Electrically Controlled Localized Charge Trapping at Amorphous Fluoropolymer–Electrolyte Interfaces

Abstract

Charge trapping is a long-standing problem in electrowetting on dielectric, causing reliability reduction and restricting its practical applications. Although this phenomenon is investigated macroscopically, the microscopic investigations are still lacking. In this work, the trapped charges are proven to be localized at the three-phase contact line (TPCL) region by using three detecting methods-local contact angle measurements, electrowetting (EW) probe, and Kelvin probe force microscopy. Moreover, it is demonstrated that this EW-assisted charge injection (EWCI) process can be utilized as a simple and low-cost method to deposit charges on fluoropolymer surfaces. Charge densities near the TPCL up to 0.46 mC m −2 and line widths of the deposited charge ranging from 20 to 300 µm are achieved by the proposed EWCI method. Particularly, negative charge densities do not degrade even after a "harsh" testing with a water droplet on top of the sample surfaces for 12 h, as well as after being treated by water vapor for 3 h. These findings provide an approach for applications which desire stable and controllable surface charges.

Energy Harvesting from Drops Impacting onto Charged Surfaces

“…The purpose of this Letter is to develop a physical picture and quantitative model of the electrical response caused by the impact of a drop onto an ENG surface based on simultaneous high-speed video imaging and high-speed electrical current measurements. Making use of two recent developments in the literature, namely an improved electrode geometry [6,25] and a robust charging mechanism [25][26][27], we systematically screen a wide range of experimental parameters to validate our model and to derive a scaling relation for the maximum harvested energy. The latter is given by the product of a purely electrostatic (capacitive) contribution and a nondimensional integral that is controlled by fluid dynamic and other process parameters.…”

“…In both cases, the surfaces were coated with an 800 nm to 1000 nm thick film of an amorphous fluoropolymer (AFP; Teflon® AF 1600) [28]. The polymer films were electrically charged prior to the experiment by either dropping more than 500 identical drops onto the surface (indium-tin-oxide samples; surface charge σ s ¼ −0.12; …; 0.16 mC=m 2 ) or by electrowetting-assisted charge injection (EWCI) [26] for the Si wafers (σ s ¼ −0.07; …; −0.35 mC=m 2 ); see Supplemental Material [28], Sec. I for a description of the independent surface charge measurements.…”

Oil Conductivity, Electric-Field-Induced Interfacial Charge Effects, and Their Influence on the Electro-Optical Response of Electrowetting Display Devices

“…Similarly, the significant charge trapped at the oil/FP interface can also cause the reopening effect. The above result suggests that the negative charge is trapped in the FP more significantly than the positive charge [31].…”

A coplanar‐electrode direct‐current triboelectric nanogenerator with facile fabrication and stable output

“…While the metal piece slightly slides on the substrate, the charge distribution on the metal piece will be changed due to electrostatic induction, and more positive charges will move to the rear side of the electrode to balance electrostatic status, generating a unidirectional current from the front side to the rear side of the metal piece ( Figure 1B and Video S1), which can be simulated by commercial software COMSOL as shown in Figure 1C, most of charge is accumulated at both ends of the electrode. 25 In the simulation, we assume that the charge density on dielectric is evenly distributed, and the metal electrode has an equal amount of positive charges. When the electrode slides a little to the rightward, the potential difference between two sides of the electrode will induce the redistribution of the electric charge and generate the current flow.…”