Iridescence

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Gruson Hugo - One of the best experts on this subject based on the ideXlab platform.

  • Quantitative characterization of iridescent colours in biological studies: a novel method using optical theory
    'The Royal Society', 2019
    Co-Authors: Gruson Hugo, Andraud Christine, Daney De Marcillac, Willy, Berthier Serge, Elias Marianne, Gomez Doris
    Abstract:

    International audienceIridescent colours are colours that change with viewing or illumination geometry. While they are widespread in many living organisms, most evolutionary studies on Iridescence do not take into account their full complexity. Few studies try to precisely characterize what makes iridescent colours special: their angular dependency. Yet, it is likely that this angular dependency has biological functions and is therefore submitted to evolutionary pressures. For this reason, evolutionary biologists need a repeatable method to measure iridescent colours as well as variables to precisely quantify the angular dependency. In this study, we use a theoretical approach to propose five variables that allow one to fully describe iridescent colours at every angle combination. Based on the results, we propose a new measurement protocol and statistical method to reliably characterize Iridescence while minimizing the required number of time-consuming measurements. We use hummingbird iridescent feathers and butterfly iridescent wings as test cases to demonstrate the strengths of this new method. We show that our method is precise enough to be potentially used at intraspecific level while being also time-efficient enough to encompass large taxonomic scales

  • Origin, functions and evolution of Iridescence in birds : the example of hummingbirds
    HAL CCSD, 2019
    Co-Authors: Gruson Hugo
    Abstract:

    The study of colour can offer valuable insights into the fine details of evolutive mechanisms. It is indeed a complex trait, which can evolve along several dimensions, and which is controlled by multiple selective pressures with often opposed effects. Yet, there is one class of colours that has received few attention from evolutionary biologists: iridescent colours. This is due to the inherent complexity of these colours and the fact that their sole quantitative measurement is a challenge in itself. During my PhD, I worked with physicists and biologists and I used optical theory to propose a new measurement method for iridescent colours. I then validated this method empirically by showing that it produced reliable and repeatable estimates for both hummingbirds and morpho butterflies. My work during these three years has also focused on the development of other methodological tools and software for the study of colours. I also focused more precisely on iridescent colours in hummingbirds. I mainly investigated two sides of this topic and tried to find out (i) the proximal causes of Iridescence in hummingbirds: how do they produce the striking colours they are renowned for? (ii) the distal causes of Iridescence: what are the evolutionary mechanisms which control the evolution of Iridescence at the community level. I found out that the structures producing Iridescence in hummingbirds are way more diverse than what we previously thought. They even display an usual type of structure which has not been described in any other group yet. I also showed that at the interspecific level, iridescent colours on the back of hummingbirds tend to be similar among species occupying the same communities, which suggests a possible role of the environment in the evolution of these colours, possibly for camouflage against predators.La couleur constitue un trait particulièrement intéressant pour étudier les mécanismes de l'évolution car il s'agit d'un trait complexe, qui peut évoluer dans plusieurs dimensions, et qui est soumis à des nombreuses pression évolutives, qui agissent généralement dans des directions opposées. Parmi les couleurs, il existe une classe qui a reçu relativement peu d'attention de la part des biologistes évolutifs jusqu'ici du fait de sa complexité et de la difficulté à la mesurer de manière fiable et comparable entre espèces : les couleurs iridescentes. Les couleurs iridescentes sont habituellement définies comme des couleurs qui changent selon l'angle d'observation ou d'illumination. Au cours de cette thèse, j'ai collaboré avec des biologistes et des physiciens et j'ai utilisé la théorie optique pour construire une nouvelle méthode de mesure pour ces couleurs, que j'ai ensuite testée sur les colibris et les morphos. J'ai également développé d'autres outils méthodologiques et des librairies logicielles pour l'étude des couleurs. Je me suis ensuite intéressé plus précisément aux couleurs iridescentes des colibris et à leur origine (i) proximale : par quels mécanismes les colibris produisent-ils leurs couleurs extraordinaires ? (ii) distale : quels sont les processus qui contrôlent l'évolution de ces couleurs à l'échelle de la communauté toute entière. J'ai découvert que les structures responsables de l'Iridescence chez les colibris présentent bien plus de diversité que ce qu'on pensait jusqu'ici et ils ont également un type de structure qui n'a pour l'instant été observé dans aucun autre groupe. J'ai aussi montré qu'à l'échelle interspécifique, les couleurs iridescentes présentes sur le dos sont similaires parmi les espèces qui habitent la même communauté, ce qui suggère une sélection par l'environnement, pour le camouflage par exemple

