Peter Fink

Investigation of quantitative SiOH determination by the silane treatment of disperse silica

Abstract The concentration of free silanol groups after treatment of disperse silica with 3-(trimethoxysilyl) propyl methacrylate (A-174) was studied in substance pellets by IR spectroscopy. There are significant structural differences between the silica which was treated with gaseous silane and that which was treated in solution. By gas-phase silanation a monolayer of methacrylate was formed, while in solution a polylayer was formed. This conclusion results from a determination of carbon content by means of elemental analysis in addition to an IR spectroscopic determination of the SiOH concentration remaining in the silane-treated silica surface. Silylation by means of hexamethyldisilazane was found to be a convenient method to determine the concentration of these residual silanol groups.

IR-spektroskopische Charakterisierung der Oberflächenkomplexe bei der Pyridinadsorption an chemisch modifiziertem SiO2 (Aerosil)

Various siliceous surfaces are characterized regarding some properties of their proton donating centers by the infrared spectra of adsorbed pyridine. These oxides are silica and silica containing oxides of Ge, Sn, Ti, Cr, , Al and as well as Cl and NH groups on the surface, respectively. In every system, there exist both a strong hydrogen bond between surface OH or NH groups and pyridine molecules and an infrared continuous absorption. Moreover, the adsorbents S1O2/P2O5 and Si02/Ala03 as well as chlorinated silica have BR0NSTED acid centers; the pyridine adsorption on these oxides is accompanied by the appearence of a broad, relatively weak band at about 2700 cm-1 which is assigned to the N+—H stretching vibration of the pyridinium ions. The results are discussed in terms of the acidity of the surface hydroxyls. The strongest acidity is shown by the OH groups of SÌO2/P2O5, and the weakest acidity by those of SÌO2/B2O3.