Molecular Investigation of Contact Line Movement in Electrowetted Nanodroplets

Abstract

Molecular dynamics (MD) simulation of an electrowetted nanodroplet is performed to understand the fundamental origin of the involved parameters resulted from the molecular movement in the vicinity of the three-phase contact line (TPCL). During the spreading of the droplet, contact line friction (CLF) force is found to be the controlling one among all other resistive forces. Being molecular in nature, MD study is required to unveil the CLF, which is manifested by the TPCL friction coefficient ζ. The combined effect of temperature, electric field, and surface wettability, manifested by the solid–liquid Lennard-Jones interaction parameter, is studied to explore the droplet spreading. The entire droplet wetting dynamics is divided into two different regimes, namely, spreading regime and equilibrium regime. The molecular frequency during the TPCL movement in the equilibrium regime is affected by the presence of any external perturbation and results in an alteration of ζ. The predetermined knowledge of the alteration of CLF due to the coupling effect of electric field and temperature will have a potential application towards designing electric field-inspired droplet movement devices.

Molecular Investigation of the Actuation of Electrowetted Nanodroplets

“…Other parameters for interactions with hydrogen were set to zero. A cutoff length of 10 Å was used for electrostatic and van der Waals forces based on the guidelines laid out by Chen et al Several prior MD simulation studies ,, of electrowetting of nano-sized droplet have used a similar cutoff to account for electrostatic forces. Lorentz–Berthelot mixing rules , were used to calculate any unknown coefficients.…”

“…In the presence of a continuous electric field, a droplet resting on a large path would attain an equilibrium configuration that may or may not be asymmetric. This has been extensively explored in prior studies. − Daub et al concluded that the contact angle of a droplet in the presence of perpendicular and parallel electric fields is highly sensitive to the direction and polarity of the field. Song et al , later concluded that the asymmetry in the contact angles vanishes beyond a certain field strength.…”

“…Several MD simulation-based studies have been used to perform simulations of spreading dynamics, ,, evaporation, and coalescence. − In a study conducted by Chen et al, initial dynamics of electrospreading of droplets in the presence of a perpendicular electric field was realized using MD simulations and found to result in comparable trends against experimental findings. More recent studies have revealed the role of the contact line friction (CLF) , and the wetting dynamics of nanoscale droplets in presence of electric fields . Hao et al .…”

“…reported that smooth and tunable response of droplets undergoing EWOD can be limited by contact line pinning, which can be suppressed through electrowetting-on-liquid-infused film (EWOLF). Investigations of the alteration in the line friction of electrowetted nano-sized water droplets have established retardation of spreading induced by the application of an electric field. , There are a few MD simulation studies ,, on electrowetting at the nanoscale that have explored the droplet spreading dynamics commonly encountered in a typical electrowetting setup. The actuation of nanoscale droplets across an array of electrodes is ubiquitous in a number of critical applications requiring rapid and precise manipulation of droplets.…”

Controllable Flowing of a Dielectric Fluid Droplet under the Action of Corona Discharge

“…Compared with solids, fluids are flexible and easy to control. The control of fluid movement, fusion, separation, and surface morphology is widely used in many fields, such as chemistry, biology, medicine, micro-electromechanical manufacturing, and so on. − The most traditional way to control fluids is to provide pressure from the outside. There are many methods to control the micro-multiphase fluid in microfluidic technology, mainly including the passive mode and active mode.…”