  • Origine, fonctions et évolution de l'Iridescence chez les oiseaux : exemple chez les colibris
    2019
    Co-Authors: Gruson Hugo
    Abstract:

    La couleur constitue un trait particulièrement intéressant pour étudier les mécanismes de l'évolution car il s'agit d'un trait complexe, qui peut évoluer dans plusieurs dimensions, et qui est soumis à des nombreuses pression évolutives, qui agissent généralement dans des directions opposées. Parmi les couleurs, il existe une classe qui a reçu relativement peu d'attention de la part des biologistes évolutifs jusqu'ici du fait de sa complexité et de la difficulté à la mesurer de manière fiable et comparable entre espèces : les couleurs iridescentes. Les couleurs iridescentes sont habituellement définies comme des couleurs qui changent selon l'angle d'observation ou d'illumination. Au cours de cette thèse, j'ai collaboré avec des biologistes et des physiciens et j'ai utilisé la théorie optique pour construire une nouvelle méthode de mesure pour ces couleurs, que j'ai ensuite testée sur les colibris et les morphos. J'ai également développé d'autres outils méthodologiques et des librairies logicielles pour l'étude des couleurs. Je me suis ensuite intéressé plus précisément aux couleurs iridescentes des colibris et à leur origine (i) proximale : par quels mécanismes les colibris produisent-ils leurs couleurs extraordinaires ? (ii) distale : quels sont les processus qui contrôlent l'évolution de ces couleurs à l'échelle de la communauté toute entière. J'ai découvert que les structures responsables de l'Iridescence chez les colibris présentent bien plus de diversité que ce qu'on pensait jusqu'ici et ils ont également un type de structure qui n'a pour l'instant été observé dans aucun autre groupe. J'ai aussi montré qu'à l'échelle interspécifique, les couleurs iridescentes présentes sur le dos sont similaires parmi les espèces qui habitent la même communauté, ce qui suggère une sélection par l'environnement, pour le camouflage par exemple.The study of colour can offer valuable insights into the fine details of evolutive mechanisms. It is indeed a complex trait, which can evolve along several dimensions, and which is controlled by multiple selective pressures with often opposed effects. Yet, there is one class of colours that has received few attention from evolutionary biologists: iridescent colours. This is due to the inherent complexity of these colours and the fact that their sole quantitative measurement is a challenge in itself. During my PhD, I worked with physicists and biologists and I used optical theory to propose a new measurement method for iridescent colours. I then validated this method empirically by showing that it produced reliable and repeatable estimates for both hummingbirds and morpho butterflies. My work during these three years has also focused on the development of other methodological tools and software for the study of colours. I also focused more precisely on iridescent colours in hummingbirds. I mainly investigated two sides of this topic and tried to find out (i) the proximal causes of Iridescence in hummingbirds: how do they produce the striking colours they are renowned for? (ii) the distal causes of Iridescence: what are the evolutionary mechanisms which control the evolution of Iridescence at the community level. I found out that the structures producing Iridescence in hummingbirds are way more diverse than what we previously thought. They even display an usual type of structure which has not been described in any other group yet. I also showed that at the interspecific level, iridescent colours on the back of hummingbirds tend to be similar among species occupying the same communities, which suggests a possible role of the environment in the evolution of these colours, possibly for camouflage against predators

  • Origine et fonctions des couleurs iridescentes chez les colibris
    HAL CCSD, 2019
    Co-Authors: Gruson Hugo
    Abstract:

