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

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The intricate photonic structures found in the scales of white beetles are a paradigm for tailored disorder in nature: the scattering strength has been optimized with respect to the low available refractive index contrast, the weight of the structure, its volume as well as its stability. These properties are static, however. Nature also excels in systems, which adjust their shape or other properties depending on external stimuli like humidity or temperature. We want to use this self-actuation in this project, to derive artificial photonic materials, which change their properties under external stimuli. We start with our cellulose-based photoresist and extend it to the poly-saccharide chitin. Via three-dimensional laserlithography we fabricate strong scattering structures from these materials. As blueprint we use a model developed by us, which follows the construction principle of the white beetle’s scales. Embedding swellable materials into the structures (e.g. cellulose spheres), critical dimensions can be tuned in dependence of humidity. This allows us to switch the material from a nearly transparent state (collapsed material, strong optical crowding) to a highly scattering state (open structure). Our approach might open the way to bio-based materials, whose optical properties can be controlled by external stimuli.