P. Fayet

Mechanical analysis of ultrathin oxide coatings on polymer substrates in-situ in a scanning electron microscope

Uniaxial fragmentation tests were carried out in situ in a scanning electron microscope (SEM) on 10-nm-thick silicon oxide coatings deposited by plasma enhanced chemical vapor deposition on poly(ethylene terephthalate). In order to prevent charging effects due to the isolating nature of the oxide surface, an additional conductive gold layer was sputtered onto the coating prior to its tensile loading in the SEM chamber. The gold layer was shown not to affect initiation of tensile failure of the oxide coating, and was used to achieve optimal resolution by eliminating charging effects in the low-strain range. In contrast, in the high strain range, the failure behavior of the oxide coating was found to be modified by the gold layer. It was nevertheless possible to analyze the damage mechanisms of the thin coating without a gold layer due to sufficient crack opening. The coating cohesive strength was found to be equal to 5.1 GPa, and the coating/polymer interfacial strength was found to be equal to 84 MPa using a Weibull size-dependent probability of failure for the oxide, and assuming a perfectly plastic stress transfer between the different layers.

Durability of hybrid PECVD-based coatings on semicrystalline polymers

The present work analyses silicon oxide coated polyester films, with attention paid to the effect of substrate process additives on the coating defect population, and on the coated film mechanical properties. The defect population is characterized by means of reactive ion etching, and the mechanical properties are determined from the analysis of uniaxial fragmentation tests. The coating crack onset strain is decreased by the presence of substrate additives, due to a broadening of the Weibull defect distribution. Moreover, finite element analysis of stress concentrations resulting from additive-induced roughness shows that local stress concentrations are negligible. It is the critical defects, such as microcracks that are the most detrimental to the coating effective cohesive properties.

Effect of substrate crystalline morphology on the adhesion of plasma enhanced chemical vapor deposited thin silicon oxide coatings on polyamide

The influence of the surface morphology of semicrystalline polyamide 12 (PA12) on the adhesion of thin silicon oxide coatings is analyzed by means of uniaxial fragmentation tests and scanning local-acceleration microscopy (SLAM). Two types of PA12 substrates are investigated, namely, as-received PA12, which contains large spherulites, and quenched PA12, which has a relatively smooth, homogeneous surface structure. The adhesion of the coating is found to be identical for the two types of PA12. This indicates that plasma deposition of the oxide leads to an equivalent functionalization of the two types of surfaces. Nonetheless, localized delamination is observed at spherulite boundaries, and is argued to result from strain concentrations in the corresponding soft zones, revealed by SLAM measurements.