Effect of Interparticle Interactions on Agglomeration and Sedimentation Rates of Colloidal Silica Microspheres.

Abstract

The sedimentation half-times ts of initially monodisperse dispersions of 750, 505, and 350 nm silica microspheres were measured in water, in ethanol, and in aqueous NaBr solutions of concentration cNaBr ranging from 50 to 1000 mM, where the particles may have formed clusters. In water and in ethanol, ts was about 8, 18, and 33 h for the 750, 505, and 350 nm particles, respectively. These values were the same as the ones predicted by Stokes’ law, suggesting that the particles were monodisperse and remained so during sedimentation; ts values remained the same with increasing particle weight fraction up to 0.03, indicating no hydrodynamic interactions. Three regions of NaBr concentrations with different settling behavior were found for each size. In region I or at lower cNaBr, the ts values were the same as at no salt conditions, implying that there was no significant agglomeration before particles settled. In region II, ts decreased with increasing cNaBr, suggesting that the agglomeration and sedimentation ...