UPThèses

The Ph.D. work objective was the measurements of the mechanical properties of polymer foils and metal coated polymers, in connection with their microstructures. Two similar micro-tensile deformation devices were developed, which differ by their original non-contact deformation measurement techniques that are electronic speckle pattern interferometry and optical mark-tracking, at the Universities of Kaunas and Poitiers, respectively. The elongation range of both equipments allows for the investigation of elastic and plastic properties of polymer foils, coated polymer foils with thin metallic films. The substrates were either Kapton(r) HN or PET foils that were coated by electron beam evaporation with Al, Ag, Cr and Ni 0.5 thick thin films on both sides. The Young's moduli of the metallic thin films (Ef) were deduced from the stress-strain curves of the substrates and of the metallic/substrate composites. For Al and Ag, the deduced Ef values are in good agreement with those of bulk materials (Eb), while the Ef values for Ni and Cr are found drastically smaller than those of Eb. It was however observed that the Al and Ag metallic layers were uniform, whereas Ni and Cr films were far less regular and exhibit cracks. The microstructures and metal/polymer interfaces were essentially studied on the Ag/PET system. The influence of metal coverage on interface composition, structure, morphology and particle size has been studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). In addition, the role of deposition temperature over the temperature range 20°C-140°C, i.e. below and above Tg (Tg = 80°C is the PET glass transition temperature), was also examined to understand how microstructure, residual stress, chemical composition and morphology of the Ag/PET layer structure is affected. It was observed that Ag 1 μm thick films evaporated at different temperatures show a compressive stress state with either a (111) texture component below Tg or a random grain orientation above Tg. The texture is formed at the very early stage of growth, at a thickness of nearly 20 nm where the Ag film is still discontinuous. Within the investigated temperature range, the Ag grain size does not depend on the deposition temperature and the deposited films are mostly composed of pure Ag with partially oxidized surface.