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Proceedings Paper

Nanocrystalline cellulose for covert optical encryption
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Paper Abstract

Nanocrystalline cellulose solid films derived from spruce pulp exhibit iridescence when cast from chiral nematic aqueous phase suspensions of the nanocrystals. Iridescence is a color travel phenomenon that might have potential for overt encryption as an anti-counterfeiting measure. The iridescent phase also offers an intrinsic level of covert encryption by virtue of the fact that films of NCC reflect left-circularly polarized light. Addition of TINOPAL, an optical brightening agent (OBA), adds a third level of (covert) encryption potential since the chromophore exhibits strong fluorescence when excited at ultra-violet wavelengths. The overall result is a selectively polarizing fluorescent iridescent film. We study the impact of additions of OBA on NCC iridescence, optical activity, and physical structure variation with polarized optical microscopy, circular dichroism spectropolarimetry and zeta potential analysis. Increasing OBA additions increase the chiral nematic pitch of NCC films, and this in turn alters chiral nematic domain structure in the solid film. Under low concentration conditions defined by our experiments, OBA yields intense UV fluorescence, without compromising the visible light iridescent properties of the film. The potential security offered by NCC and its optical responses can be authenticated using a UV light source such as is commonly used for banknote verification, a circular polarizer in conjunction with an iridescent feature which can be verified by the eye or by chiral spectrometry.

Paper Details

Date Published: 17 February 2012
PDF: 9 pages
Proc. SPIE 8258, Organic Photonic Materials and Devices XIV, 825808 (17 February 2012); doi: 10.1117/12.906770
Show Author Affiliations
Yu Ping Zhang, McGill Univ. (Canada)
Vamsy P. Chodavarapu, McGill Univ. (Canada)
Andrew G. Kirk, McGill Univ. (Canada)
Mark P. Andrews, McGill Univ. (Canada)

Published in SPIE Proceedings Vol. 8258:
Organic Photonic Materials and Devices XIV
Christopher Tabor; François Kajzar; Toshikuni Kaino; Yasuhiro Koike, Editor(s)

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