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Issue 30, 2017
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Robust photonic microparticles comprising cholesteric liquid crystals for anti-forgery materials

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Abstract

Cholesteric liquid crystals (CLCs) possess a photonic bandgap owing to the helical arrangement of molecules. The CLCs reflect circularly-polarized light of a specific handedness and wavelength, exhibiting colors. The wavelength of the selective reflection, or the structural color, can be easily controlled by varying the concentration of a chiral dopant. Although this unique optical property renders CLCs promising for various applications, their fluidity severely limits the ease of processing and their structural stability. To overcome this limitation, we designed CLC microparticles (CLC-MPs) via photopolymerization of reactive mesogens (RMs) in CLC droplets. Using capillary microfluidic devices, highly uniform emulsion drops of CLC-RM mixtures were prepared in aqueous phase drops, which were then exposed to ultraviolet (UV) irradiation to obtain solid microparticles. The diameter of the CLC-MPs can be precisely controlled by either manipulating the flow rates of the dispersed and continuous phases or varying the diameter of the capillary orifice in the microfluidic devices. The wavelength of reflection and the handedness of the helical structure are selected via the composition of the dispersed phase. The photo-polymerization of RMs leads to the formation of a three-dimensional rigid network, thereby yielding CLC-MPs with high mechanical stability. The CLC-MPs could be further assembled to form two-dimensional hexagonal arrays on flat surfaces or deposited in pre-defined trenches or holes via mechanical rubbing. Moreover, two distinct CLC-MPs with opposite handedness can be patterned to show different color graphics depending on the selection of handedness of circularly-polarized light, which are appealing for anti-forgery patches.

Graphical abstract: Robust photonic microparticles comprising cholesteric liquid crystals for anti-forgery materials

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Publication details

The article was received on 15 Jun 2017, accepted on 01 Jul 2017 and first published on 04 Jul 2017


Article type: Paper
DOI: 10.1039/C7TC02660A
Citation: J. Mater. Chem. C, 2017,5, 7567-7573
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    Robust photonic microparticles comprising cholesteric liquid crystals for anti-forgery materials

    H. J. Seo, S. S. Lee, J. Noh, J. Ka, J. C. Won, C. Park, S. Kim and Y. H. Kim, J. Mater. Chem. C, 2017, 5, 7567
    DOI: 10.1039/C7TC02660A

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