Bigdeli Masoud Bozorg, Tsai Peichun Amy
Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G8, Canada.
Langmuir. 2020 May 5;36(17):4835-4841. doi: 10.1021/acs.langmuir.0c00193. Epub 2020 Apr 20.
We employed a convenient evaporation approach to fabricate photonic crystals by naturally drying droplets laden with nanoparticles on a superhydrophobic surface. The final drying morphology could be controlled by the concentration of nanoparticles. A dilute droplet resulted in a torus, whereas a quasi-spherical cap with a bottom cavity was made from a concentrated droplet. Remarkably, the nanofluid droplets maintained high contact angles (≳120°) during the entire evaporation process because of inhomogeneous surface wetting. Bottom-view snapshots revealed that during evaporation the color of the contact area changed sequentially from white to red, orange, yellow, and eventually to green. Scanning electron microscopy and Voronoi analysis demonstrated that nanoparticles were self-assembled to a hexagonal pattern. Finally, based on the effects of particle size, material, and volume concentration on the reflected wavelengths, a model has been developed to successfully predict the reflected wavelength peaks from the contact area of evaporating colloidal droplets. Our model can be easily adopted as a manufacturing guide for functional photonic crystals to predict the optimal reflected color made by evaporation-driven self-assembly of photonic crystals.
我们采用了一种简便的蒸发方法，通过在超疏水表面自然干燥负载纳米颗粒的液滴来制备光子晶体。最终的干燥形态可通过纳米颗粒的浓度来控制。稀液滴会形成一个圆环，而浓液滴则会形成一个带有底部空腔的准球形帽。值得注意的是，由于表面润湿性不均匀，纳米流体液滴在整个蒸发过程中保持着高接触角（≳120°）。底视图快照显示，在蒸发过程中，接触区域的颜色依次从白色变为红色、橙色、黄色，最终变为绿色。扫描电子显微镜和Voronoi分析表明，纳米颗粒自组装成六边形图案。最后，基于粒径、材料和体积浓度对反射波长的影响，开发了一个模型，成功预测了蒸发胶体液滴接触区域的反射波长峰值。我们的模型可以很容易地用作功能性光子晶体的制造指南，以预测由光子晶体蒸发驱动自组装产生的最佳反射颜色。
