucky, G. D., Fredrickson, G. H., & Chmelka, B. F. (1999). Molecular and mesoscopic structures of transparent block copolymer-silica monoliths. Macromolecules, 32(13), 4332-4342. https://doi.org/10.1021/ma9817323