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-SiO ₂ -C ₁₂ (EO) ₁₀ OH-LiCF ₃ SO ₃ , 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 CF ₃ SO ₃ ^– ions into meso-SiO ₂ -C ₁₂ (EO) ₁₀ OH-LiCF ₃ SO ₃ 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-SiO ₂ -C ₁₂ (EO) ₁₀ OH-LiCF ₃ SO ₃ 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-SiO ₂ -C ₁₂ (EO) ₁₀ OH-M _n or sulfided with H ₂ S to produce semiconductor cluster-based meso-SiO ₂ -C ₁₂ (EO) ₁₀ OH-(MS) _n nanocomposites.