Adhesion of latex films. Part II. Loci of failure

In order to continue our work on surfactant effects on the adhesion properties of latex films, we investigated a new system based on an acrylic copolymer, synthesized in the presence of a hydrophilic polyester. The surfactants were either sodium dodecyl sulfate (SDS) or an ethoxylated nonyl phenol containing 30 ethoxy groups (NP30). As substrates, either glass plates or poly(ethylene terephthalate) (PET) films were used. This article describes the analysis of the loci of failure after peeling of the films. The analytical techniques used were X-ray photoelectron spectroscopy (XPS) (or ESCA), static secondary ion mass spectrometry (SSIMS), and contact angle measurements. It was shown that the loci of failure were independent of the peel rate and of the nature of the substrate. The failure occurs in a thick surfactant layer for SDS, and in a thin one for NP30. The thickness of the layer increases with the concentration of surfactant in the latex film. The surfactant is located near the surface of the substrate, on top of a layer of hydrophilic polyester. The consequences of the structure of the film-substrate interface on the adhesion properties is presented in Part III in this series.