Kim Minji, Kim Jong Bin, Kim Shin-Hyun
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141 Republic of Korea.
Microsyst Nanoeng. 2024 Jan 31;10:21. doi: 10.1038/s41378-024-00651-2. eCollection 2024.
Colloidal crystallization serves as one of the most economic and scalable production methods for photonic crystals. However, insufficient optical performance, nonuniformity and low reproducibility remain challenges for advanced high-value applications. In this study, we optimally formulate a photocurable dispersion of silica particles and apply shear flow to unify the orientation of the colloidal crystals, ensuring high optical performance and uniformity. The silica particles experience strong repulsion at ultrahigh volume fractions of 50% but demonstrate low mobility, leading to polycrystalline structures. Applying shear flow to the dispersions allows the silica particles to rearrange into larger crystalline domains with a unidirectional orientation along the flow. This shear-induced structural change produces absolute reflectivity at the stopband as high as 90% and a high transparency of 90% at off-resonant wavelengths with minimal diffusive scattering. Furthermore, the strong interparticle repulsion ensures a uniform volume fraction of particles throughout the dispersion, reducing deviations in the optical properties. We intricately micropattern the photocurable dispersions using photolithography. Additionally, the photonic films and patterns can be stacked to form multiple layers, displaying mixed structural colors and multiple reflectance peaks without sacrificing reflectivity. These superior photonic materials hold promise for various optical applications, including optical components and anticounterfeiting patches.
胶体结晶是光子晶体最经济且可扩展的生产方法之一。然而,对于先进的高价值应用而言,光学性能不足、不均匀性和低再现性仍然是挑战。在本研究中,我们优化配制了二氧化硅颗粒的光固化分散体,并施加剪切流以使胶体晶体的取向统一,从而确保高光学性能和均匀性。二氧化硅颗粒在50%的超高体积分数下会经历强烈排斥,但迁移率较低,导致形成多晶结构。对分散体施加剪切流可使二氧化硅颗粒重新排列成更大的晶域,沿流动方向具有单向取向。这种剪切诱导的结构变化在阻带处产生高达90%的绝对反射率,在非共振波长处具有90%的高透明度,且漫散射极小。此外,强烈的颗粒间排斥确保了整个分散体中颗粒的体积分数均匀,减少了光学性能的偏差。我们使用光刻技术对光固化分散体进行精细的微图案化。此外,光子薄膜和图案可以堆叠形成多层,呈现混合结构颜色和多个反射峰,而不会牺牲反射率。这些优异的光子材料在包括光学元件和防伪贴片在内的各种光学应用中具有广阔前景。