Effect of Sol–Gel Reaction Time on the Morphology Transition in Mesoporous Titania/PS-<I>b</I>-PEO Composite Films

Abstract

A morphology transition from the coexistence of spherical and worm-like mesopores to highly branched wormlike mesopores within the titania thin films has been realized by varying the sol gel reaction time from 51 minutes to 50 hours in the four-component templating system of PS-b-PEO, 1,4-dioxane, concentrated HCl, and Titanium tetraisopropoxide (TTIP). The impact of sol gel reaction time on the local structure, long range lateral structure, and vertical structure of the as-prepared, calcined, and UV degraded thin films, and structure change in solution have been systematically investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR), and dynamic light scattering (DLS) respectively. With the sol gel reaction time up to 5 hours, the morphology does not change significantly. Both spherical and worm-like domains exist, which are converted to spherical and worm-like mesopores after calcination or UV degradation due to the removal of the PS block. However, with the sol gel reaction time extended to 25 and 50 hours, highly branched worm-like domains appear. As a result, highly porous mesopores are formed by calcination or UV degradation. The GISAXS results prove that the local structure change revealed by AFM and SEM is representative over macroscopic scale. X-ray reflectivity results indicate that an additional thin layer exists beneath the mesoporous titania layer due to the presence of large amount of worm-like domains. Dynamic light scattering (DLS) studies imply that the morphology transition is due to the fusion process of the worm-like micelles in solution.