Non‐Hookean Droplet Spring for Enhancing Hydropower Harvest

Abstract

Nonlinear elastic materials are significant for engineering and micromechanics. Droplets with the merits of easy‐accessibility, diversity, and energy‐absorption capability exhibit a variety of non‐Hookean elastic behaviors. Herein, benefiting from the confinement of heterogeneous‐wettable parallel plates, the non‐Hookean mechanics of the droplet‐based spring are systematically investigated. Experimental results and theoretical analysis reveal that the force generated by the spring varies nonlinearly with its deformation, and a force model is accordingly built to depict the mechanics of springs with different sized/numbered droplets and confined by different wettability patterns. Importantly, for the droplet‐based spring, the droplet‐plate contact area expands nonlinearly with the pressing force, which is employed to optimize the output performance of the droplet‐based triboelectric nanogenerator to 226% compared with the control test. This finding deepens the understanding of the non‐Hookean behavior of droplet‐based springs, and sheds light on applications in energy harvesting, micromechanics, and miniature optic/electric devices.

A droplet‐based electricity generator with ultrahigh instantaneous output and short charging time

“…In summary, leveraging a systematical optimization in the dielectric layer thickness, droplet ion concentration, and external load, we achieved a DEG with ultrahigh instantaneous output and short charging time. In the future, it is essential to develop ideal and scalable dielectric materials featuring high charge storage capability and propose new design architecture to further advance the output performances of DEG 48–55 . We envision that the working mechanism and circuit model we proposed in this study will provide important insights for liquid energy harvesting.…”

“…In the future, it is essential to develop ideal and scalable dielectric materials featuring high charge storage capability and propose new design architecture to further advance the output performances of DEG. [48][49][50][51][52][53][54][55] We envision that the working mechanism and circuit model we proposed in this will provide important insights for liquid energy harvesting.…”

Electrification of water: From basics to applications

“…Such a process drives electron flow through external circuits, thereby generating electricity, and this strategy is usually referred to as droplet‐based triboelectric nanogenerators 16,58,59 . In addition to the contact state variation‐induced contact electrification, the change of contact area or lines can induce the capacitance change of an EDL‐based capacitor, and here, EDL is regarded as a capacitor because of the configuration of two parallel layers in EDL formed at the solid/liquid interface with opposite polarity 60–62 . One typical method to ensure the change of contact area to generate electrical energy is shown in Figure 3b, where one water droplet bridging two parallel surfaces with different wettabilities can be regarded as top and bottom capacitors 60 .…”

“…One typical method to ensure the change of contact area to generate electrical energy is shown in Figure 3b, where one water droplet bridging two parallel surfaces with different wettabilities can be regarded as top and bottom capacitors 60 . By vertically oscillating the top surface, the continuous variation of capacitance on top capacitors can output electrical energy 60,61 . Similarly, mechanically‐actuated change of the contact region at the water/solid interface can result in the disruption of the initial charge balance at the water/solid interface created by an external electric bias, which can output electrical energy 63 .…”

Water Droplet‐Based Nanogenerators

“…[155,156] Xue et al have deployed a water droplet into a spring system to fabricate a droplet-based TENG that can be applied to micromechanics, and miniature optical/electrical devices. [157] The current research status of these droplet-based nanogenerators indicates a promising future in future for energy harvesting and self-powered sensor networks.…”