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Morphology Evolution in Mesoporous Titania Block Copolymer Composite Films with Increasing Sol–Gel Reaction Time

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Abstract

A morphology evolution of thin films of titania from spherical mesopores to worm-shaped mesopores was realized by simply varying the sol–gel reaction time from 46 min to 25 h in the quadruple system consisting of polystyrene–block-poly(ethylene oxide) (PS–b-PEO), 1,4-dioxane, concentrated HCl, and titanium tetraisopropoxide (TTIP). Imaging techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to investigate the local structure change of the as-prepared, calcined, and UV-degraded composite films. Grazing incidence small angle X-ray scattering (GISAXS) experiments prove that the structure change in local areas is representative of that over the macroscopic scale. An X-ray reflectivity (XRR) investigation reveals that the vertical structure change happens when the sol–gel reaction is extended from 5 to 25 h. A combination of imaging and scattering techniques provides a powerful tool to elucidate the impact of the sol–gel reaction time on the morphology evolution of the composite films. Dynamic light scattering (DLS) studies imply that the morphology evolution within the films is due to the structure change in solution. A mechanism of the morphology evolution with sol–gel reaction time is proposed on the basis of these results, which provide not only a new way to control the morphology of titania block copolymer composite films but also deep insights into the kinetics of the amphiphilic block copolymer templating process.

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