Peering into the Self-Assembly of Surfactant Templated Thin-Film Silica Mesophases

Citations Over TimeTop 10% of 2003 papers

Abstract

It is now recognized that self-assembly is a powerful synthetic approach to the fabrication of nanostructures with feature sizes smaller than achievable with state of the art lithography and with a complexity approaching that of biological systems. For example, recent research has shown that silica/surfactant self-assembly combined with evaporation (so-called evaporation induced self-assembly EISA) can direct the formation of porous and composite thin-film mesostructures characterized by precise periodic arrangements of inorganic and organic constituents on the 1-50-nm scale. Despite the potential utility of these films for a diverse range of applications such as sensors, membranes, catalysts, waveguides, lasers, nano-fluidic systems, and low dielectric constant (so-called low k) insulators, the mechanism of EISA is not yet completely understood. Here, using time-resolved grazing incidence small-angle X-ray scattering (GISAXS) combined with gravimetric analysis and infrared spectroscopy, we structurally and compositionally characterize in situ the evaporation induced self-assembly of a homogeneous silica/surfactant/solvent solution into a highly ordered surfactant-templated mesostructure. Using CTAB (cetyltrimethylammonium bromide) as the structure-directing surfactant, a two-dimensional (2-D) hexagonal thin-film mesophase (p6mm) with cylinder axes oriented parallel to the substrate surface forms from an incipient lamellar mesophase through a correlated micellar intermediate. Comparison with the corresponding CTAB/water/alcohol system (prepared without silica) shows that, for acidic conditions in which the siloxane condensation rate is minimized, the hydrophilic and nonvolatile silicic acid components replace water maintaining a fluidlike state that avoids kinetic barriers to self-assembly.

Related Papers

• → In-situ monitoring for mesophase formation processes of various pitches by means of high-temperature 13C-NMR(1991)21 cited
• → Chemistry and development of mesophase in pitch(1984)20 cited
• → A Method for the Determination of Mesophase Contents in Mesophase Pitch by Image Analysis(1993)
• → Quantitative analysis on carbonaceous mesophase from fused-state 13C-NMR spectra^|^mdash;Molecular structure, orientation and fluctuations of the constituents^|^mdash;(2012)
• Formation Behavior of Bulk Mesophase Pitch(1988)