Non-Hookean Droplet Spring for Enhancing Hydropower Harvest.

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.