    The study of colour can offer valuable insights into the fine details of evolutionary mechanisms. It is indeed a complex trait, which can evolve along several dimensions, and which is controlled by multiple selective pressures with often opposed effects. Yet, there is one class of colours that has received few attention from evolutionary biologists: iridescent colours. This is due to the inherent complexity of these colours and the fact that their sole quantitative measurement is a challenge in itself. During my PhD, I worked with physicists and biologists and I used optical theory to propose a new measurement method for iridescent colours. I then validated this method empirically by showing that it produced reliable and repeatable estimates for both hummingbirds and \textit{Morpho} butterflies. My work during these three years has also focused on the development of other methodological tools and software for the study of colours. I also focused more precisely on iridescent colours in hummingbirds. I mainly investigated two sides of this topic and tried to find out (i) the proximate causes of Iridescence in hummingbirds: how do they produce the striking colours they are renowned for? (ii) the ultimate causes of Iridescence: what are the evolutionary mechanisms which control the evolution of Iridescence at the community level? I found out that the structures producing Iridescence in hummingbirds are way more diverse than what we previously thought. They even display an usual type of structure which has not been described in any other group yet. I also showed that at the interspecific level, iridescent colours on the back of hummingbirds tend to be similar among species occupying the same communities, which suggests a possible role of the environment in the evolution of these colours, possibly for camouflage against predators. On the other hand, colours on the belly tend to be more similar than expected by change among co-occurring species, which suggests a role of selection for communication.La couleur constitue un trait particulièrement intéressant pour étudier les mécanismes de l'évolution car il s'agit d'un trait complexe, qui peut évoluer dans plusieurs dimensions, et qui est soumis à de nombreuses pressions évolutives, qui agissent généralement dans des directions opposées. Parmi les couleurs, il existe une classe qui a reçu relativement peu d'attention de la part des biologistes évolutifs jusqu'ici du fait de sa complexité et de la difficulté à la mesurer de manière fiable et comparable entre espèces : les couleurs iridescentes. Les couleurs iridescentes sont habituellement définies comme des couleurs qui changent selon l'angle d'observation ou d'illumination. Au cours de cette thèse, j'ai collaboré avec des biologistes et des physiciens et j'ai utilisé la théorie optique pour construire une nouvelle méthode de mesure pour ces couleurs, que j'ai ensuite testée sur les colibris et les papillons \textit{Morpho}. J'ai également développé d'autres outils méthodologiques et des librairies logicielles pour l'étude des couleurs. Je me suis ensuite intéressé plus précisément aux couleurs iridescentes des colibris et à leur origine (i) proximale : par quels mécanismes les colibris produisent-ils leurs couleurs extraordinaires ? (ii) ultime : quels sont les processus qui contrôlent l'évolution de ces couleurs à l'échelle de la communauté toute entière ? J'ai découvert que les structures responsables de l'Iridescence chez les colibris présentent bien plus de diversité que ce qu'on pensait jusqu'ici et ils ont également un type de structure qui n'a pour l'instant été observé dans aucun autre groupe. J'ai aussi montré qu'à l'échelle interspécifique, les couleurs iridescentes présentes sur le dos sont similaires parmi les espèces qui habitent la même communauté, ce qui suggère une sélection par l'environnement, pour le camouflage par exemple, alors que celles sur le ventres sont plus différentes qu'attendu au hasard, ce qui suggère une sélection pour la communication

Adam Aurèle - One of the best experts on this subject based on the ideXlab platform.

  • Photonics4All Bookmark Bubble (Italian)
    2018
    Co-Authors: Adam Aurèle
    Abstract:

    The purpose of the bookmarks for the project Photonics4All is to increase the public awareness of photonics and especially of the technological advances of photonics which have changed and improved everyday life (basic technology introduction). Why do soap bubbles have colour? Light reflects off both the inner and outer surfaces of a soap bubble. As the bubble dries out it changes thickness and the light waves reflecting off both surfaces have to travel different distances. White light is made up of all different colours – or waves of different lengths and - when light waves meet – or overlap - they create different colours.  Because reflected light travels different distances due to the different film thicknesses we see Iridescence in soap bubbles. This phenomenon is used in photonics to provide anti-reflection coating on your glasses for example.  

  • Photonics4All Bookmark Bubble (Dutch)
    2018
    Co-Authors: Adam Aurèle
    Abstract:

    The purpose of the bookmarks for the project Photonics4All is to increase the public awareness of photonics and especially of the technological advances of photonics which have changed and improved everyday life (basic technology introduction). Why do soap bubbles have colour? Light reflects off both the inner and outer surfaces of a soap bubble. As the bubble dries out it changes thickness and the light waves reflecting off both surfaces have to travel different distances. White light is made up of all different colours – or waves of different lengths and - when light waves meet – or overlap - they create different colours.  Because reflected light travels different distances due to the different film thicknesses we see Iridescence in soap bubbles. This phenomenon is used in photonics to provide anti-reflection coating on your glasses for example.  

