Nature's most vivid colours rely on ordered structures with lattice constants on the order of the wavelength of visible radiation. Knowledge of the interplay between the morphology, composition and optical appearance of biological photonic systems can provide inspiration for novel artificial photonic materials [M. Kolle, et al. Nat. Nanotech. 5, 511 (2010)]. Plants develop nanostructured tissues with a strong photonic response. Many flowers develop a striated epidermal layer that produces iridescent colouration [H. M. Whitney et al. Science 325, 449 (2009)]. In the case of the Pollia fruits, a chiral multilayered structures is observed, see Fig.1.  Cellulose micro-fibrils form a chiral multilayer structure, called a helicoid [S.Vignolini et al. PNAS (2012)]. In each component layer, cellulose micro-fibrils lie parallel to one another, with successive layers offset from each other at a small angle, so that the direction of the parallel-aligned micro-fibrils changes consistently, rotating from one layer to another. When the distance between consecutive layers in which the cellulose micro-fibrils have the same direction is comparable with the wavelength of light, a strong and colour-selective reflection of circularly polarized light in a narrow wavelength region is found. Coloration produced by nanostructures depends only on the distance between layers after a complete rotation of the micro-fibril orientation. By changing this distance it is possible to vary the colour of the structure through the entire visible range. In this talk different ways to produce photonc structures with cellulose will be reviewed.  Biomimetics with cellulose-based architectures is key to understand biological processes at work during the growth of these structures in plants cell wall.  Moreover it enables us to fabricate novel photonic structures using low cost materials in ambient conditions, since cellulose is the most abundant polymer available.(a) Picture of Pollia fruit, and (b) nano-structure cell wall resposable for the fruit colouration.

Cellulose based biomimetic photonic structures

247th National Meeting (2014)

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