Electric-field induced droplet vertical vibration and horizontal motion: Experiments and simulations

TL;DR

This study explores droplet manipulation using electrowetting and electrostatic induction, demonstrating vertical vibrations and horizontal motion through experiments and simulations, with insights into voltage effects and surface energy interactions.

Contribution

It introduces a novel combined approach for droplet control using EWOD and ESI, including a theoretical model for vibration morphology and analysis of horizontal motion.

Findings

Vertical droplet vibrations induced by EWOD with saturation at 120 V.

Horizontal droplet motion achieved at voltages below 1000 V.

Surface energy analysis links contact angle saturation to vibration amplitude.

Abstract

In this work, Electrowetting on Dielectric (EWOD) and electrostatic induction (ESI) are employed to manipulate droplet on the PDMS-ITO substrate. Firstly, we report large vertical vibrations of the droplet, induced by EWOD, within a voltage range of 40 to 260 V. The droplet's transition from a vibrating state to a static equilibrium state are investigated in detail. It is indicated that the contact angle changes synchronously with voltage during the vibration. The electric signal in the circuit is measured to analyze the vibration state that varies with time. By studying the influence of driving voltage on the contact angle and the amplitude in the vibration, it is shown that the saturation voltage of both contact angle and amplitude is about 120 V. The intrinsic connection between contact angle saturation and amplitude saturation is clarified by studying the surface energy of the droplet. A theoretical model is constructed to numerically simulate the vibration morphology and amplitude of the droplet. Secondly, we realize the horizontal motion of droplets by ESI at the voltage less than 1000 V. The charge and electric force on the droplet are numerically calculated. The frictional resistance coefficients of the droplet are determined by the deceleration of the droplet. Under consideration of frictional resistance of the substrate and viscous resistance of the liquid, the motion of the droplet is calculated at 400 V and 1000 V, respectively. This work introduces a new method for manipulating various forms of droplet motion using the single apparatus.