  • Photonics4All Bookmark Bubble (German)
    2018
    Co-Authors: Adam Aurèle
    Abstract:

    The purpose of the bookmarks for the project Photonics4All is to increase the public awareness of photonics and especially of the technological advances of photonics which have changed and improved everyday life (basic technology introduction). Why do soap bubbles have colour? Light reflects off both the inner and outer surfaces of a soap bubble. As the bubble dries out it changes thickness and the light waves reflecting off both surfaces have to travel different distances. White light is made up of all different colours – or waves of different lengths and - when light waves meet – or overlap - they create different colours.  Because reflected light travels different distances due to the different film thicknesses we see Iridescence in soap bubbles. This phenomenon is used in photonics to provide anti-reflection coating on your glasses for example.  

  • Photonics4All Bookmark Bubble (Portuguese)
    2018
    Co-Authors: Adam Aurèle
    Abstract:

    The purpose of the bookmarks for the project Photonics4All is to increase the public awareness of photonics and especially of the technological advances of photonics which have changed and improved everyday life (basic technology introduction). Why do soap bubbles have colour? Light reflects off both the inner and outer surfaces of a soap bubble. As the bubble dries out it changes thickness and the light waves reflecting off both surfaces have to travel different distances. White light is made up of all different colours – or waves of different lengths and - when light waves meet – or overlap - they create different colours.  Because reflected light travels different distances due to the different film thicknesses we see Iridescence in soap bubbles. This phenomenon is used in photonics to provide anti-reflection coating on your glasses for example.  

  • Photonics4All Bookmark Bubble (Swedish)
    2018
    Co-Authors: Adam Aurèle
    Abstract:

    The purpose of the bookmarks for the project Photonics4All is to increase the public awareness of photonics and especially of the technological advances of photonics which have changed and improved everyday life (basic technology introduction). Why do soap bubbles have colour? Light reflects off both the inner and outer surfaces of a soap bubble. As the bubble dries out it changes thickness and the light waves reflecting off both surfaces have to travel different distances. White light is made up of all different colours – or waves of different lengths and - when light waves meet – or overlap - they create different colours.  Because reflected light travels different distances due to the different film thicknesses we see Iridescence in soap bubbles. This phenomenon is used in photonics to provide anti-reflection coating on your glasses for example.  

Freyre, Lauce Rubén - One of the best experts on this subject based on the ideXlab platform.

  • Posibles causas de una mortandad de pejerrey, Odontesthes bonariensis, en la laguna de Monte
    Instituto de Limnología "Raúl A. Ringuelet" Facultad de Ciencias Naturales y Museo (UNLP), 2019
    Co-Authors: Freyre, Lauce Rubén, Maroñas, Miriam E., Sendra, Eduardo Daniel, Cornejo Alejandra
    Abstract:

    Between the 18 and 20 of April of 1998 a silvers side fish kill was observed in Monte urban shallow lake. Rains preceded the phenomenon without being observed lake water level variations, but Iridescence in the surface was noticed. Sampled dead fish were obtained for measurement and autopsies were carried out as well. The size range was between 90 and 180 mm of standard length. The fish measurements were made in 21 specimens with best conservation condition and results concerning cephalic index and condition factor were compared with those obtained in previous years. Since most presented high degree of decomposition it was only possible to dissect the gills. Microscopic images of these didn’t record the presence infectious agents so it was discarded as a possible cause. The somatic relationships and indexes show that these fish have suffered growth difficulties which, coupled with the analysis of the gills, supports the hypothesis of an environmental alteration as responsible for the fish kill. Variation leading to an increment in the concentration of organic matter (MO) in the lake produced by the rain induced transport of MO accumulated in the basin of the tributary (channeled), possibly further potentates by the incorporation of hydrocarbons, given the observed Iridescence. But this cannot be confirmed by lack of water sample. The made interpretations don’t allow to deduce the cause of the fish kill but enable to point out that the environmental phenomenon that provoked it possibly had not lead to the recorded consequences if the population had been less susceptible, more like under the conditions of previous years.Between the 18 and 20 of April of 1998 a silvers side fish kill was observed in Monte urban shallow lake. Rains preceded the phenomenon without being observed lake water level variations, but Iridescence in the surface was noticed. Sampled dead fish were obtained for measurement and autopsies were carried out as well. The size range was between 90 and 180 mm of standard length. The fish measurements were made in 21 specimens with best conservation condition and results concerning cephalic index and condition factor were compared with those obtained in previous years. Since most presented high degree of decomposition it was only possible to dissect the gills. Microscopic images of these didn’t record the presence infectious agents so it was discarded as a possible cause. The somatic relationships and indexes show that these fish have suffered growth difficulties which, coupled with the analysis of the gills, supports the hypothesis of an environmental alteration as responsible for the fish kill. Variation leading to an increment in the concentration of organic matter (MO) in the lake produced by the rain induced transport of MO accumulated in the basin of the tributary (channeled), possibly further potentates by the incorporation of hydrocarbons, given the observed Iridescence. But this cannot be confirmed by lack of water sample. The made interpretations don’t allow to deduce the cause of the fish kill but enable to point out that the environmental phenomenon that provoked it possibly had not lead to the recorded consequences if the population had been less susceptible, more like under the conditions of previous years

