Continuous electrowetting via electrochemical diodes

Abstract

We describe a novel method for droplet transport combining electrowetting on dielectric (EWOD) and the diode-like behavior of valve metals to achieve unique actuation performance. While traditional EWOD droplet transport requires switching of voltage between multiple electrodes, our method, which we term continuous rectified electrowetting, utilizes a simple single electrode and a DC voltage to move a 50 μl droplet 28 mm with velocities up to 32 mm s(-1).

Open-loop electrowetting actuation with micro-stepping

“…While most applications focus on the movement of droplets or liquid interfaces [8], droplets have also been 2 used to perform out of plane mechanical actuation as an alternative to electrostatic actuation [9] as well as both linear and rotational in-plane motions [10,11]. Continuous motion similar to electromechanical motors was demonstrated using metallic droplets and using embedded diodes.Continuous motion similar to electromechanical motors was demonstrated using metallic droplets [10] and using embedded diodes [12]. However, the majority of EWOD actuation is done in open-loop stepped systems analogous to a stepper motor.…”

“…We have reported on a bi-directional electrowetting scheme which induces a polarity dependence [24] in the EW response through the use of a passivating conductive layer (aluminum, titanium) and an adaption that uses only two electrode pads to continuously move a droplet with a DC voltage input [12]. Using a thin dielectric with inherent defects, the electrolyte/electrode interface rapidly forms and dissolves a thin oxide on metals such as aluminum and titanium for anodic and cathodic polarization respectively.…”

“…Although both the continuous pumping and step actuation methods are based on electrochemical diodes, the droplet in the continuous actuation system was actuated as a linear motor with constant voltage input [12]. In this paper, asymmetric AC signals are used to create a stepper motor with microstepping.…”

“…In the present case coplanar electrodes are uniformly coated with a leaky dielectric over a passivating electrode. Electrically, this system is best modeled as two diodes in series similar to prior work with DC voltages [12,23,24,25]. This work considers the impact of AC inputs.…”

Floating electrode electrowetting on hydrophobic dielectric with an SiO2 layer

“…Other configurations are possible, including grounding from below [4][5] , bi-directional and continuous electrowetting [6][7] . The wetting angle is given by the Lippmann equation: Here, θ 0 and θ 1 are the angles before and after electric field application, V is the applied voltage, γ LO is the droplet/second phase surface energy (air in this case), δ is the dielectric thickness, and ε 0 ε r is the dielectric permittivity.…”