Synthesis of TiO<INF>2</INF> Nanoparticles Utilizing Hydrated Reverse Micelles in CO<INF>2</INF>

Titanium dioxide nanoparticles were produced by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) in the presence of reverse micelles formed in CO<INF>2</INF> with the surfactants ammonium carboxylate perfluoropolyether (PFPECOO^-+NH<INF>4</INF>) (Mw = 587) and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA). Based on dynamic light scattering measurements, the amorphous TiO<INF>2</INF> particles formed by injection of TTIP are larger than the reverse micelles, indicating surfactant reorganization. The size of the particles and the stability of dispersions in CO<INF>2</INF> were affected by the molar ratio of water to surfactant headgroup (w<INF>o</INF>), precursor concentration, and injection rate. The amorphous particle size did not change upon depressurization and redispersion in CO<INF>2</INF>. PDMAEMA-b-PFOMA provided greater stability against particle aggregation at higher reactant concentration compared with PFPECOO^-+NH<INF>4</INF>. The crystallite size after calcination, which was examined by X-ray diffraction and transmission electron microscopy, increased with w<INF>o</INF>.