Research Papers

Nanocrystalline cellulose for covert optical encryption

[+] Author Affiliations
Yu Ping Zhang

McGill University, Department of Electrical and Computer Engineering, Montreal, Quebec, Canada H3A 0G4

Vamsy P. Chodavarapu

McGill University, Department of Electrical and Computer Engineering, Montreal, Quebec, Canada H3A 0G4

Andrew G. Kirk

McGill University, Department of Electrical and Computer Engineering, Montreal, Quebec, Canada H3A 0G4

Mark P. Andrews

McGill University, Department of Chemistry, 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0G4

J. Nanophoton. 6(1), 063516 (Jul 02, 2012). doi:10.1117/1.JNP.6.063516
History: Received April 18, 2012; Revised May 28, 2012; Accepted May 30, 2012
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Abstract.  Nanocrystalline cellulose (NCC) solid films derived from spruce pulp exhibit iridescence when cast from chiral nematic aqueous phase suspensions of the nanocrystals. The iridescence has potential for overt encryption as an anti-counterfeiting measure and also offers an intrinsic level of covert encryption since 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 with ultraviolet (UV) light. The overall result is a selectively polarizing fluorescent iridescent film. We examined the impact of additions of OBA on NCC iridescence, optical activity, and physical structure variation with polarized optical microscopy, circular dichroism (CD) spectropolarimetry, and zeta potential analysis. Increasing OBA additions increase the chiral nematic pitch of NCC films and alter chiral nematic domain structure in the solid film. Under low-concentration conditions, OBA yields intense UV fluorescence without compromising the visible light iridescent properties of the film. The potential security offered by the NCC film can be authenticated using a UV light source, a circular polarizer in conjunction with an iridescent feature that can be verified by the eye or by chiral spectrometry.

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© 2012 Society of Photo-Optical Instrumentation Engineers

Citation

Yu Ping Zhang ; Vamsy P. Chodavarapu ; Andrew G. Kirk and Mark P. Andrews
"Nanocrystalline cellulose for covert optical encryption", J. Nanophoton. 6(1), 063516 (Jul 02, 2012). ; http://dx.doi.org/10.1117/1.JNP.6.063516


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