Characterization of fumed silicas and their interaction with water and dissolved proteins

Fumed silicas synthesised with varied amounts of reactants (SiCl4, O2, H2) at the flame temperature of 1100–1400°C were studied using adsorption, infrared (IR), 1H NMR, dielectric relaxation (DRS) and photon correlation spectroscopy methods. These samples possess different specific surface area (100–410 m2 g−1), concentration of silanols (2.4–4.8 μmol m−2), weakly (0.6–3.0.wt.%) and strongly (0.5–3.8 wt.%) bound water (in air). Elevating synthesis temperature and decrease in the amounts of hydrogen/oxygen in the flame reduce the size of primary particles and the hydration level of fumed silica surfaces. Changes in synthetic conditions impact the characteristics not only of silica powders (reflected in their IR, DRS and NMR spectra in air) but also of their aqueous suspensions and adsorption of dissolved polymers such as albumin and gelatin. Increase in the concentration of surface silanols with growing size of primary particles enhances protein adsorption in mg m−2 of the oxide surface.