In our latest article, we explore the existence of a diffusion phenomenon at the interface of laser welded polymer-metal assemblies. The results show that a diffusion of the metal in the polymer actually occurs at a very small scale - about 20 nm - compared to the scale of the welding. Nonetheless, it sheds a new light on our understanding of the laser welding process, hence of the adhesion process in this case. This article was published in open access.
To assess the diffusion phenomenon, mirror polished aluminum was spin-coated with polyamide-6.6 and then laser welded. Two depth profiles were acquired in ToF-SIMS in and out of the weld. In the article, we discuss the use of a new methodology to locate the interface of the two materials, using information entropy. It was already proposed [1] and used to help the analysis of ToF-SIMS depth profiles, but in our simple case (only one interface of two very different materials), we go one step further. This methodology offers a better way to locate interfaces by removing a possible user bias. The intensity of aluminum ions was then modelized using Fick's second law describing diffusion, but also fitting the intensity behavior at the interface in ToF-SIMS depth profiles. The values in and out of the weld were compared and a discrepancy of about 20 nm was underlined, proving the existence of a diffusion phenomenon.
[1] S. Aoyagi, K. Mizomichi, K. Kamochi, A. Miisho, Interpretation of TOF-SIMS data based on information entropy of spectra, Surface and Interface Analysis 54 (2021) 356–362. https://doi.org/10.1002/sia.7047.
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