| Abstract
| - Fluorinated surfactants are a special class of surfactants that assemble into aggregates and form novelintermediate mesophases more easily than hydrocarbon surfactants. Despite their unique properties,researchers have only recently begun to explore the use of these surfactants as templates for porousinorganic materials. Here, we report a comprehensive investigation of the use of cationic fluorinatedsurfactants as templates for ordered nanoporous silica. A homologous series of perfluoroalkylpyridiniumchloride surfactants with tail lengths between 6 and 12 carbons is synthesized and characterized. Usingthese surfactants in aqueous solution, materials are synthesized with pore structures that, as the tail lengthof the surfactant increases, include uniform wormhole-like pores, ordered 2-D hexagonal pores, and meshphase pores. The smallest pore diameter observed in this series (2.19 nm by the KJS method) is amongthe smallest observed for a porous ceramic made with a single chain cationic surfactant. To avoid initialimmiscibility of the silica precursor, a series of materials is also prepared from aqueous ethanol usingthe same series of surfactants. The products in this series include spherical particles with wormhole-likepores, spherical particles with radially oriented close-packed cylindrical pores, flower-like particles withradially oriented slit pores, and holey sheets of silica. For materials prepared in both water and in aqueousethanol we find, as has been observed for hydrocarbon templates, that the pore sizes increase as the taillength of the surfactant increases, as long as the pore architecture remains the same. Unlike materialsprepared with hydrocarbon surfactants, the pore architecture rapidly evolves toward mesh-phase andbilayer structures as the chain length increases. These investigations show that cationic fluorinatedsurfactants have significant potential not only as templates for controlling the size of familiar pore structuressuch as close-packed cylinders but also for developing ceramic materials with novel pore architecture.
- Homologous series of fluorinated pyridinium chlorides is synthesized, and these surfactants are used as supramolecular pore templates for a series of nanoporous silica particles. As the fluorocarbon chain length increases, the pores not only increase in size but also change shape from cylindrical to slitlike in some samples.
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