Measurements and Correlation of Octyltriethoxysilane Solubility in Supercritical CO2 and Assembly of Functional Silane Monolayers on the Surface of Nanometric Particles

Trialkoxysilanes are widely used as primers to functionalize inorganic nanoparticles and to facilitate their interaction with organic phases. In this work, the silanization of nanometric fillers (titania and maghemite) was successfully carried out using supercritical carbon dioxide as the carrier solvent for octyltrialkoxysilane. First, the solubitility behavior of octyltriethoxysilane in compressed CO2 was evaluated at different pressures and temperatures. The measured solubility data were correlated using the Chrastil equation. Next, nanometric powders of either titania or maghemite were silanized at different pressures, temperatures, and reaction times. The prepared samples were characterized by electron microscopy, N-2 adsorption-desorption, and laser scattering. Finally, the operating conditions that led to optimal material performance as a function of the intended application for the coated titanium dioxide powder (UV filter in cosmetics and filler in plastics) were evaluated by means of conveniently defined objective functions.