Robin L. Garrell Department of Chemistry & Biochemistry University of California, Los Angeles

1. HAPL WorkshopOct 2008, Madison, WI Droplet Microfluidics and Target Fabrication: A New Enabling Technology for Inertial Fusion Energy Robin L. Garrell Department of Chemistry & Biochemistry University of California, Los Angeles Jared Hund Inertial Fusion Technology General Atomics, San Diego UC Discovery (IUCRP) Pilot Project for Multidisciplinary Research Oct. 1, 2008 – Sept. 30, 2010. IFT\P2008-089

2. There are a variety of approaches to each part of the capsule fabrication process Formation Centering Coating GDP Stochastic (Rotobeaker) Baseline Techniques Microencapsulation Interfacial Polymerization (hole and seal?) New Techniques Electrowetting DEP Condensed Neon? Other? (acoustic, ect) The current strategy is to refine the baseline techniques while pursuing “out of the box” solutions like electrowetting! Each process step could be mated to others to create the overall process

3. Nozzles used to form double emulsion NEW: Droplet microfluidics • Controlled volume dispensing • Spontaneous double-emulsion formation • Programmed transport Oil 2 Oil 1 R/F droplet device Challenge 2: Obtaining high yield of well-centered particles Hydrogel 70 °C rotate New techniques to address the challenges Challenge 1: controlling size and size distribution Microfluidics and DEP can be automated Scalable (parallel processing) Potentially higher yield of targets that meet spec’s NEW: DEP (Dielectrophoresis): Use external field to center inner droplet before polymerizing.

4. UC Discovery/GA Scope of Work • Advance science and engineering of droplet microfluidics so that a wide range of liquids can be dispensed with accurate and precise control of the volumes (deterministic control of target sizes) • Establish feasibility of using droplet microfluidics to create compound droplets with the dimensions and composition needed for target fabrication • Develop the foam and aerogel chemistries to polymerize the compound droplets into targets. The process will be initiated on the devices, with air or solvent as the ambient medium. • Interface with U of R team to ensure successful integration with active centering technology.

5. 1) Precision dispensing for target fabrication Image from movie demonstrating dispensing of multiple droplets from an on-chip reservoir at lower left. Droplet volumes determine the diameter and wall thickness of the target. Current precision w/o sensing or feedback: 1-5% for water Capacitance sensing with active feedback control will be used to achieve better than ±1% volume precision for water and organic liquids.

6. 2) Creating compound droplets Develop platform and fabricate devices with capacity to: • dispense two immiscible liquids, generally one that is conductive and the other insulating; • actuate the droplets to insert one droplet into the other, creating oil-in-water and water-in-oil compound droplets; • move the compound droplets across the device, in preparation for centering the inner droplet and polymerizing the shell. Target size ranges: • 840-880 µm diameter with 30-60 µm wall thickness • 2.9-3.3 mm diameter droplets with 80-120 µm wall thickness • 4.0-4.6 mm diameter droplets with 170-300 µm wall thickness. Liquid encapsulation: 8 µL dyed water inside 6 µL toluene, sandwiched between Teflon-coated glass plates

7. 3) Fabricating targets Figure 8. Successive images from a movie showing droplet-in-droplet polymerization. In frame 1, the 0.5 µL water droplet at right contains 1 M ammonium persulfate catalyst and 1 M HCl in water. It is actuated toward the 0.5 µL droplet at left, which consists of 1 M aniline in toluene. The water droplet spontaneously inserts into the toluene droplet (frame 2). In frames 3-5 the aniline reacts at the droplet-droplet interface to form a green polymer shell and fibers that penetrate into the inner (water) droplet, as shown in the electron micrograph at right. Under these conditions, polymerization took ~5 min. • Establish feasibility of polymerizaing droplets and shells on-chip • Identify several chemistries that are likely to result in targets with the desired morphology Focus on identifying chemical systems (monomers, initiators, solvents, conditions) •that can be used to fabricate targets and • that are compatible with the liquid dispensing and compound droplet formation methods. Polymerization of polyaniline sphere on-chip

8. Conclusion “Out of the box” techniques (Droplet Microfluidics) are being pursued for capsule fabrication • Amendable to small footprint, automated mass production with low waste UCLA and GA have been awarded a UC Discovery Grant to further this effort • Done with GA internal and UC System funding