Comparison of the techniques used to modify amorphous hydrated silicas

Two techniques were used to modify the surface of a hydrated silica. The new, 'wet' technique of silica surface modification involved a direct reaction of the modifying agent with the surface groups of the just-forming hydrated silica. Commercial silane coupling agents of Y(CH2)(n)Si(OR)(3) type were used as modifying substances. For comparison, the classical 'dry' modification of the silica, earlier precipitated from sodium metasilicate solution, was conducted in parallel. In order to compare effects of modification performed using either of the techniques, basic physicochemical analysis of products was conducted, supplemented by near infrared (NIR) spectroscopy, calorimetric analysis to estimate heats of immersion of silica surface, transmission electron microscopy (TEM) to evaluate surface morphology of the products and DLS technique to evaluate the presence of agglomerate and aggregate structures. The studies demonstrated that the newly developed 'wet' modification technique was useful in production of modified precipitated silicas with hydrophobic surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.