  • Posibles causas de una mortandad de pejerrey, Odontesthes bonariensis, en la laguna de Monte
    2018
    Co-Authors: Freyre, Lauce Rubén, Maroñas, Miriam E., Sendra, Eduardo Daniel, Cornejo A.
    Abstract:

    Between the 18 and 20 of April of 1998 a silvers side fish kill was observed in Monte urban shallow lake. Rains preceded the phenomenon without being observed lake water level variations, but Iridescence in the surface was noticed. Sampled dead fish were obtained for measurement and autopsies were carried out as well. The size range was between 90 and 180 mm of standard length. The fish measurements were made in 21 specimens with best conservation condition and results concerning cephalic index and condition factor were compared with those obtained in previous years. Since most presented high degree of decomposition it was only possible to dissect the gills. Microscopic images of these didn’t record the presence infectious agents so it was discarded as a possible cause. The somatic relationships and indexes show that these fish have suffered growth difficulties which, coupled with the analysis of the gills, supports the hypothesis of an environmental alteration as responsible for the fish kill. Variation leading to an increment in the concentration of organic matter (MO) in the lake produced by the rain induced transport of MO accumulated in the basin of the tributary (channeled), possibly further potentates by the incorporation of hydrocarbons, given the observed Iridescence. But this cannot be confirmed by lack of water sample. The made interpretations don’t allow to deduce the cause of the fish kill but enable to point out that the environmental phenomenon that provoked it possibly had not lead to the recorded consequences if the population had been less susceptible, more like under the conditions of previous years.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

Ullrich Steiner - One of the best experts on this subject based on the ideXlab platform.

  • the flower of hibiscus trionum is both visibly and measurably iridescent
    New Phytologist, 2015
    Co-Authors: Silvia Vignolini, Ullrich Steiner, Edwige Moyroud, T Hingant, Hannah Banks, Paula J Rudall, Beverley J Glover
    Abstract:

    Summary ! Living organisms can use minute structures to manipulate the reflection of light and display colours based on interference. There has been debate in recent literature over whether the diffractive optical effects produced by epoxy replicas of petals with folded cuticles persist and induce Iridescence in the original flowers when the effects of petal pigment and illumination are taken into account. ! We explored the optical properties of the petal of Hibiscus trionum by macro-imaging, scanning and transmission electron microscopy, and visible and ultraviolet (UV) angle-resolved spectroscopy of the petal. ! The flower of Hibiscus trionum is visibly iridescent, and the Iridescence can be captured photographically. The Iridescence derives from a diffraction grating generated by folds of the cuticle. The Iridescence of the petal can be quantitatively characterized by spectrometric measurements with several square-millimetres of sample area illuminated. ! The flower of Hibiscus trionum has the potential to interact with its pollinators (honeybees, other bees, butterflies and flies) through iridescent signals produced by its cuticular diffraction grating.

