Solubility of titanium diisopropoxide bis(dipivaloylmethanate) complex in supercritical carbon dioxide and its effect on supercritical fluid deposition process

The solubility of a titanium (Ti) complex, titanium diisopropoxide bis(dipivaloylmethanate) [Ti(Oi-Pr)2(dpm)2], in supercritical carbon dioxide (scCO2) fluid was measured under various fluid temperatures and pressures to clarify its effect on supercritical fluid deposition (SCFD) for titanium dioxide (TiO2) films, by means of the extraction method with 2-propanol as the extracting solvent and UV–vis spectroscopic analysis. The solubility which is expressed by molar ratio of Ti complex to CO2, μ, decreased with the fluid temperature, Tf, from 40 to 60 °C, while it increased rapidly with the fluid pressure, Pf, from 6 to 10 MPa and then increased gradually with Pf from 10 to 20 MPa. The behavior was analyzed by Chrastil's equation model. The deposition rate of TiO2 films by SCFD was understood to be proportional to the difference in the mass concentration of Ti complex, S, between in the bulk transport medium and vicinity of the substrate surface.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlight► Solubility of titanium diisopropoxide bis(dipivaloylmethanate) in supercritical carbon dioxide fluid. ► Flow-type extraction apparatus for determining solubility of solid in supercritical carbon dioxide. ► Analysis of dissolution behavior of titanium diisopropoxide bis(dipivaloylmethanate) by empirical density-based Chrastil ‘s model. ► Supercritical fluid deposition of TiO2 film controlled by supersaturation of precursor in CO2 fluid.