Selected TOPpaper 2007 in Journal of Physics Condensed Matter

Electrowetting-controlled droplet generation in a microfluidic flow-focusing device

Florent Malloggi, Siva A. Vanapalli, Hao Gu, Dirk van den Ende and Frieder Mugele

J.Phys.: Condens.Matter 19 (2007) 462101 (7pp)

Frieder Mugele and collegues from the University of Twente report improvements in conventional electrowetting.

Droplet-based microfluidic research has potential applications in biochemical reactions, material synthesis, single-cell analysis and novel fluid logical devices. Commonly pressure-driven flows are used to create droplets continuously, providing high throughput capability, but it cannot generate individual drops on demand nor provide dynamic control of surface wettability, which can dramatically affect the dynamics of two-phase microflows. Alternatively, the EW-on-dielectric approach is used to digitally manipulate drops, providing exquisite control over individual drops and surface wettability, but with low throughput and it cannot readily be integrated with existing channel-based technologies.

Mugele et al adopt a unified approach to create a soft microfluidic platform combining the advantages of both methods. They incorporate EW into a flow-focusing device and demonstrate EW-controlled drop formation. They identify experimentally the range of voltages and driving pressures that yields EW-induced droplet generation. A theoretical description based on the balance of external pressures and voltage-controlled capillary pressures quantitatively accounts for the observations. They show that with this unification the smaller the geometric scales the more efficient the EW control of drop generation