When fumed silica is dispersed in a non-polar liquid, the silanol groups on the surface of different particles are bridged by hydrogen bonding and thickened by forming a three-dimensional structure. When this structure is subjected to mechanical external forces, such as agitation or shaking, the structure is destroyed. The type and duration of the mechanical external forces acting on it determine the extent of the damage. As a result, the thickened system becomes liquid again. If left standing, fumed silica particles will be connected again to restore the original viscosity. This phenomenon is called pseudoplasticity.
Fumed silica fume-thickened systems require a minimum amount of energy to start flowing, in other words, a so-called "yield point." Hydrophilic fumed silica has no obvious thickening effect on polar or semi-polar liquid. Surface-modified fumed silica shows up in these systems, especially in liquid mixtures or solutions.
