Nanocrystalline cellulose for optical encryption

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.

[1]  Mark P. Andrews,et al.  Structured color humidity indicator from reversible pitch tuning in self-assembled nanocrystalline cellulose films , 2013 .

[2]  M. Mccully,et al.  The use of an optical brightener in the study of plant structure. , 1975, Stain technology.

[3]  F. Livolant,et al.  Freeze-Fractures in Cholesteric Mesophases of Polymers , 1989 .

[4]  Jean-Marie Becker,et al.  Self-encryption for paper document authentication , 2007 .

[5]  Ashot Gevorgyan,et al.  Observation of optical non-reciprocity in a single layer of transparent linear chiral media with asymmetric boundaries , 2013 .

[6]  Mohan Srinivasarao,et al.  Structural Origin of Circularly Polarized Iridescence in Jeweled Beetles , 2009, Science.

[7]  I.B. Djordjevic,et al.  Novel super structured Bragg gratings for optical encryption , 2006, Journal of Lightwave Technology.

[8]  Jean-Pol Vigneron,et al.  Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera) , 2009, Journal of The Royal Society Interface.

[9]  A. C. Neville.  Molecular and mechanical aspects of helicoid development in plant cell walls , 1985 .

[10]  M. Roman,et al.  Parabolic focal conics in self-assembled solid films of cellulose nanocrystals. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[11]  Lu,et al.  Bragg reflection from cholesteric liquid crystals. , 1995, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[12]  Jean-Pol Vigneron,et al.  Structurally tuned iridescent surfaces inspired by nature , 2008 .

[13]  Hl. de Vries.  Rotatory power and other optical properties of certain liquid crystals , 1951 .

[14]  J. Vigneron,et al.  Color-selecting reflectors inspired from biological periodic multilayer structures. , 2006, Optics express.

[15]  Mark P. Andrews,et al.  Nanocrystalline cellulose for covert optical encryption , 2012 .

[16]  Wadood Y. Hamad,et al.  Parameters Affecting the Chiral Nematic Phase of Nanocrystalline Cellulose Films , 2010 .

[17]  Shuichi Kinoshita,et al.  Structural colors in nature: the role of regularity and irregularity in the structure. , 2005, Chemphyschem : a European journal of chemical physics and physical chemistry.

[18]  Andrew R. Parker,et al.  515 million years of structural colour , 2000 .

[19]  D. Gray,et al.  Chiral nematic ordering of polysaccharides , 1994 .

[20]  P. Hughes,et al.  Insect cuticular growth layers seen under the scanning electron microscope: A new display method. , 1987, Tissue & cell.

[21]  Mark P. Andrews,et al.  Origin of iridescence in chiral nematic phase nanocrystalline cellulose for encryption and enhanced color , 2011, OPTO.

[22]  D G Gray,et al.  Helicoidal self-ordering of cellulose microfibrils in aqueous suspension. , 1992, International journal of biological macromolecules.

[23]  Dirk J. Broer,et al.  Creation of Supramolecular Thin Film Architectures with Liquid-Crystalline Networks , 1995 .

[24]  R. Marchessault,et al.  In vitro chiral nematic ordering of chitin crystallites. , 1993, International journal of biological macromolecules.

[25]  D. Gubb,et al.  A direct visualisation of helicoidal architecture in Carcinus maenas and Halocynthia papillosa by scanning electron microscopy. , 1975, Tissue & cell.

[26]  M. Giraud‐Guille,et al.  Direct visualization of microtomy artefacts in sections of twisted fibrous extracellular matrices. , 1986, Tissue & cell.

[27]  M. Giraud‐Guille,et al.  Structure and Chirality of the Nematic Phase in α-Chitin Suspensions , 2004 .