Layer-by-Layer Assembly of Titania Nanosheet/Polycation Composite Films

Abstract

Unilamellar titania crystallites of Ti1-δO24δ- (δ = 0.0875) and polydiallyldimethylammonium chloride have been alternately deposited layer-by-layer onto various substrates from their aqueous media. An atomic force microscopy (AFM) image visualized the adsorbed nanosheets, which gave efficient coverage of the substrate surface. The resulting multilayer film apparently displayed a very intense UV absorption (ε = 2.2 × 104 mol-1 dm3 cm-1 at 265 nm) due to the titania nanosheets with a molecular thickness. X-ray diffraction (XRD) measurements detected a Bragg peak, which reflects a nanosheet/polycation nanostructure inside the film. Its multilayer repeat distance was 1.4−1.7 nm, being dependent on the surrounding humidity. Simulation on the XRD profile suggested that the obtained films have some structural disorder, involving about 20% of the mean displacement for the multilayer repeat spacing. Spectroscopic ellipsometry data can successfully be analyzed based on a multilayer assembly model composed of titania nanosheets that are ∼1.2 nm thick and polycations that are ∼0.7 nm thick, which is substantially compatible with the XRD and AFM data.