  • Biomimetic layer-by-layer assembly of artificial nacre
    Nature Communications, 2012
    Co-Authors: Ullrich Steiner
    Abstract:

    Nacre is a technologically remarkable organic-inorganic composite biomaterial. It consists of an ordered multilayer structure of crystalline calcium carbonate platelets separated by porous organic layers. This microstructure exhibits both optical Iridescence and mechanical toughness, which transcend those of its constituent components. Replication of nacre is essential for understanding this complex biomineral, and paves the way for tough coatings fabricated from cheap abundant materials. Fabricating a calcitic nacre imitation with biologically similar optical and mechanical properties will likely require following all steps taken in biogenic nacre synthesis. Here we present a route to artificial nacre that mimics the natural layer-by-layer approach to fabricate a hierarchical crystalline multilayer material. Its structure-function relationship was confirmed by nacre-like mechanical properties and striking optical Iridescence. Our biomimetic route uses the interplay of polymer-mediated mineral growth, combined with layer-by-layer deposition of porous organic films. This is the first successful attempt to replicate nacre, using CaCO3.

  • response to comment on floral Iridescence produced by diffractive optics acts as a cue for animal pollinators
    Science, 2009
    Co-Authors: Heather M Whitney, Ullrich Steiner, Mathias Kolle, Piers Andrew, Lars Chittka, Beverley J Glover
    Abstract:

    Morehouse and Rutowski make interesting comments on the difficulties of untangling complex optical phenomena. However, our use of a four-colored transfer test in our original study, along with spectrophotometric analysis of the nonoverlapping colors produced by our target disks, allows us to conclude that bees can learn to use Iridescence as a foraging cue.

  • floral Iridescence produced by diffractive optics acts as a cue for animal pollinators
    Science, 2009
    Co-Authors: Heather M Whitney, Ullrich Steiner, Mathias Kolle, Piers Andrew, Lars Chittka, Beverley J Glover
    Abstract:

    Iridescence, the change in hue of a surface with varying observation angles, is used by insects, birds, fish, and reptiles for species recognition and mate selection. We identified Iridescence in flowers of Hibiscus trionum and Tulipa species and demonstrated that Iridescence is generated through diffraction gratings that might be widespread among flowering plants. Although Iridescence might be expected to increase attractiveness, it might also compromise target identification because the object9s appearance will vary depending on the viewer9s perspective. We found that bumblebees (Bombus terrestris) learn to disentangle flower Iridescence from color and correctly identify iridescent flowers despite their continuously changing appearance. This ability is retained in the absence of cues from polarized light or ultraviolet reflectance associated with diffraction gratings.

Mark P Andrews - One of the best experts on this subject based on the ideXlab platform.

  • structured color humidity indicator from reversible pitch tuning in self assembled nanocrystalline cellulose films
    Sensors and Actuators B-chemical, 2013
    Co-Authors: Yu Ping Zhang, Andrew G Kirk, Vamsy P. Chodavarapu, Mark P Andrews
    Abstract:

    Abstract Iridescence is an example of structured color that is widespread in the biosphere, exhibited by multilayer inorganic thin films for optical filters, photonic crystals and other materials in which the periodic patterning of matter interacts with an electromagnetic field. Nanocrystalline cellulose (NCC) can be cast in the form of thick iridescent films whose color originates in the multi-domain chiral nematic texture created by self-assembly of the rigid rod crystallites. Scanning electron microscopy confirms the periodic layer structure that arises from the helical twist axis of the chiral nematic mesophase film. In effect, the film comprises multi-domain Bragg reflectors. On exposure to liquid water, and high relative humidity (RH), a reversible shift in the film Iridescence from dry state blue-green to wet state red-orange is observed. This color change, which requires no pigment, is quantified by reflectance spectroscopy. The color transition is attributed to sorption of water that causes the pitch of the Bragg reflector to enlarge, and this leads to a red shift in the Iridescence. The subsequent expansion of the film thickness was observed using polarized optical microscopy. The effect resembles molecular dopant and electric field induced pitch tuning along the helicoid axis in one-dimensional photonic crystal-like chiral nematic molecular systems. The color shift for a 40 μm thick NCC film is slow, occurring on timescale of 1–3 min. Thinner films change color in less than 2 s.

  • Nanocrystalline cellulose for covert optical encryption
    Journal of Nanophotonics, 2012
    Co-Authors: Yu Ping Zhang, Andrew G Kirk, Vamsy P. Chodavarapu, Mark P Andrews
    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.

  • Nanocrystalline cellulose for covert optical encryption
    Proceedings of SPIE, 2012
    Co-Authors: Yu Ping Zhang, Andrew G Kirk, Vamsy P. Chodavarapu, Mark P Andrews
    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.

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