03 - Tailoring disorder in functional optical materials using a combined materials engineering and bioinspiration approach

Natural systems are able to generate structural materials with unique functional properties. The formation of complex three-dimensional structures in nature is of fundamental importance to break the limits imposed by available construction elements, which are generally composed of organic compounds, i.e. biopolymers (polysaccharides and proteins). Structuring into ordered, and especially into irregular or disordered systems is the key to define new roadmaps to innovative engineering materials. Basic consideration on the importance of disordered structures in biology can be most efficiently demonstrated on natural optical materials. In our proposal we aim to identify biological optical structures which will allow a distinct photon management for broad band interaction in addition to specific wavelength selectivity for angle-independent reflection. In nature, such systems are realised in the complex structure of some butterfly species.

We will first work on the so-called pepper-pot structure with a distinct degree of disorder, frequently found in butterflies. The pepper-pot structure will be subjected to numerical calculations in order to find an optimised structure fulfilling the above envisioned optical characteristics, which will require the formation of tailor-made degree of disorder in the structures. These identified structures are then abstracted (bioinspired engineering) and the resulting architectures will be fabricated via direct laser writing (DLW) using conventional acrylates. Since DLW has a lower limit of approximately one micrometre resolution, finer structures, which are required for the optical response, will be obtained after infiltration of the written porous pepper-pot structure with cellulose and chitin from solution. They will form polysaccharide membranes covering the pores and the final active structure will be obtained in a self-assembly process including controlled rupture. We will also develop chemical synthesis routes to novel polysaccharide based compounds, which can be used in DLW. This allows us to generate the basic pepper-pot all from polysaccharides (as in natural systems).

Additionally, the self-organisation capabilities of the polysaccharide are necessary for tailoring the degree of disorder in such structures. Finally, a model device will be manufactured from the results of each individual work package, where we can evaluate the underlying optical principles and refer them to the introduced degree of disorder. Our approach basically combines inspiration from biology with a materials engineering approach and chemical synthetic and physical methods for the design of novel optical structured, which gain their function from a tailor-made degree of disorder.

Contributors

  • Prof. Cordt Zollfrank
  • Prof. Georg von Freymann
  • Marie-Christin Angermann