ABSTRACT
The adsorption of two silane coupling agents, γ-aminopropyltrimethoxysilane (APTMS) and octyltrimethoxysilane (OTMS) onto porous silica particles from toluene solution is investigated by determining adsorption isotherms. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used to confirm the consumption of the silanol groups. The orientation of the bi(double)functional silane is investigated by comparing the (Langmuir-type) adsorption isotherm of APTMS with that of the mono(single)functional OTMS. The amount adsorbed and the bond strength found is compared with previously reported adsorption data for Bronsted and Lewis acid-base active probe molecules. In order to describe the adsorption over the entire concentration range the adsorption of OTMS is analysed not only by the Langmuir-isotherm, but also by the Freundlich- and combined Henry-Langmuir adsorption isotherms. The adsorption of γ-aminopropyltriethoxysilane (APTES) from aqueous solutions onto E-glass fibers is investigated using the ζ-potential, the contact angle, DRIFTS and electron spectroscopy for chemical analysis (ESCA or XPS). It was found that the APTES adsorbs from toluene with its amine group bound to the silica surface. In aqueous solutions both the silane and amine groups may be bound to the E-glass fiber surface, depending on the pH. If APTES is added in excess of a monolayer it separates out as merely a mechanically bound siloxane polymer network around the fibers ith properties being different from the silanized E-glass.
