Nanocrystalline cellulose (NCC) exhibits unusual optical properties that make it of interest for hierarchical optical encryption in nanostructured films. The color-travel phenomenon of iridescence is exhibited by NCC when cast as a film from chiral nematic aqueous phase suspensions of the nanocrystals. “Iridescence by self-assembly” has potential for overt encryption as an anti-counterfeiting measure. It also offers an intrinsic level of covert encryption by reflecting leftcircularly polarized light. We show that addition of a UV sensitive dye adds another level of (covert) encryption, and that specially prepared films manifest a rare form of optical non-reciprocity that does not require the application of an external field. Chirality parameters and stokes vector analyses suggest a simple authentication scheme. The method uses a UV light source and a circular polarizer in conjunction with an iridescent feature that can be verified by the eye or by chiral spectrometry.

Date Published: 27 August 2014
PDF: 13 pages
Proc. SPIE 9172, Nanostructured Thin Films VII, 91720R (27 August 2014); doi: 10.1117/12.2062974

Published in SPIE Proceedings Vol. 9172:
Nanostructured Thin Films VII
Akhlesh Lakhtakia; Tom G. Mackay; Motofumi Suzuki, Editor(s)