Mimicking the Structural Color of Insects

Nanostructures of a cellulose derivative to mimic structural colors of insects. (Source: ICMAB)

The bright colors of some butter­flies, beetles or birds are not due to the presence of pigments that selec­tively absorb light, but due to the structural colora­tion. Structural colora­tion occurs on surfaces with a nano­structure with dimen­sions similar to those of the wave­length of the incident light. These ordered nano­structures are known as photonic crystals. There is a great interest in providing cellu­lose, the most abundant polymer in earth, biocom­patible and bio­gradable, with these structures, which can offer new optical and electric func­tionalities.

Now, Agustín Mihi and colleagues of the Institute of Materials Science of Barce­lona ICMAB-CSIC create for the first time photonic crystals and plasmonic structures of a cellu­lose derivative through its nano­structuring with the soft lithography technique. By perio­dically nano­structuring the cellulose film, it is no longer trans­parent and begins to reflect intense colors, depending on the pattern with which it has been molded. With this new, fully scalable and low cost technique, alternative to the tradi­tional self-assembly of cellulose nano­crystals, a high quality and repro­ducible nano­structure is created on this polymer in a very short time, and achieving a wide range of iri­descent colors, only depending on the size and morpho­logy of the created structures.

These photonic crystals can be nano­imprinted on different substrates to provide photonic proper­ties on surfaces that do not present this property, such as paper, demonstra­ting the potential of this tech­nology as photonic ink, for appli­cations in anti-counter­feiting tech­nology, packaging, deco­rative paper, labels or sensors, among others. When these structures are covered with a thin metal layer, they acquire plasmonic proper­ties while main­taining their flexi­bility, achieving brighter colors. Further­more, depending on the type of cellulose deri­vative used, its degree of biode­grada­bility and solubility in water can be tuned. These plasmonic structures can be used as dis­posable sensors for Raman emission or to increase the light emitted by a dye. (Source: ICMAB)

Reference: A. Espinha et al.: Hydroxypropyl cellulose photonic architectures by soft nanoimprinting lithography, Nat. Phot., online 9 April 2018; DOI: 10.1038/s41566-018-0152-1

Link: Optoelectronics of nanostructures, Institute of Materials Science of Barcelona ICMAB-CSIC, Barcelona, Spain

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