Fourier transform infrared spectroscopic study of the adsorption of multiple amino silane coupling agents on glass surfaces

Abstract

The molecular structures of multiple amino coupling agents have been studied on glass surfaces and as solids using Fourier transform infrared spectroscopy. High specific surface area fumed silica (Cab-O-Sil) was used. N-2-Aminoethyl-3-aminopropyltrimethoxysilane (AAPS) and trimethoxysilylpropyldiethylenetriamine (TPDT) were deposited on glass surfaces from diluted aqueous and nonaqueous solutions. From toluene solution, the hydrolyzed AAPS was adsorbed onto glass surfaces to form a completely cured coupling agent layer. From aqueous solutions, the AAPS was deposited as an incompletely cured polyaminosiloxane. The band at 940 cm −1 is assigned to the SiO stretching mode of the uncured silanols of polyaminosiloxane. The difference spectra before and after heat treatment of these samples show the disappearance of the SiOH group of coupling agent and the glass surfaces. A model of interpreting the orientation of AAPS and TPDT on the surface of silica is proposed. The infrared integrated absorbance measurements of the amount of the AAPS and TPDT on the silica suggest that the amount of adsorption depends on the concentration of solution and the nature of coupling agents. The effects of hydrogen bonding and orientation on the adsorption mechanism are discussed. The hydrothermal stability of the coupling agents on the glass surfaces are also examined by infrared spectroscopy.