Structural Analysis of Hybrid Titania-Based Mesostructured Composites

Abstract

High-optical-quality titania-based mesostructured films with cubic or 2D-hexagonal symmetry were fabricated by combining trifluoroacetate (TFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) copolymers. The distribution, dynamics, and local environments of the TFA-modified titania, PEO, and PPO components of the hybrid were investigated. IR/Raman spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy studies indicate that TFA coordinates the titanium center and forms a stable complex that is subsequently organized by the block copolymer species into ordered mesostructures. Solid-state NMR ¹⁹F→¹H cross-polarization, ¹³C{¹H} two-dimensional heteronuclear correlation, and ¹H relaxation techniques were used to determine that PEO is predominantly incorporated within the TFA-modified titania, and that PPO environments encompass both microphase separated regions and interfacial regions composed of mixed PPO and TFA-modified titania. NMR ¹⁹F multiple-quantum spin counting measurements suggest that −CF₃ groups of the trifluoroacetate ligands do not form clusters but instead randomly distribute within the inorganic component of the hybrid.