Tracking the fate of γ-aminopropyltriethoxysilane from the sol state to the dried film state

In this work, 29Si nuclear magnetic resonance and Fourier-transformed infrared spectroscopy were combined to study the hydrolysis and polycondensation of γ-aminopropyltriethoxysilane (γ-APS), both in the liquid sol state and in the film state. γ-APS sols were prepared in methanol or ethanol solvent in the pH range from 5.7 to 11 and deposited. The aim of the present study was to get the most complete picture in regard to the chemical events and time scale of these events. Transesterification reactions between γ-APS and methanol result in faster kinetics in methanol compared to ethanol. γ-APS films were deposited on aluminium and dried at ambient conditions (23 °C, 55% relative humidity). The silane films reached a chemical equilibrium in a couple of minutes (natural pH of 11) to 1 h (pH 7) depending on the pH of the silane solution. From a practical perspective, the results obtained here might give some clues to define an optimized schedule for the application of γ-APS coupling agent to metals.