Colloidal crystals have been used for creating stimuli‐responsive photonic materials. Here, macroporous hydrogels are designed, through a simple and reproducible protocol, that rapidly and reversibly switch between highly transparent and structurally colored states. The macroporous hydrogels are prepared by film‐casting photocurable dispersions of silica particles in hydrogel‐forming resins and selectively removing silica particles. The silica particles spontaneously form a nonclose‐packed array due to repulsive interparticle interaction, which form the regular array of cavities after removal. However, the cavities are randomly collapsed by drying, losing a long‐range order and rendering the materials highly transparent. When the hydrogels are swollen by either water, ethanol, or the mixture, the regular array is restored, which develops brilliant structural colors. This switching is completed in tens of seconds and repeatable without any hysteresis. The resonant wavelength depends on the composition of the water–ethanol mixture, where the dramatic shift occurs in one‐component‐rich mixtures due to the composition of the hydrogel. Micropatterns can be designed to have distinct domains of the macroporous hydrogels, which are transparent at the dried state and disclose encrypted graphics and unique reflectance spectra at the wet state. This class of solvent‐responsive photonic hydrogels is potentially useful for alcohol sensors and user‐interactive anti‐counterfeiting materials.

中文翻译：

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大孔水凝胶可在透明状态和结构着色状态之间快速且可逆地转换

胶体晶体已用于产生刺激响应的光子材料。在这里，大孔水凝胶是通过简单且可重现的协议设计的，可在高透明状态和结构着色状态之间快速且可逆地切换。大孔水凝胶的制备方法是，将二氧化硅颗粒的光固化分散体薄膜浇铸在形成水凝胶的树脂中，然后选择性地除去二氧化硅颗粒。由于排斥性的颗粒间相互作用，二氧化硅颗粒自发地形成了一个非密排阵列，在去除后形成了规则的腔阵列。但是，空腔会因干燥而随机塌陷，失去长期秩序，并使材料高度透明。当水凝胶被水，乙醇或混合物溶胀时，规则排列会恢复，形成鲜艳的结构色彩。此切换在数十秒内完成，并且可重复执行而没有任何滞后。共振波长取决于水-乙醇混合物的组成，其中由于水凝胶的组成，在富含单组分的混合物中会发生剧烈变化。可以将微图案设计为具有大孔水凝胶的不同区域，这些区域在干燥状态下是透明的，并公开了加密的图形和在潮湿状态下的独特反射光谱。这类对溶剂敏感的光子水凝胶可用于酒精传感器和用户互动的防伪材料。由于水凝胶的组成，在富含单组分的混合物中发生了巨大变化。可以将微图案设计为具有大孔水凝胶的不同区域，这些区域在干燥状态下是透明的，并公开了加密的图形和在潮湿状态下的独特反射光谱。这类对溶剂敏感的光子水凝胶可用于酒精传感器和用户互动的防伪材料。由于水凝胶的组成，在富含单组分的混合物中发生了巨大变化。可以将微图案设计为具有大孔水凝胶的不同区域，这些区域在干燥状态下是透明的，并在湿状态下公开加密的图形和独特的反射光谱。这类对溶剂敏感的光子水凝胶可用于酒精传感器和用户互动的防伪材料。