Moving water droplets induced electricity on an electret surface with a charge gradient

In solid-liquid systems, a variety of electrokinetic effects can generate electricity utilizing diverse forms of gradients, for instance, pressure and salinity gradients. Here we report a new electrokinetic effect that moving a water droplet on an electret surface with a charge gradient can induce electricity in circuit between the droplet and an electrode underneath the electret film. While the droplet moves along the charge gradient, electric double layers at the solid-liquid interfaces continue to be charged or discharged through the circuit due to the change in surface charge density, leading to a direct-current output that can be quantitatively described by a proposed model. Furthermore, the direct correlation between the electrical output and the surface charge gradient endows the droplet with intelligence to sense the surface charge distribution, and the read of binary digital information stored in a charge matrix using a tiny water droplet was achieved. The reported electrokinetic effect not only promises a new sustainable avenue to deliver application-friendly direct-current electricity, distinct from the instantaneous pulsed output of traditional devices, but also extends the intelligent functionality of water droplets.

Automated summary

This research reports a new electrokinetic effect that generates electricity between a water droplet and an electrode by utilizing a charge gradient, and the direct correlation between the electrical output and the surface charge gradient allows the water droplet to sense and read stored information.