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  4. A code with a twist: Supraparticle microrod composites with direction dependent optical properties as anti-counterfeit labels
 
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2019
Journal Article
Titel

A code with a twist: Supraparticle microrod composites with direction dependent optical properties as anti-counterfeit labels

Abstract
Superparamagnetic iron oxide nanoparticles can be assembled to form anisotropic microrod supraparticles with the assistance of a magnetic field during synthesis. Optionally, these iron oxide microrods can furthermore be coated with a thin silica shell. Due to their anisotropic structure, both microrod types can be aligned in a magnetic field while being dispersed in a matrix material which can be cured during the alignment of the microrods. In this way, an anisotropic magnetic composite is obtained. Interestingly, it was observed that the optical extinction properties for visible light in such a composite are direction dependent, which can be explained by using appropriate models based on Maxwell equations. Based on the understanding of this principle, a clever approach for a hidden code could be proposed which is obtained from mixing pure iron oxide and silica coated microrod supraparticles in such an anisotropic composite. The hidden code, which comes down to obtaining a single value eventually, can only be revealed when knowing that the system needs to be measured with a certain "twist".
Author(s)
Wintzheimer, Susanne
Fraunhofer-Institut für Silicatforschung ISC
Granath, Tim
Fraunhofer-Institut für Silicatforschung ISC
Eppinger, Antonia
Fraunhofer-Institut für Silicatforschung ISC
Gonçalves, Manuel Rodrigues
Mandel, Karl
Fraunhofer-Institut für Silicatforschung ISC
Zeitschrift
Nanoscale advances
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DOI
10.1039/C8NA00334C
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Fraunhofer-Institut für Silicatforschung ISC
Tags
  • nanoparticle

  • supraparticle

  • anisotropic composite

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