Combined TEM and XPS studies of metal - polymer interfaces for space applications

Abstract

The stability of metal-polymer interfaces after extreme thermal cycling is essential for high-performance thermal insulation of satellites. The Aluminium-Polyimide (Al-PI) system investigated here is used as a multilayer insulator for satellites currently in low earth orbit. Its interfacial adhesion should be resistant to thermal loading caused by the sun during orbit. In this study, transmission electron microscopy (TEM) is combined with X-ray photoelectron spectroscopy (XPS) to relate the interface structure and chemistry to the mechanical strength of the Al-PI interface as a function of thermal cycling. Results show that the interfacial properties of Al-PI remain unaffected by thermal cycling of ±150°C in gaseous nitrogen up to 200 thermal cycles. TEM cross-sections were used to examine the interface structure and revealed a 3.6nm, amorphous interlayer between Al and PI for as deposited and cycled samples. XPS survey scans and relevant high resolution core levels were recorded on both sides of the interface to identify and understand relevant interfacial bonding as well as to distinguish between adhesive failure at the interface and cohesive failure in the polyimide substrate. The Al-PI system presented in this study can serve as a model for strong and thermally resistant metal-polymer interfaces. The combination of interface strength, structure and chemistry allows for an improved understanding of how thermal treatments can influence interfacial behaviour between metals and polymers and will help improve design and reliability of materials used in space as well as terrestrial applications.