Rheological behavior of hydrophobic fumed silica suspensions in aromatic dispersion media

ABSTRACT

The rheological behavior of hydrophobic fumed silica with hexadecyl chains dispersed in toluene, o-xylene, m-xylene, and p-xylene was investigated as a function of the silica concentration, in order to understand the mutual interactions between the hexadecyl chains and the different dispersion media in terms of their solubility parameters. The solvent parameters of toluene and o-xylene were slightly less than those of m- and p-xylene. The relative viscosity η_r at shear rates <10 s⁻¹ decreased following the relation η_r, irrespective of the dispersion medium, and beyond a shear rate of 10 s⁻¹, the suspensions in toluene and o-xylene showed shear thinning behavior, whereas those in m- and p-xylene exhibited a second nearly Newtonian flow. The small-amplitude oscillatory shear tests showed that all suspensions behaved as gel-like matter, and the dynamic moduli of the suspensions in toluene and o-xylene were larger than those of the suspensions in m- and p-xylene. The large-amplitude oscillatory shear tests showed that the reduced storage moduli and loss moduli of the suspensions in the respective dispersion media below the crossover strain were superimposed on the corresponding curves, irrespective of the silica concentration, whereas above the crossover strain they depended on silica concentration.

GRAPHICAL ABSTRACT

KEYWORDS:

• Aromatic dispersion media
• fumed silica
• large-amplitude oscillatory shear (LAOS)
• small-amplitude oscillatory shear (SAOS)
• solvent parameter