Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91, Stockholm, Sweden.
Department of Materials and Environmental Chemistry, Wallenberg Wood Science Center, Stockholm University, SE-10691, Stockholm, Sweden.
Nat Commun. 2023 May 29;14(1):3099. doi: 10.1038/s41467-023-38819-5.
Photonic crystals are optical materials that are often fabricated by assembly of particles into periodically arranged structures. However, assembly of lignin nanoparticles has been limited due to lacking methods and incomplete understanding of the interparticle forces and packing mechanisms. Here we show a centrifugation-assisted fabrication of photonic crystals with rainbow structural colors emitted from the structure covering the entire visible spectrum. Our results show that centrifugation is crucial for the formation of lignin photonic crystals, because assembly of lignin nanoparticles without centrifugation assistance leads to the formation of stripe patterns rather than photonic crystals. We further prove that the functions of centrifugation are to classify lignin nanoparticles according to their particle size and produce monodispersed particle layers that display gradient colors from red to violet. The different layers of lignin nanoparticles were assembled in a way that created semi-closed packing structures, which gave rise to coherent scattering. The diameter of the lignin nanoparticles in each color layer is smaller than that predicted by a modified Bragg's equation. In situ optical microscope images provided additional evidence on the importance of dynamic rearrangement of lignin nanoparticles during their assembly into semi-closed packing structures. The preparation of lignin nanoparticles combined with the methodology for their classification and assembly pave the way for sustainable photonic crystals.
光子晶体是一种光学材料，通常通过将粒子组装成周期性排列的结构来制备。然而，由于缺乏方法和对颗粒间作用力和堆积机制的不完全理解，木质素纳米颗粒的组装受到限制。在这里，我们展示了一种通过离心辅助制备的具有彩虹结构颜色的光子晶体，其结构覆盖整个可见光谱。我们的结果表明，离心对于木质素光子晶体的形成至关重要，因为没有离心辅助的木质素纳米颗粒的组装会导致形成条纹图案而不是光子晶体。我们进一步证明，离心的作用是根据颗粒大小对木质素纳米颗粒进行分类，并产生从红色到紫色的单分散颗粒层，显示出梯度颜色。不同层的木质素纳米颗粒以形成半封闭堆积结构的方式组装，这导致了相干散射。每层木质素纳米颗粒的直径都小于修正布拉格方程预测的值。原位光学显微镜图像提供了更多证据，证明了木质素纳米颗粒在组装成半封闭堆积结构过程中动态重排的重要性。木质素纳米颗粒的制备结合了对其分类和组装的方法，为可持续光子晶体铺平了道路。
