Browsing by Author "Stepanenko, Dimitrije"

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    Naturally safe: Cellular noise for document security
    Pavlović, Danica; Rabasović, Mihailo; Krmpot, Aleksandar; Lazović, Vladimir; Čurčić, Srećko; Stojanović, Dejan; Jelenković, Branislav; Zhang, Wang; Zhang, Di; Vukmirović, Nenad; Stepanenko, Dimitrije; Kolarić, Branko; Pantelić, Dejan
    Modern document protection relies on the simultaneous combination of many optical features with micron and submicron structures, whose complexity is the main obstacle for unauthorized copying. In that sense, documents are best protected by the diffractive optical elements generated lithographically and mass‐produced by embossing. The problem is that the resulting security elements are identical, facilitating mass‐production of both original and counterfeited documents. Here, we prove that each butterfly wing‐scale is structurally and optically unique and can be used as an inimitable optical memory tag and applied for document security. Wing‐scales, exhibiting angular variability of their color, were laser‐cut and bleached to imprint cryptographic information of an authorized issuer. The resulting optical memory tag is extremely durable, as verified by several century‐old insect specimens still retaining their coloration. The described technique is simple, amenable to mass‐production, low cost and easy to integrate within the existing security infrastructure.
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    Nitrogen plasma surface treatment for improving polar ink adhesion on micro/nanofibrillated cellulose films
    Dimić-Mišić, Katarina; Kostić, Mirjana; Obradović, Bratislav; Kramar, Ana; Jovanović, Stevan; Stepanenko, Dimitrije; Mitrović-Dankulov, Marija; Lazović, Saša; Johansson, Leena-Sisko; Maloney, Thad; Gane, Patrick
    We find that nitrogen plasma treatment of micro/nanofibrillated cellulose films increases wettability of the surface by both liquid polar water and nonpolar hexadecane. The increased wetting effect is more pronounced in the case of polar liquid, favouring the use of plasma treated micro/nanofibrillated cellulose films as substrates for a range of inkjet printing including organic-based polar-solvent inks. The films were formed from aqueous suspensions of progressively enzymatic pretreated wood-free cellulose fibres, resulting in increased removal of amorphous species producing novel nanocellulose surfaces displaying increasing crystallinity. The mechanical properties of each film are shown to be highly dependent on the enzymatic pretreatment time. The change in surface chemistry arising from exposure to nitrogen plasma is revealed using X-ray photoelectron spectroscopy. That both polar and dispersive surface energy components become increased, as measured by contact angle, is also linked to an increase in surface roughness. The change in surface free energy is exemplified to favour the trapping of photovoltaic inks.