| Abstract
| - The double-gyroid phase of nanoporous silica films formed by evaporation-induced self-assembly (EISA) has beenshown to possess facile mass-transport properties and may be used as a robust template for the nanofabrication ofmetal and semiconductor nanostructures. Recently, we developed a new synthesis of double-gyroid nanoporous silicafilms where the aging time of the coating solution prior to EISA was the key parameter required to control the interfacialcurvature that results upon self-assembly of the film. Here, we use 29Si nuclear magnetic resonance (NMR) andsmall-angle X-ray scattering (SAXS) to investigate the nanoscale structure of the coating solutions used to obtaindouble-gyroid nanoporous silica films. NMR and SAXS were carried out on the water, ethanol, silica, and poly(ethylene oxide)-b-poly(propylene oxide)-b-alkyl (EO17-PO12-C14) surfactant coating solutions as well as similarsolutions that excluded either the silica or the surfactant. NMR data reveal that the silica monomers in the coatingsolution condense very rapidly to form rings and connected ring species. After 1 day of aging, all monomers and dimershave disappeared, and the distribution is dominated by Q2 and Q3 species, where the superscript in Qn describes thenumber of silicon atoms in the second coordination shell of the central silicon. Over the course of the next 9 days,the Q3 population slowly rises at the expense of the Q2 and Q3t populations. Absolute intensity SAXS measurementsreveal that the size of the silica clusters increases steadily during this aging period, reaching an average radius ofgyration of 9.0 Å after 9 days of aging. Longer aging results in the continued growth of clusters with a mass fractaldimension of 1.8. Absolute intensity SAXS data also reveals that micelles are not present in the coating solution. At9% volume fraction of surfactant, the coating solution is far above the aqueous critical micellar concentration. However,even a small amount of ethanol inhibits micellization. SAXS data also shows that when surfactant is present the radiusof gyration is larger but increases more slowly. This indicates that there are weak associative interactions betweenthe silica clusters and surfactant in solution that reduce the cluster−cluster growth rate. In part II of this work, weuse the results discovered here to interpret the effects of aging on interfacial curvature in the nanostructured filmsthat self-assemble from these solutions.
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