Formation of aminosilane-oxide interphases

The aim of this work is to understand the interactions and interphase formation mechanisms between a liquid aminosilane oligomer (γ -APS) and glass, steel or gold surfaces as a function of the pH of the liquid aminosilane. When basic liquid γ -APS (pH 11.4) is applied onto a gold coated substrate, no interphase is detected. Similarly, when liquid γ -APS controlled at pH 8 is applied onto steel or glass substrates and cured, properties are the same as the bulk ones. In contrast, when the liquid γ -APS (pH 11.4) is applied onto steel or glass substrates and cured, an interphase, with chemical, physical and mechanical properties quite different from those of the bulk oligomer, is created between the substrate and the oligomer. Using various analytical techniques (DSC, FTIR, ICP, SEM, AFM, nano-indentation and XPS) it was shown that the amino-silane chemically reacts with and dissolves the oxide or hydroxide layers. Then metallic ions diffuse through the organic layer to form a complex, assumed to be of coordination type with the amine function of the oligomer molecule. These organometallic complexes are insoluble at room temperature and crystallize in the form of sharp needles. The Young’s modulus of the resulting crystal is equal to approximately 5 GPa, i.e. over two orders of magnitude higher than that of the silane. In other words, these organometallic complexes act as a short fiber in a matrix.