SEDIMENTATION BEHAVIOR AND COLLOIDAL PROPERTIES OF POROUS, CHEMICALLY-MODIFIED SILICAS IN NONAQUEOUS SOLVENTS

The sedimentation behaviour and colloidal properties of porous, chemic ally modified silicas dispersed in nonaqueous solvents have been studi ed. The free settling behaviour of non-aggregated silica suspensions c ould effectively be described with a modified Stokes equation that tak es into account the possible inclusion of gas in the pores of the part icles. The effects of hindered settling and of the dimensions of the s edimentation 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 mod ified silica particles. The electrophoretic mobilities of the particle s 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 po rous silicas. However, the way in which the particle suspensions are p repared determines whether the particles remain in the primary minimum or are colloidally stable. The level of gas entrainment provides info rmation on the homogeneity of the particle coating. (C) 1997 Elsevier Science B.V.