Photonic Inks For Advanced Security Applications

• Autor(a) principal: Oliveira, Sofia Barroso Melo de
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/162285
• topic: Anti-counterfeiting; Photonic Inks; Color-shift; UV Scattering; TiO2 NPs; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

The global challenge of counterfeiting necessitates ongoing innovation in security measures. Optically variable inks (OVIs), known for their color variations under different lighting conditions, offer effective anti-counterfeit solutions. However, they primarily operate within the visible spectrum and are costly. This thesis aims to create cost-effective, scalable, and durable UV-sensitive OVIs with distinct optical variations, including notable extinction peaks in the ultraviolet (UV) spectrum. These specialized OVIs enhance security by remaining invisible to the naked eye but detectable with UV- sensitive devices. Achieving UV sensitivity involves utilizing dielectric nanoparticles (NPs) like titanium dioxide (TiO2), which allows peak resonant interactions with light in the desired spectral range and offers cost-effectiveness and environmental compatibility. This innovation enables photonic authentication based on light scattering, resulting in spectral and intensity changes for various viewing angles, enhancing security. Extensive experimental testing, guided by modeling results, led to the development of UV- sensitive photonic films incorporating TiO2 NPs on polycarbonate substrates. These films exhibit distinct optical resonance within the near-UV range. Key findings include the superior performance of ethanol-based formulations, in particular those with ethylene glycol, and polyvinyl pyrrolidone additives, as well as the identification of an optimal NP concentration, testing concentrations as low as 0.05% (m/V). Additionally, this research also revealed the significant enhancement of the extinction peaks achieved through the addition of fluorescent particles to the ink formulations, in some instances doubling the intensity of films without fluorescent particles. This work also identified the optimum inkjet and flexographic printing parameters, resulting in prints with highly prominent extinction peaks at 350 nm of up to 13%, accompanied by clearly observable angular color-shift effects. This research represents a significant step forward in the development of UV-sensitive OVIs with robust security features, contributing to advancements in anti-counterfeiting technologies across various industries.