Triboelectric wetting for continuous droplet transport

Abstract

Manipulating liquid is of great significance in fields from life sciences to industrial applications. Owing to its advantages in manipulating liquids with high precision and flexibility, electrowetting on dielectric (EWOD) has been widely used in various applications. Despite this, its efficient operation generally needs electrode arrays and sophisticated circuit control. Here, we develop a largely unexplored triboelectric wetting (TEW) phenomenon that can directly exploit the triboelectric charges to achieve the programmed and precise water droplet control. This key feature lies in the rational design of a chemical molecular layer that can generate and store triboelectric charges through agile triboelectrification. The TEW eliminates the requirement of the electric circuit design and additional source input and allows for manipulating liquids of various compositions, volumes, and arrays on various substrates in a controllable manner. This previously unexplored wetting mechanism and control strategy will find diverse applications ranging from controllable chemical reactions to surface defogging.

Unidirectional Droplet Propulsion onto Gradient Brushes without External Energy Supply

“…Other possibilities of directional motion can take advantage of charge gradients that can achieve long-range transport and are based on electrostatic 31,32 or triboelectric charges. 33 In contrast, motion caused by temperature gradient (thermotaxis), 34 electrical current, 35−38 charge, 39−41 or even simple stretch, 42 would require external energy supply, 19 as, also, in the case of chemically driven droplets, 43,44 droplets on vibrated substrates, 45−48 or wettability ratchets. 49−52 Inspired by our previous work with specific substrate designs that lead to the durotaxis 13 and rugotaxis 24 motion of nanodroplets as motivated by the corresponding experiments, 15,25 here, we propose a new design for the substrate, which is capable of sustaining the droplet motion.…”

“…In the latter case, the motion can take place in one or the other direction, depending on the surface tension of the liquid. Other possibilities of directional motion can take advantage of charge gradients that can achieve long-range transport and are based on electrostatic , or triboelectric charges . In contrast, motion caused by temperature gradient (thermotaxis), electrical current, − charge, − or even simple stretch, would require external energy supply, as, also, in the case of chemically driven droplets, , droplets on vibrated substrates, − or wettability ratchets. − …”

Noncontact Charge Shielding Knife for Liquid Microfluidics

“…According to the above-mentioned simulation, two droplets that have been divided can naturally carry opposite charges due to polarization of the droplets caused by the potential gradient. , Thus, droplets with different charges exhibit quite distinct motion styles under actuation of the CSM platform.…”

Charge-Powered Electrotaxis for Versatile Droplet Manipulation

“…Accordingly, introducing the external force source, such as electricity, to actively evoke the taxis property of droplets might be a more promising means for droplet manipulation. Various electricity-based strategies, such as electrowetting, , electrodewetting, dielectrophoresis, − surface charge printing, , Coulomb attraction/repulsion, − and so on, − have been widely used in droplet manipulation. Despite great improvement in droplet manipulating performance, these methods still suffer from several limitations, such as the complexity of the manipulation platform, instability of droplet motion, and so on.…”