Salted mesostructures: salt-liquid crystal templating of lithium triflate-oligo(ethylene oxide) surfactant-mesoporous silica nanocomposite films and monoliths

Abstract

A lyotropic lithium triflate-silicate liquid crystal is utilized as a supramolecular template for a ‘one-pot’ synthesis of a novel ionically conducting nanocomposite material, denoted meso-SiO₂-C₁₂(EO)₁₀OH-LiCF₃SO₃, in the form of a film or monolith. In this structure Li⁺ ions interact, in a crown ether-like fashion, with oligo(ethylene oxide) head groups of a non-ionic surfactant assembly that is imbibed within the channels of hexagonal mesoporous silica. Details of the acid catalyzed polymerization of the silicate oligo(ethylene oxide) surfactant co-assembly in the presence of lithium triflate have been investigated using polarized optical microscopy (POM), powder X-ray diffraction (PXRD), multinuclear nuclear magnetic resonance (NMR) spectroscopy and impedance spectroscopy. Insight into the incorporation of Li⁺ and CF₃SO₃^– ions into meso-SiO₂-C₁₂(EO)₁₀OH-LiCF₃SO₃ was obtained using NMR and Fourier transform (FT) Raman spectroscopy. Collectively the results indicate that lithium ions coordinate to oxygens of the oligo(ethylene oxide) head group, maintain the structural integrity of both the silicate liquid crystal and templated mesoporous silica, and are essentially completely dissociated with respect to the triflate counteranion. ac Impedance spectroscopy, which bodes well for their use in the fields of polymer electrolytes and battery technology for meso-SiO₂-C₁₂(EO)₁₀OH-LiCF₃SO₃ have demonstrated high ionic conductivities at room temperature measurements. Salt-liquid crystal templating may offer a general approach for synthesizing diverse kinds of salted mesostructures including redox active transition metal complexes, which may be reductively-agglomerated to form metal cluster-based meso-SiO₂-C₁₂(EO)₁₀OH-M_n or sulfided with H₂S to produce semiconductor cluster-based meso-SiO₂-C₁₂(EO)₁₀OH-(MS)_n nanocomposites.

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