Simultaneous aggregation and sedimentation of silica particles in the presence of surfactants

Simultaneous aggregation and sedimentation of silica particles in the presence of surfactants has been studied by performing experiments using Kruss tensiometer (K100). Experiments are based on the measurement of cumulative mass versus time, of the settled particles with the help of a highly precise weighing balance. The effects of various factors, such as, surfactant concentration, pH and salts have been studied in detail. The aggregation and sedimentation of silica particles in presence of HTAB surfactant is faster at HTAB concentration of 0.2 cmc and in the pH range of 8-10. The aggregation and sedimentation of silica particles increase in the presence of salts e g., CaCl2 and NaBr, due to screening of charges on silica particles. However, the presence of both HTAB and CaCl2 or NaBr has detrimental effect on aggregation and consequently sedimentation rate of silica particles is decreased. These results are explained based on hydrophobic and electrostatic interactions between silica particles and surfactant molecules.