Thermodynamic and micromechanical approaches to the adhesion between polyethylene terephthalate and silicon oxide

The adhesion between different types of polyethylene terephthalate (PET) su bstrates coated with thin silicon oxide (SiOx) layers is examined using two alternative approaches. The surface of the polymer was hydrolyzed or silyl ated prior to the deposition of the oxide layer, to be compared with untrea ted PET. The first approach is the thermodynamic adsorption model from whic h are defined the dispersive and polar components of the polymer surface en ergy, obtained from wetting measurements. The second approach is the microm echanical analysis of the interface stress transfer which provides the inte rface shear strength from the measurement of the density of coating cracks vs. applied tensile strain. The hydrolysis treatment slightly hydrophobizes the PET surface; however, it does not significantly modify the interface s hear strength compared with the untreated material. By contrast, the silane treatment improves the polar component of the PET, which is related, to a first approximation, to the measured 30% increase of the interface shear st rength compared to the untreated material.