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

在白色甲虫的鳞片中发现的复杂的光子结构是自然界中定制无序的典范：散射强度相对于低可用折射率对比度、结构的重量、体积以及稳定性进行了优化。然而，这些属性是静态的。自然界也擅长于根据湿度或温度等外部刺激来调整它们的形状或其他特性的系统。我们希望在这个项目中利用这种自驱动来获得人造光子材料，这种材料在外部刺激下会改变其性质。我们从以纤维素为基础的光致抗蚀剂开始，并将其扩展到多糖甲壳素。通过三维激光光刻，我们用这些材料制作了强散射结构。作为蓝图，我们使用了我们开发的一个模型，它遵循了白色甲虫鳞片的构造原理。将可膨胀材料嵌入到结构(例如纤维素球)中，可以根据湿度调整关键尺寸。这允许我们将材料从接近透明的状态(坍塌的材料，强烈的光学拥挤)切换到高度散射的状态(开放结构)。我们的方法可能会为基于生物的材料开辟道路，这种材料的光学性质可以通过外部刺激来控制。

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.