The sedimentation behaviour and colloidal properties of porous, chemically modified silicas dispersed in non-aqueous solvents have been studied. The free settling behaviour of non-aggregated silica suspensions could effectively be described with a modified Stokes equation that takes into account the possible inclusion of gas in the pores of the particles. The effects of hindered settling and of the dimensions of the sedimentation vessel on the rate of sedimentation were investigated too. The colloidal properties of the silica particles were compared with predictions by the DLVO theory. The Hamaker and Lifshitz theories were utilized to describe the attraction forces between the chemically modified silica particles. The electrophoretic mobilities of the particles in the non-aqueous liquids were determined in order to quantify the electrostatic repulsion forces. The electrostatic repulsion appears to generate a large barrier against coagulation with all investigated porous silicas. However, the way in the particle suspensions are prepared determines whether the particles remain in the primary minimum or are colloidally stable. The level of gas entrainment provides information on the homogeneity of the particle coating.
|Colloids and Surfaces A: Physicochemical and Engineering Aspects
|Published - 1997