De‐agglomeration of Silica Nanoparticles in the Presence of Surfactants

Abstract

The effect of the type of surfactant and pH on de‐agglomeration of a hydrophilic silica nano‐powder in a high shear mixer was investigated. It has been found that the presence of surfactant does not affect the general pattern of de‐agglomeration characterized by the transition of a single modal aggregates size distribution with the median of 10 µm, through a bi‐modal distributions with the second median of the order of 100 nm to a single modal distribution with the median of the order of 100 nm. None of the investigated surfactants enabled de‐agglomeration of the nano‐powder into a primary nanoparticle. At pH=4, breakage of large secondary aggregates was enhanced by the addition of PEG and PVP, whereas the addition of SDS slowed down de‐agglomeration. The final aggregates were larger in all suspensions containing surfactant than in surfactant free suspensions. At pH=9 all surfactants drastically reduced de‐agglomeration rate without affecting the size of the primary aggregates. PEG induced bridge flocculation of the primary aggregates leading to a drastic change of the rheology of suspension.