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- ItemStraightforward Approach for Preparing Durable Antibacterial ZnO Nanoparticle Coatings on Flexible Substrates(Basel : MDPI, 2022) Šutka, Andris; Mežule, Linda; Denisova, Viktorija; Meier-Haack, Jochen; Kulkarni, Akshay; Bitina, Sanda; Smits, Krisjanis; Vihodceva, SvetlanaFlexible antibacterial materials have gained utmost importance in protection from the distribution of bacteria and viruses due to the exceptional variety of applications. Herein, we demonstrate a readily scalable and rapid single-step approach for producing durable ZnO nanoparticle antibacterial coating on flexible polymer substrates at room temperature. Substrates used are polystyrene, poly(ethylene-co-vinyl acetate) copolymer, poly(methyl methacrylate), polypropylene, high density polyethylene and a commercial acrylate type adhesive tape. The deposition was achieved by a spin-coating process using a slurry of ZnO nanoparticles in toluene. A stable modification layer was obtained when toluene was a solvent for the polymer substrates, namely polystyrene and poly(ethylene-co-vinyl acetate). These coatings show high antibacterial efficiency causing >5 log decrease in the viable counts of Gram-negative bacteria Escherichia. coli and Gram-positive bacteria Staphylococcus aureus in 120 min. Even after tapping these coated surfaces 500 times, the antibacterial properties remained unchanged, showing that the coating obtained by the presented method is very robust. In contrast to the above findings, the coatings are unstable when toluene is not a solvent for the substrate.
- ItemNanostructuring of Fused Silica Assisted by Laser-shaped Metal Triangles Using a Nanosecond Laser(Amsterdam [u.a.] : Elsevier, 2016) Lorenz, Pierre; Grüner, Christoph; Ehrhardt, Martin; Bayer, Lukas; Zimmer, KlausSelf-organized processes are of special interest for the laser-induced nanostructuring of surfaces. In this study we combined two self-organized processes: the microsphere lithography and the molten phase transformation for the nanostructuring of dielectrics. A fused silica substrate was covered with periodically ordered polystyrene (PS) spheres and the system was subsequently covered with 30 nm chromium. Afterwards the PS spheres were removed and the bare and resultant periodic Cr triangles were irradiated in two steps using a KrF excimer laser. First step: A low laser fluence treatment results in a melting and shape transformation of the triangles. Second step: A high laser fluence treatment of the pre-treated surface results in a nanostructuring of the dielectric surface (and removal of the metal). The surface topography was studied by scanning electron microscopy. Furthermore, the different steps were simulated and compared with the experimental results.
- ItemShock-wave-induced Thin-film Delamination (SWIFD): A Non-thermal Structuring Method of Functional Layers(Amsterdam [u.a.] : Elsevier, 2016) Lorenz, Pierre; Ehrhardt, Martin; Bayer, Lukas; Zimmer, KlausThe laser structuring of thermally sensitive functional layers is a challenge for laser methods. However, already ultrashort laser pulses can induce thermal modifications. The spatial separation of the laser pulse absorption from the functional layer removal process allows a non-thermal structuring process. Therefore, the rear side of the substrate is irradiated and the following laser ablation process induces a transverse shock wave through the substrate. Finally, the interaction of the shock wave with the substrate/functional layer interface results in a delamination of the functional layer. This shock-wave-induced thin-film delamination (SWIFD) method was tested on a layer system (1.5 μm thick epoxy-based negative photoresist SU 8, 250 nm–1 μm chromium layer) on a 25 μm polyimide flexible substrate where the influence of the systematic variation of the thickness of the metallic intermediate layer on the delamination process was studied. The resultant surface morphology was analyzed by optical microscopy as well as by white light interferometry (WLI).