No-contact electrostatic manipulation of droplets on liquid-infused surfaces: Experiments and numerical simulations

Abstract

We propose a simple method of electrostatic manipulation of aqueous droplets sitting on a liquid-infused surface. The electric field is created between a pin electrode not touching the droplets and the grounded substrate. Experiments and numerical simulations are performed to study the sliding of droplets along the surface. Sliding velocities in excess of 1 cm/s can be achieved. The scaling of the sliding velocity with the applied voltage difference and the droplet volume is studied. Good agreement between the experimental and the simulation data indicates that the simulation model captures the essential physics.

Manipulation and control of droplets on surfaces in a homogeneous electric field

“…( 2 ) implies that the droplet is conducting or its relative permittivity approaches infinity, which is a reasonable assumption in the present case. Following the arguments presented in previous work 43 , the thin lubricant film that cloaks the droplet and forms a wetting ridge around the footprint is ignored in our electrostatic model since its contribution is marginal. Instead the cloaking film is adsorbed in an effective interface and the wetting ridge is collapsed into a three-phase contact line (TCL), characterized by an apparent contact angle 37 , 43 .…”

“…The interfacial tensions of the lubricant/air γ la and lubricant/droplet γ ld interface are found to be 19.7 43 and 39.7 mN m −1 65 . Thus the resulting effective surface tension 37 is 59.4 mN m −1 .…”

“… 50 and utilized in ref. 43 , the LIS was fabricated starting with a single-side polished silicon wafer (100 mm diameter, 525 μm thickness), sputter-coated with a film of aluminum about 100 nm thin. While submerged in low viscosity trimethyl-terminated polydimethylsiloxane (5 cSt, Sigma Aldrich), commonly known as silicone oil, the wafer was heated to 300 ∘ C for 60 min.…”

“…Second, suppressing the coalescence of droplets on LIS is especially challenging, since the oil wetting ridge surrounding the droplets 37 – 39 induces short-range attractive forces that promote coalescence 40 – 42 . Apart from that, in the past few years controlled droplet manipulation on LIS was demonstrated 40 , 43 – 45 , making such systems open droplet microfluidic platforms in their own right.…”

Boosting Electrically Actuated Manipulation of Water Droplets on Lubricated Surfaces through a Corona Discharge

“…29−31 A no-contact electrical stimuli method has been presented as well. 32 However, since the actuation force in this method is based solely on the electrostatic force between the droplet and the electric field applied and needs a large electric field strength, the transporting speed and motion distance are limited. A corona discharge is a self-sustaining atmospheric pressure discharge and is generated when a high electric potential is applied between two asymmetric electrodes.…”