On-Chip Double Emulsion Droplet Assembly Using Electrowetting-on-Dielectric and Dielectrophoresis

The double emulsion (DE) droplets used for fabrication of cryogenic foam targets for inertial confinement fusion experiments require precisely controlled volumes. On-chip electric field actuated microfluidic assembly of DE droplets can be used to achieve such precision. The electrowetting-on-dielectric and dielectrophoresis effects make it possible to manipulate both conductive and dielectric droplets simultaneously on a substrate. Aqueous and nonaqueous liquid droplets precisely dispensed from two reservoirs on a microfluidic chip are transported and combined to form oil-in-water-in-air or water-in-oil-in-air DE droplets. The dispensing reproducibility is studied as a function of a set of operation parameters. Conditions for spontaneous emulsification for DE formation are developed in terms of droplet surface energies.