Digital Microfluidics: Electrowetting Droplet Actuator (2D)

Digital Microfluidic Chip (2D top-down)

Select a droplet, then click an electrode

Electrode saturation voltage 30 V

Coating hydrophobicity (rest angle) 152°

Action mode

Live readout

Selected droplet

–

Droplets on chip

Rest contact angle θ₀

–

Active contact angle θ(V)

–

Steps moved

Splits / Merges

0 / 0

How it works

A droplet sits on a hydrophobic dielectric coating over a grid of electrodes with no applied field, beading up at a high rest angle θ₀ (drawn here as a small top-down footprint circle). Grounding the droplet and biasing one electrode creates an electric field across the thin dielectric that locally lowers the effective solid-liquid interfacial energy — the Young–Lippmann equation:

cos θ(V) = cos θ₀ + (ε₀ε_r)/(2γd) · V²

θ(V) drops toward that electrode, growing the footprint radius there and pulling the whole droplet one cell over — repeat on neighboring electrodes to walk it anywhere on the grid.
Split activates electrodes on both sides at once: the footprint stretches into an ellipse, the neck thins, and surface tension pinches it into two independent droplets.
Merge brings two droplets onto adjacent electrodes until their footprints touch and coalesce into one, volumes summing (r³ adds, since surface tension conserves total liquid volume).

Real EWOD (electrowetting-on-dielectric) devices saturate around 60–70° regardless of how much higher the voltage climbs — the model below caps θ(V) at that floor, just like the physical effect. A smaller θ means a wider, flatter contact-line footprint, which this top-down view draws directly as a larger circle/ellipse.

Droplet (liquid, top-down) Electrode — voltage ON Electrode — voltage OFF

Click a droplet to select it, then click a neighboring electrode pad to move / split / merge.