Decreasing the Saturated Contact Angle in Electrowetting‐on‐Dielectrics by Controlling the Charge Trapping at Liquid–Solid Interfaces

Abstract

Contact angle saturation in electrowetting‐on‐dielectrics (EWOD) has restricted the tuning range of the wettability of a solid surface, which has generally limited the performances of EWOD devices such as digital microfluidics, lab‐on‐chip, electronic displays, and so forth. Here, a method is proposed for decreasing the saturated contact angle by controlling the behavior of charge trapping at the liquid–solid interface. An unexpected phenomenon is uncovered: for a short time the contact angle reaches smaller values before it retreats to its saturation value, which is caused by charge trapping at the liquid–solid interface. Experimental results suggest that the trapped charges can be repeatedly detrapped and retrapped when the polarity of the applied voltage is periodically reversed, which results in contact angles retreating periodically. By applying a well‐modulated voltage signal with reversing polarity, the retreat movement of the contact angle can be controlled to obtain a value significantly smaller than the previously possible threshold. As a specific application of this method, an economic two‐step process which is developed potentially suitable for mass‐producing large‐area flexible microlens arrays with controllable curvatures and wide fields of view.

Electrodeposited surfaces with reversibly switching interfacial properties

“…Under a negative electrical potential, the dodecyl chain tails will be positively charged ( Fig. 3B) (36). Therefore, the positively charged dodecyl chain tails will move toward the negatively charged silver porous membrane, achieving orientation change of the dodecyl chain tails (Fig.…”

Microlens arrays with adjustable aspect ratio fabricated by electrowetting and their application to correlated color temperature tunable light-emitting diodes

“…3(b need time to migrate in reverse. Before the charges finish migrating, the reverse electric field and the external electric field form a short-term codirectional superposition, making the electric field stronger than in the saturated state [53]. Under a certain frequency of reversing, the superposition electric field can maintain a stable value that is higher than the pristine saturation voltage, so the contour curvature formed under the square wave voltage condition is larger.…”

A portable driving system for high‐resolution active matrix electrowetting display based on FPGA

“…This negative behavior of EWD is called “backflow” which may lead to the stability degradation of EWD. Some scholars have found that charge trapping is one reason for backflow. Fig .…”

“…This negative behavior of EWD is called "backflow" which may lead to the stability degradation of EWD. Some scholars have found that charge trapping is one reason for backflow 15,16 . Fig.3 illustrates the charge trapping phenomenon of EWD by plotting reflectivity as a function of time in red dotted line.…”