Determination of structure-property relationships for 3-aminopropyltriethoxysilane films using x-ray reflectivity

Films of 3-aminopropyltriethoxysilane films (APTES) deposited from nonpolar solvents show unusual hardness and tribological properties. The morphological origin of this behavior is determined using x-ray reflectivity. The deposited APTES films are smooth, evolving from a sparse structure when less than two-molecule-thick (<1 g/cm3) to a dense structure (1.26 g/cm3) when thicker. Previously reported improvements in wear resistance and hardness are due to the unusually dense nature of the APTES film. The density of multilayered APTES film has implications for its use as an interface-coupling agent because the film density limits the reactivity of embedded amine groups. A high-temperature cure (120 °C) does not affect film density but does significantly improve hydrolytic stability. Given their high density, predictable reactivity, stability and resistance to wear, multilayered APTES films are well suited for interfacial modification designed to improve mechanical properties, provided the films are properly cured.