Robin L. GarrellDepartment of Chemistry & Biochemistry

University of California, Los AngelesJared Hund

Inertial Fusion TechnologyGeneral Atomics, San Diego

UC Discovery (IUCRP) Pilot Project for Multidisciplinary Research

Oct. 1, 2008 – Sept. 30, 2010.

Droplet Microfluidics and Target Fabrication:

A New Enabling Technology for Inertial Fusion Energy

HAPL WorkshopOct 2008, Madison, WI

IFT\P2008-089

There are a variety of approaches to each part of the capsule fabrication process

• Each process step could be mated to others to create the overall process

Microencapsulation

Electrowetting

Stochastic (Rotobeaker)

DEP

Baseline Techniques

Other? (acoustic, ect)

Formation Centering Coating

GDP

Interfacial Polymerization (hole and seal?)

The current strategy is to refine the baseline techniques while pursuing “out of the box” solutions

like electrowetting!

Condensed Neon?

New Techniques

New techniques to address the challenges

Oil 2

R/FOil 1

Nozzles used to form double emulsion

Challenge 1: Challenge 1: controlling size and size distribution

rotate

70 °C

Hydrogel

Challenge 2:Challenge 2:Obtaining high yield of well-centered particles

NEW: DEP (Dielectrophoresis):Use external field to center inner droplet before polymerizing.

1. Microfluidics and DEP can be automated

2. Scalable (parallel processing)3. Potentially higher yield of

targets that meet spec’s

NEW: Droplet microfluidics•Controlled volume dispensing•Spontaneous double-emulsion formation•Programmed transport

droplet device

UC Discovery/GA Scope of Work

1) 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)

2) Establish feasibility of using droplet microfluidics to create compound droplets with the dimensions and composition needed for target fabrication

3) 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.

4) Interface with U of R team to ensure successful integration with active centering technology.

1) Precision dispensing for target fabrication

• 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.

Image from movie demonstrating dispensing of multiple droplets from an on-chip reservoir at lower left.

2) Creating compound droplets

Figure 6. 8 L dyedwater inside 6 Ltoluene, sandwichedbetween Teflon-coatedglass plates (surfacesdelineated in red forclarity).

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.

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.

Liquid encapsulation: 8 µL dyed water inside 6 µL toluene, sandwiched between Teflon-coated glass plates

3) Fabricating targets

Polymerization of polyaniline sphere on-chip

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.

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