State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, 311215, China.
Nat Commun. 2021 Oct 25;12(1):6155. doi: 10.1038/s41467-021-26464-9.
Far-from-equilibrium (FFE) conditions give rise to many unusual phenomena in nature. In contrast, synthetic shape-shifting materials typically rely on monotonic evolution between equilibrium states, limiting inherently the richness of the shape-shifting behaviors. Here we report an unanticipated shape-shifting behavior for a hydrogel that can be programmed to operate FFE-like behavior. During its temperature triggered shape-shifting event, the programmed stress induces uneven water diffusion, which pushes the hydrogel off the equilibrium based natural pathway. The resulting geometric change enhances the diffusion contrast in return, creating a self-amplifying sequence that drives the system into an FFE condition. Consequently, the hydrogel exhibits counterintuitive two opposite shape-shifting events under one single stimulation, at a speed accelerated by more than one order magnitude. Our discovery points to a future direction in creating FFE conditions to access otherwise unattainable shape-shifting behaviors, with potential implications for many engineering applications including soft robotics and medical devices.
远离平衡（FFE）条件在自然界中产生了许多不寻常的现象。相比之下，合成形状记忆材料通常依赖于平衡状态之间的单调演变，这限制了形状记忆行为的固有丰富性。在这里，我们报告了一种水凝胶的意外形状记忆行为，该水凝胶可以被编程为实现 FFE 样行为。在其温度触发的形状记忆事件中，编程的应力会引起不均匀的水扩散，从而将水凝胶推出基于平衡的自然途径。由此产生的几何形状变化反过来增强了扩散对比度，形成一个自我增强的序列，将系统推向 FFE 条件。结果，水凝胶在单一刺激下表现出两种相反的、违背直觉的形状记忆行为，其速度比一个数量级快。我们的发现为创造 FFE 条件以获得其他无法实现的形状记忆行为指明了一个未来的方向，这对于许多工程应用具有潜在的影响，包括软机器人和医疗器械。
