Programmable functional surfaces face a tradeoff between fast reprogrammability and stable self-maintainability. The integration of field-responsive materials offers convenience for repeated programming of functional surfaces but necessitates continuous energy input to maintain the programmed functions. Meanwhile, technologies such as shape memory and functional coatings enable stable maintenance of surface states but result in a time-consuming reprogramming process. This tradeoff limits the demonstration of surface properties. We present a magnetic mini flap (at the millimeter scale) that can self-maintain its surface state and a pulsed magnetic tip to enable local fast reprogramming of the mini flaps within 100 ms. The mini flaps are arranged in a pixel array, where each pixel can be customized for specific surface properties, such as wettability and reflectivity.
The dynamic surface self-reconstruction behavior in local structure correlates with oxygen evolution reaction (OER) performance, which has become an effective strategy for constructing the catalytic active phase. However, it remains a challenge to understand the mechanisms of reconstruction and to accomplish it fast and deeply. Here, we reported a photo-promoted rapid reconstruction (PRR) process on Ag nanoparticle-loaded amorphous Ni-Fe hydroxide nanosheets on carbon cloth for enhanced OER. The photogenerated holes generated by Ag in conjunction with the anodic potential contributed to a thorough reconstruction of the amorphous substrate. The valence state of unsaturated coordinated Fe atoms, which serve as active sites, is significantly increased, while the corresponding crystalline substrate shows little change. The different structural evolutions of amorphous and crystalline substrates during reconstruction lead to diverse pathways of OER. This PRR utilizing loaded noble metal nanoparticles can accelerate the generation of active species in the substrate and increase the electrical conductivity, which provides a new inspiration to develop efficient catalysts via reconstruction strategies.
Michell's instability, a classic type of mechanical instability, has received tremendous interest from different disciplines. It occurs when the pre-torsion in an elastic ring surpasses a critical value; the elastic ring spontaneously undergoes a transition from a flat or warped shape to a figure-of-eight configuration. However, such instability has rarely been exploited in designing soft actuators. Here, by employing a stimulus-triggered Michell's instability, hydrogel-based ring actuators capable of fast shape morphing are developed. Upon heating or light irradiation, the hydrogel ring transforms rapidly from the saddle-shape into the figure-of-eight configuration. Rigorous experiments and simulations reveal the underlying mechanism and attribute it to the stimuli-induced variations in bending and torsional stiffnesses of the gel string with anisotropic structure and response, which reduces the critical twist for Michell's instability of the ring actuator. Moreover, effects of light intensity, environmental temperature, ring size, and pre-torsion on reconfiguration are also investigated. The fast action of the ring actuators in aqueous conditions has been demonstrated through various tasks, such as screwing a bottle cap, kicking a ball, and triggering synergetic deformations. The design principle of soft actuators by harnessing Michell's instability should merit the development of other soft machines with fast action and large-amplitude reconfiguration.
危险品化学品经营许可证（带存储）