| Abstract
| - The double-gyroid phase of nanoporous silica films has been shown to possess facile mass-transport properties andmay be used as a mold to fabricate a variety of highly ordered inverse double-gyroid metal and semiconductor films.This phase exists only over a very small region of the binary phase diagram for most surfactants, and it has been verydifficult to synthesize metal oxide films with this structure by evaporation-induced self-assembly (EISA). Here, weshow the interplay of the key parameters needed to synthesize these structures reproducibly and show that the interfacialcurvature may be systematically controlled. Grazing angle of incidence small-angle X-ray scattering (GISAXS) is usedto determine the structure and orientation of nanostructured silica films formed by EISA from dilute silica/(poly(ethylene oxide)-b-poly(propylene oxide)-b-alkyl) surfactant solutions. Four different highly ordered film structuresare observed by changing only the concentration of the surfactant, the relative humidity during dip-coating, and theaging time of the solution prior to coating. The highly ordered films progress from rhombohedral (R3̄m) to 2Drectangular (c2m) to double-gyroid (distorted Ia3̄d) to lamellar systematically as interfacial curvature decreases. Underall experimental conditions investigated, increasing the aging time of the coating solution was found to decrease theinterfacial curvature. In particular, this parameter was critical to being able to synthesize highly ordered, pure-phasedouble-gyroid films. The key role of the aging time is shown via processing diagrams that map out the interplaybetween the aging time, composition, and relative humidity. 29Si nuclear magnetic resonance (NMR) spectroscopyand solution-phase small-angle X-ray scattering (SAXS) of the aged coating solutions presented in part I of this seriesare then used to interpret the effects of aging prior to dip-coating. Specifically, it was found that a predictive modelbased on volume fractions and the silica cluster stoichiometry obtained from 29Si NMR qualitatively explains the trendsobserved with composition and aging. However, apart from the effects of relative humidity, a quantitative comparisonof the predicted phase with the experimental processing diagram suggests that less-condensed silica clusters are moreeffective at swelling the EO blocks at early aging times. This enhanced swelling decreases with aging time and resultsin lower-curvature nanostructures such as the double-gyroid. The decrease in swelling is attributed to the decreasedthermodynamic driving force for the more-condensed silica clusters to mix with the EO block of the surfactant.
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