Dispersion of Phosphonic Acids Surface-Modified Titania Nanocrystals in Various Organic Solvents

Titanium dioxide (TiO2, anatase) nanocyrstals tha can be transparently (perfectly) dispersed in several organic solvents were synthesized by organic-ligand-assisted hydrothermal synthesis. To analyze the dispersion behavior of surface-modified nanocrystals from the surface of the surface-modified nanocrystals, three types of surface-modified TiO2 nanocrystals were prepared. Depending on the surface nature of the surface-modified Tila, nanocrystals, the nanocrystals showed different dispersion behaviors in organic solvents. In particular, the dispersion of surface-modified TiO2 nanocrystals with carboxylic acid terminated surface modifier (TiO2-COOH) varied strongly with changing solvent species. We investigated the dispersity of TiO2-COOH in typical organic solvents using dynamic light scattering (DLS) measurements. One of the three-dimensional solubility parameters, namely, the Hansen solubility parameter, provided detailed information on the mechanism of the dispersion of TiO2-COOH. Because of the carboxylic acid groups exhibited on the surface of the titania nanocrystals, the dispersion of TiO2-COOH was very much affected by the hydrogen-bonding ability of the solvent. The hydrogen-donating/-accepting ability adequately described the dispersion of TiO2-COOH in organic solvents.