Electrically controlled localized charge trapping at amorphous fluoropolymer-electrolyte interfaces

TL;DR

This study investigates microscopic charge trapping at amorphous fluoropolymer-electrolyte interfaces in electrowetting devices, revealing localized charge regions and proposing a low-cost method for stable charge deposition.

Contribution

It demonstrates localized charge trapping at the three-phase contact line and introduces a simple method to deposit stable charges on fluoropolymer surfaces.

Findings

Localized charge trapping at the contact line region.

Charge densities up to 0.46 mC/m2 achieved.

Negative charges remain stable after harsh testing.

Abstract

Charge trapping is a long-standing problem in electrowetting-on-dielectric (EWOD), causing reliability reduction and restricting its practical applications. Although this phenomenon has been investigated macroscopically, the microscopic investigations are still lacking. In this work, the trapped charges are proven to be localized at three-phase contact line region by using three detecting methods -- local contact angle measurements, electrowetting (EW) probe, and Kelvin Probe Force Microscopy (KPFM). Moreover, we demonstrate that this EW-induced charge trapping phenomenon can be utilized as a simple and low-cost method to deposit charges on fluoropolymer surfaces. Charge density near the three-phase contact line up to 0.46 mC/m2 and the line width with deposited charges ranging from 20 to 300 micrometer are achieved by the proposed method. Particularly, negative charge densities do not degrade even after harsh testing with a water droplet on top of the sample surfaces for 12 hours, as well as after being treated by water vapor for 3 hours. These findings provide an approach for applications which desire stable and controllable surface charges.