Rheological behavior of hydrophobic fumed silica suspensions in different alkanes

Rheological behavior of hydrophobic fumed silica with hexadecyl chains dispersed in three alkanes: octane, dodecane, and hexadecane, were investigated as a function of the silica concentration, in order to understand the mutual interactions between the hexadecyl chains and the different alkanes. From a results of transient shear stress and steady-state shear viscosity tests, we can report that aggregated structures of the suspensions in hexadecane were harder and more easily broken up under shear than those in octane and dodecane. Small amplitude oscillatory shear (SAOS) tests showed that all suspensions behaved as a gel-like matter. According to the fractal gel model, the suspension in hexadecane was classified as a transient gel, whereas the suspensions in octane and dodecane corresponded to a strong-link gel. However, the fractal dimensions of all suspensions were almost independent of the dispersion medium. Large amplitude oscillatory shear (LAOS) tests showed that the reduced storage and loss moduli of the suspensions in hexadecane were superimposed on the respective curves, irrespective of the silica concentration, whereas those in octane and dodecane strongly depended on the silica concentration. Such differences indicated that the former dispersion medium was better incorporated with the hexadecyl chains than the latter dispersion media.