Reversible ultralow-voltage liquid–liquid electrowetting without a dielectric layer

Abstract

Electrowetting-on-dielectric devices typically have operating voltages of 10-20 V. A reduction in the operating voltage could greatly reduce the energy consumption of these devices. Herein, fully reversible one-electrolyte electrowetting of a droplet on a solid metal surface is reported for the first time. A reversible change of 29° for an 800 mV step is achieved. The effects of surface roughness, electrolyte composition, electrolyte concentration and droplet composition are investigated. It was found that there is a dramatic dependence of the reversibility and hysteresis of the system on these parameters, contrary to theoretical predictions. When a 3-chloro-1-propanol droplet is used, a system with no hysteresis and a 40° change in angle are obtained.

Electrotunable liquid sulfur microdroplets

“…Therefore, it has been applied in a variety of fields such as micro/ nano-fluidics, adaptive microlenses, etc 10,11 . Normally, a minimum of several tens of volts is required to apply across a dielectric layer to drive these devices 12 . A reduction in the operating voltage could greatly decrease the energy consumption of the whole system due to its voltage-squared dependence.…”

Potential-Controlled Tensiometry: A Tool for Understanding Wetting and Surface Properties of Conductive Powders by Electroimbibition

“…The manipulation of electrostatic and polarization interactions by applying an electric field leads to multiple applications at the solid–liquid interface. Due to the interplay of various types of forces between liquid and solid, electrowetting can be applied in multiple technological fields including liquid lenses, low power displays, microfluidics, DNA analysis and repair, protein recognition, and cell sorting. − In the recent past, the electrowetting processes have been employed for microscale mixing, reaction engineering, energy harvesting and storage, droplet actuation, electronic displays, biomedical engineering, bio-MEMS devices, sensors , and droplet or digital microfluidics . In particular, the hydrodynamic, elastic, and interfacial properties of the dielectric were found to influence the electrowetting of a droplet, while the breakdown voltage is directly related to the thickness of the dielectric. , …”

“…24,25 Few approaches exist to describe spreading of liquids; the so-called electrowetting on dielectric (EWOD) developed in the 1990s has emerged as the most common method in modern analytics. 2,15 However, while this method facilitates an easy handling, there are disadvantages of indirect surface analysis; high voltages are necessary in order to affect the surface charge. Accordingly, other approaches measuring the direct electrowetting on conductive surfaces do exist.…”

“…26,27 Especially the electric double layer forming around the surface and the oxidation state play a crucial role for the wetting properties. 2 While such a direct measurement might therefore affect and possibly alter a surface, it represents the best way of directly and globally analyzing monolayers and functional surface groups on a material. Most often, direct measurements as well as EWOD are conducted as sessile drops on top of the investigated materials, which facilitates an analysis of the drop shape and the contact angle with the surface.…”

“…EWOD devices typically operate at voltages of 10− 20 V while the potential between electrode and liquid in contact is much lower. 2 Increasing potential is supposed to minimize the interfacial tension between the liquid and the substrate, which results in a smaller contact angle of the substrate. Induced charges in the boundary layer affect the interfacial layer and thus the surface free energy.…”