Characterizing Chemically Reactive Thin Layers: Surface Reaction of [2-[4-(Chlorosulfonyl)phenyl]ethyl]trichlorosilane with Ammonia

Thin layers of organosilanes on oxidic surfaces are of great interest for various applications including the control of surface properties and immobilization of catalysts and biomolecules and in nanotechnology. In the present work, the reaction of thin layers on silicon oxide consisting of [2-[4-(chlorosulfonyl)phenyl]ethyl]trichlorosilane (CSTS) with ammonia is studied by means of contact angle (CA) measurements, ζ-potential measurements, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FT-IR). CA measurements are used for a fast monitoring of film quality and as a first probe for the reaction of the CSTS sample with ammonia. The results from XPS measurements show that the chlorine peak of the CSTS molecule disappears completely after the reaction with ammonia and instead a well-resolved nitrogen peak appears. FT-IR spectroscopy in conjunction with theoretical calculations is used to gain a more in-depth understanding of the chemical reaction. The shift of the asymmetric S O vibrational mode during the surface reaction is in line with the theoretical predictions and serves as a proof for the surface reaction to happen. By FT-IR, an additional side reaction of sulfonic acid groups, which are present in the commercial CSTS, to the ammonium sulfonate salt is observed.