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

Target fabrication is a major bottleneck in the development of inertial confinement fusion as an energy source. Current bulk processing methods for laser target fabrication suffer from low yield. This thesis reports experimental results on the application of microfluidics to form double emulsion (DE) droplets used for fabrication of cryogenic foam targets. This microfluidic assembly-line automates the production process to achieve droplet-by-droplet processing so that each DE droplet meets the specifications. Because it is electrically controlled, this scheme provides excellent flexibility and scalability.;The voltage controllable electrowetting-on-dielectric (EWOD) and dielectrophoresis (DEP) effects make it possible to manipulate both conductive and dielectric droplets simultaneously on a microfluidic chip. We present a simple model to calculate the electric actuation forces using lumped parameter electromechanics. This model, identifying the frequency-dependent relationship between EWOD and DEP, can be used to predict the operational conditions to actuate particular liquids.;We demonstrate that aqueous and nonaqueous liquid droplets can be dispensed from on-chip reservoirs by EWOD and DEP actuations, respectively. Dispensed droplet volume reproducibility is tested over a range of operational parameters, including applied voltage, cutting electrode length, and the effect of connecting traces. By optimizing the operating conditions, we obtain a reproducibility of ±3.0%, which is adequate for the laser target fabrication according to our sensitivity analysis.;DEP based manipulation of oil usually requires much higher voltages than water actuation. We introduce a new method of actuating oil droplets in water medium that exploits negative DEP to reduce oil actuation voltages. Theoretical modeling and experimental demonstrations for this scheme are presented. Microfluidic operations of transporting, splitting, merging, and dispensing of oil droplets are achieved at a voltage level of ∼100 V.;After dispensing water and oil droplets, these droplets have to be combined to form DE droplets. We develop a Gibbs free energy model to test the likelihood of DE formation and present experimental results showing the formation of both water-in-oil and oil-in-water DE droplets in parallel-plate structure. In addition, we also investigate the form of DE droplets in open structures. The requirements to eject a droplet from a closed section are determined by force analysis. Corresponding experimental tests are done to demonstrate droplet movements from closed to an open section. While the ejection of water droplet is easily achieved by EWOD actuation, an oleophobic surface must be used to eject an oil droplet. We investigated two types of oleophobic surfaces- electrospun fiber mats and re-entrant Si structures, and used the latter one to achieve oil ejection movement.