Superabsorbent hydrogels are significant not only in materials science but also in industries and daily life, being used in diapers or soil conditioners as typical examples. The main feature of these materials is their capacity to hold considerable amount of water, which is strongly dependent on the cross-linking density. This study focuses on the preparation of hydrogels by reweighing the effect of cross-linking density on physical properties, which provides green fabrication of bilayered hydrogels that consist of homogeneous structural motifs but show programmed responses via sequential radical polymerization. In particular, when two hydrogel layers containing different cross-linking densities are joined together, an integrated linear bilayer shows heterogeneous deformation triggered by water. We monitor the linear hydrogel bilayer bending into a circle and engineer it by incorporating disperse dyes, changing colors as well as physical properties. In addition, we demonstrate an electric circuit switch using a patterned hydrogel. Anisotropic shape change of the polyelectrolyte switch closes an open circuit and lights a light-emitting diode in red. This proposed fabrication and engineering can be expanded to other superabsorbent systems and create smart responses in cross-linked systems for biomedical or environmental applications.

中文翻译：

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双层水凝胶的快速制造和工程：重新审视超吸水性聚丙烯酸的交联效应。

超吸水性水凝胶不仅在材料科学中具有重要意义，而且在工业和日常生活中也具有重要意义，典型例子是用于尿布或土壤改良剂。这些材料的主要特征是它们能够容纳大量的水，这在很大程度上取决于交联密度。这项研究的重点是通过重新权衡交联密度对物理性质的影响来制备水凝胶，这提供了双层水凝胶的绿色制造，该双层水凝胶由均质结构图案组成，但通过顺序自由基聚合显示出程序化响应。特别是，当两个含有不同交联密度的水凝胶层连接在一起时，集成的线性双层表现出由水引发的异质变形。我们监测线性水凝胶双层弯曲成圆形的过程，并通过加入分散染料、改变颜色和物理特性来对其进行设计。此外，我们还演示了使用图案化水凝胶的电路开关。聚电解质开关的各向异性形状变化闭合开路并点亮红色发光二极管。这种提出的制造和工程可以扩展到其他超吸收性系统，并在生物医学或环境应用的交联系统中创建智能响应。