1. JES 4-4-02 1 Initial Production of Divinyl Benzene (DVB) Shells High Average Power Laser Program Workshop General Atomics San Diego, CA April 4 - 5, 2002 Jon Streit Diana Schroen

2. JES 4-4-02 2 Goal Is To Produce Hollow Divinyl Benzene Foam Shells 4 mm Diameter Foam Shell 300 micron DVB Foam Wall CH Polymer ~ 1 micron Cell Size 10 - 100 mg/cm 3 1 micron Polymer Overcoat 0.03 micron Metallic Coating

3. JES 4-4-02 3 Similar Overcoated Foam Targets Have Been Made ILE produced 0.8 mm diameter, 30 micron wall shells from a trimethacrylate foam system. (Takagi, et al) LLNL/Schafer produced 2 mm, 100 micron wall shells from both the trimethacrylate and resorcinol-formaldehyde foam systems. There are two very significant differences in the IFE design –The foam polymer can contain only C and H, no O. –The diameter of the shell is doubled.

4. JES 4-4-02 4 Droplet Generator Droplet generator has been refurbished to accommodate larger spheres, resolve chemical compatibility issues, and increase ease of use. System consists of two syringe pumps, stripping fluid pump, generator assembly, and rotavap. System cost is approximately $8500. System is readily adaptable to making shells with different diameter and wall specifications. Precise control of diameter can be accomplished through wet sieving.

5. JES 4-4-02 5 Flow Rates Determine Diameter And Wall Thickness Target Diameter0.4cmGiven Target Wall Thickness0.03cmGiven Inside Diameter0.34cmTarget Diameter - 2 x Target Wall Thickness Total Volume0.0335mLPi / 6 x (Target Diameter)^3 Inner Water Phase Vol.0.0206mLPi / 6 x (Inside Diameter)^3 Organic Phase Volume0.0129mLTotal Volume - Water Phase Volume Time For Shell Formation1sAdjust stripping fluid rate to form 1 shell per target time period Inner Water Phase Flow Rate 0.0206mL/sInner Water Phase Volume / Time For Shell Formation Organic Phase Flow Rate0.0129mL/sOrganic Phase Volume / Time For Shell Formation

6. JES 4-4-02 6 Formation Of Shells Using Droplet Generator Inner Water Phase: –D 2 O / H 2 O Blend –Syringe Pump –Flows through needle Organic Phase: –Dibutyl Phthalate, DVB, AIBN –Syringe pump –Flows through second orifice Stripping Phase: –5 % PVA in H 2 O –Peristaltic Pump –Flows around second orifice

7. JES 4-4-02 7 Shells Must Gel Quickly To Survive Shells must gel 15 minutes after formation in order to avoid breakage. Temperature, initiators, and adding small amounts of other CH monomers were investigated to reach gelation in this time frame. Gelation is this time frame proved difficult, therefore a “pre- polymerization” step has been added before encapsulation.

8. JES 4-4-02 8 Shell Wall Thickness Data From GA Shell #Ave Wall NC Offset/ Wall Wall Max Wall Min Ave OD Ave ID OD OOR 1 OD ORR 2 70A-128932%381197310125241923 70A-229146%42515731342551838 76A-136021%437283405133313631 76A-238412%430337412433571321 77A-142535%574275408232334844 77A-238016%44231840113252918 Shell OD is close to target. Concentricity requires more work.

9. JES 4-4-02 9 Interfacial Polymerization Produces The Polymer Overcoat INTERNAL WATER PHASE IPA RINSE POLYMER AND ORGANIC PHASE The shell is placed in a reactive aqueous solution. A wall is built at the interface. The shell is placed in organic solvent + acid chloride. WATER PHASE + REACTANT ORGANIC + ACID CHLORIDE LIQUID CO 2 The organic phase and internal water phase must be removed. The shell is rinsed with IPA, then liquid CO 2. The CO 2 is taken supercritical and vented.

10. JES 4-4-02 10 Overcoating Shells After Gelation “Pre-polymerization” Droplet Formation Solvent Exchange Overcoat Solvent Exchange Gelation Dry Advantage: Easier to control overcoating reaction time Disadvantage: More steps (two solvent exchanges)

11. JES 4-4-02 11 Overcoating Shells During Gelation Overcoated beads produced this way Advantages: Reduces shell agglomeration and streamlines production Possible disadvantages: –May alter foam density, composition (Cl or O added), or structure –Water transport “Pre-polymerization” Droplet Formation Overcoat Solvent Exchange Gelation Dry

12. JES 4-4-02 12 Progress To Date Studied gelation rates. Polymerized DVB beads > 4 mm in diameter with densities down to 50 mg/cm 3. Created overcoated polymerized beads in a single step. Polymerized DVB shells ~ 4 mm in diameter at 100 mg/cm 3. Up to 300 shells have been produced per batch. 9 batches sent for characterization. 15 batches produced since overcoming major production obstacles.

13. JES 4-4-02 13 Future Work Produce and characterize overcoated shell. Decide which production method to use. –Overcoating during or after polymerization Need to overcome production problems. –Agglomeration Fine tune density matching to produce high sphericity, uniform wall thickness shells.