Fragmentation and Adhesion of Thin Metal Oxide Coatings on Polymer Films [Elektronisk resurs]

• This paper analyses adhesive and cohesive properties of nanometer thin coatings deposited by atomic layer deposition (ALD) on polymer film. Such coatings have excellent barrier properties as well as transparency [1], where the main application of the tested films for this present work is in food packaging. The materials of the coatings are TiO2 (titanium oxide)and MOX (mixed oxide, TiO2 and Al2O3). This experiment is carried out with four sample thicknesses; 20 nm for both coatings, 4 nm for the thin MOX coating and 6 nm for the thin TiO2. Fragmentation tests were performed using a tabletop scanning electron microscope (SEM) and an in-situ tensile stage for tracking the multiple cracking throughout the samples during increasing tension. That experiment allows to identify the nominal strain when the first flaw appear (crack onset strain), and also the point when no more cracks appear (crack saturation strain). The metal oxide coatings are non-conductive, and an additional conductive coating Au-Pd [2] is needed to be applied in order to perceive the cracks in the SEM. Although the conductive coating had approximately the same thickness as the brittle metal oxide coating, it was fortunately found that the relatively soft conductive coating had negligible influence on the cracking process. In-situ SEM testing has been shown to be a relatively straightforward method to quantify the coating cracking process, despite the small dimensions of the layer thickness and the crack openings. Furthermore, the Young’s modulus for each coating thickness was identified by nanoindentation, and comparison with FEM simulations of the load-displacement curve. The Young’s modulus is an important material property of the coating, it is also needed to estimate the interfacial shear strength at the interface between the coating and the polymer substrate at the crack saturation point [3]. The principles of the fragmentation tests are shown in, Figure 1. From the plots of the crack density versus nominal strain where, it is possible identify distribution in strain to failure of the brittle coating, as well as the limit of adhesion of the coating-substrate interface. The method will be exemplified and key material properties of some novel coating materials will be shown in the presentation. 

Ämnesord

Engineering and Technology  (hsv)

Nano Technology  (hsv)

Teknik och teknologier  (hsv)

Nanoteknik  (hsv)

Indexterm och SAB-rubrik

Thin coating

fragmentation test

cohesive failure

adhesive failure.