Laser Welding of Transparent High Performance Polymer Foils by using Silver Nanoparticles as Absorption Layer
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Laser Welding of Transparent High Performance Polymer Foils by using Silver Nanoparticles as Absorption Layer Matthias Neuber and Andreas Heilmann Fraunhofer Institute for Mechanics of Materials IWM, Walter-Hülse-Straße 1, 06120 Halle (Saale), Germany ABSTRACT Laser welding of transparent high performance polymer foils requires an additional absorption layer at the interface of both foils. This paper demonstrates that metallic nanoparticles, e.g. gold, silver or copper, can act as such an absorption layer. Silver nanoparticles were deposited on the surface of 200 μm thick ethylene tetrafluoroethylene (ETFE) polymer foils by evaporation processes or by magnetron sputtering. For their additional mechanical stabilization, thin films produced by plasma polymerisation of hexamethyldisilazane or PTFEpolymer sputtering were deposited on top of the metal nanoparticles. Laser irradiation of the coated foil together with the untreated joining partner was performed by a continuous wave diode laser at a wavelength of 808 nm. With the defocused laser, the foils were welded and finally a nearly transparent welding seam was achieved. The nanostructure and the optical properties of the nanoparticle layer before laser irradiation were determined and compared with the nanostructure and the optical properties of the polymer metal nanocomposite after laser welding. INTRODUCTION Laser welding of polymers is a well-established process in polymer assembly and construction. The laser welding of two transparent polymers requires an additional absorption layer between the joining polymers parts. For these layers, special dye molecules which were developed only for these applications can be used [1]. The application of the dye molecule dispersions with polymeric components can be realized by various wet coating technologies, e.g. spraying or brushing with controlled drying. But, laser welding requires strong reproducibility and homogenous absorption of the coating which is hard to achieve. Further, the incorporation of the dye molecules and the surrounding polymeric coating into the welding seam can result in reduced long-time stability of the welding seam. Therefore, metallic nanoparticles were used as absorber for laser welding of polymer foils. Noble metal nanoparticles with a suitable particle size and shape can be easily deposited by different vacuum deposition techniques seem to be a promising alternative absorber layer. The optical properties of noble metallic nanoparticles embedded in polymer matrices are determined by their size and shape distribution, the spatial arrangement as well as on the surrounding media [2, 3]. The optical properties of these nanocomposite materials are a mixture of the properties of the basis components. If the metallic particles are embedded in an optical transparent media the optical properties are mainly dominated by these nanoparticles [4], [5], [6].
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The noble metals gold, silver and copper are metals demonstrating plasma resonances absorption in the visible spectral range. In the following, we des
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