We have developed a hygromorphic metal oxide actuator using an electrochemical method to produce a superhydrophilic free-standing nano-capillary forest of titanium oxide with a high aspect ratio (~80). This metal oxide film has an inhomogeneous initial gap at the top and bottom surfaces between the tubes due to flexure during fabrication. The actuation mechanism is as follows. First, when a drop of water is applied on the surface of a titanium oxide nano-capillary forest (TNF), the water penetrates through the film instantaneously, and the titanium oxide nano-capillaries are pulled together by interplay of the capillary force and van der Waals force. When water has fully filled in the gaps between the capillaries, the free-standing TNF film remains unbent for ~2 min. Then, as the water evaporates, the film bends further in the forward direction. When the water has completely evaporated, the van der Waals force alone acts on the capillaries, and the TNF film returns to its initial state. This TNF possesses great stability and repeatability for long-term usage having a high bending energy density of ~1250 kJ m^–3 and unique capabilities. It may lead to novel stimuli-responsive systems, including energy collection and storage, as well as robotics applications.

我们已经开发出了一种使用电化学方法的吸湿性金属氧化物致动器，以生产出具有高长宽比（〜80）的超亲水性纳米氧化钛自支撑纳米毛细森林。由于制造过程中的挠曲，该金属氧化物膜在管之间的顶面和底面具有不均匀的初始间隙。致动机制如下。首先，将一滴水滴涂在二氧化钛纳米毛细管森林（TNF）的表面上时，水会瞬间穿透膜，并且二氧化钛纳米毛细管通过毛细作用力和范本的相互作用而被拉在一起。德华力。当水完全填充在毛细血管之间的缝隙中时，独立的TNF膜在约2分钟内保持不弯曲。然后，随着水的蒸发，薄膜进一步向前弯曲。当水完全蒸发后，范德华力仅作用在毛细管上，而TNF膜又回到其初始状态。该TNF具有很高的稳定性和可重复性，可长期使用，弯曲能量密度高达〜1250 kJ m^–3和独特的功能。它可能会导致新型的刺激响应系统，包括能量收集和存储以及机器人应用。