ADSORPTION OF (GAMMA-AMINOPROPYL)TRIETHOXYSILANE ON SILICA FROM AQUEOUS-SOLUTION - A MICROCALORIMETRIC STUDY

Adsorption of (gamma-aminopropyl)triethoxysilane (APS) on silica from aqueous solution was studied in situ by determining the differential e nthalpies of displacement (microcalorimetry) and the adsorption isothe rms (chromatographic type procedure). It is shown that, in the low con centration range (less than 0.2% in weight), the ethanol produced from the hydrolysis of the silane is not adsorbed whereas silanetriol (the other product of the hydrolysis) does not form polycondensates. The m ajor role of the amino function in adsorption is demonstrated by the s imilar behavior of APS and of a much Simpler aminated molecule, i.e. p ropylamine. This similarity is seen from both the microcalorimetric re sults and the influence of pH on adsorption. Nevertheless, the partial irreversibility of APS adsorption (evidenced here by liquid flow micr ocalorimetry and not observed for propylamine) seems to show and measu re the role of siloxane bonds in the adsorption of APS on silica.