1. Schafer Corporation An Employee-Owned Small Business Schafer Laboratories Schafer Corporation at Sandia National Laboratory 1515 Eubank SE, M.S 1196 Albuquerque, NM 87123 505 845-7762 (tel.) 505 845-7820 (fax) dgschro@sandia.gov Advanced Foam Shell Production Laser IFE Program Workshop Diana Schroen-Carey Naval Research Laboratory February 6-7, 2001

2. DSC 2/5/01 2 Target Fabrication-3: Foam shells----Schafer Corp Overall Objective………….Develop DVB Foam Shells for targets FY 01 Deliverables………..1. Develop method to microencapsulate Divinyl Benzene (DVB) foam 2. Make DVB shells 3. Make proof of principal overcoated shells (interfacial polymerization) PI Experience………………. Identified DVB as promising. Foam expert. Proposed Amount………….. $ 150 k (POC: D. Schroen-Carey) Relevance of Deliverables [X] NIF……………………Needed for direct drive targets for the NIF [ ] Laser RR Facility…. [X] Other DP/NNSA……SNL wants to make extensive use of DVB foam [X] Energy………………DVB has promise to meet DD target plus mass production requirements. Related OFES activities……Only foam work is for HIB at LANL

3. DSC 2/5/01 3 The Baseline Target Requires a Novel Polymer Foam Shell. 1500 micron vapor center 190 micron fuel layer 289 micron foam filled with fuel 1 micron carbon overcoat.03 micron gold coating 4 mm foam shell 289 micron CH foam wall 1 micron carbon overcoat.03 micron gold coating

4. DSC 2/5/01 4 Similar Overcoated Foam Targets Have Been Made. ILE produced 0.8 mm diameter, 30 micron wall shells from a trimethacrylate foam system. 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 size of the shell is doubled.

5. DSC 2/5/01 5 We Are Developing a New CH Foam. Divinyl benzene (C 10 H 10 ) can be used to make foams in the density range of 10 - 250 mg/cm 3. The process is an extension of processes used by Steve Letts (LLNL) and Warren Steckle (LANL) At 10 mg/cm 3 the average cell size appears to be about 1.6 microns. The monomer is available fully deuterated (LANL). We are studying methods to increase the cross linking and to reduce the cell size. This SEM shows the cell size and morphology of a 10 mg/cm 3 foam. This photograph shows a 14 mg/cm 3 foam in isopropanol. It was cast with tabs at each end.

6. DSC 2/5/01 6 We Will Produce Foam Spheres Using A Droplet Generator. The versatility of the droplet generator is shown by its ability to make both trimethacrylate (oil soluble) and RF (water soluble). All three phases are driven by separate pumps. This allows the wall thickness and diameter to be independent. Drawing by S. Buckley

7. DSC 2/5/01 7 There Are Two Issues That Will Have To Be Addressed. The W/O droplet must gel within about 15 minutes to prevent damage. The typical DVB polymerization is 24 to 48 hours. This problem was also encountered with the RF system. –Begin the polymerization prior to droplet formation. By doing viscosity vs. time studies we can determine the last possible opportunity to microencapsulate. –Add a small molecule cross linker. –Add a more reactive polymerization initiator. The surfactant system must be optimized. The surfactants stabilize the interfaces and the exterior water phase surfactant (protective colloid) effects agglomeration and sphericity.

8. DSC 2/5/01 8 DVB Beads Have Been Made. Beads were very high density - 250 mg/cm 3 and produced by “shake and toss” technique so there was no diameter control. Hollow spheres were tried at 40 mg/cm 3, no spheres survived. – gelation studies – rotary flask Agglomeration was a slight problem, but the system appears to be quite similar to the trimethacrylate system. Ruler divisions are 1 mm.

9. DSC 2/5/01 9 After Polymerization, the Spheres Will Be Solvent Exchanged and Overcoated. 1. Wash out internal water phase by several solvent exchanges. 2. Exchange into solvent with an acid chloride reactant. 3. Transfer into a water phase with a hydroxyl reactant. A polymer wall forms just at the interface. 4. Repeat solvent exchanges, exchange into CO 2, and dry by taking it supercritical. R 1 -Cl 1 2 R 2 -OH R 1 -R 2 3 4

10. DSC 2/5/01 10 There Are Many Candidates For The Polymer Overcoat. Final Report 96CR/LL2 “Foam Shell Development and Production: Overcoating Process” The desired wall thickness and surface finish will limit the candidates - higher functionality should meet requirements. Isopropanol washing should improve on the reported surface finish.

11. DSC 2/5/01 11 We Anticipate Making Foam Spheres and Prototypes Of Overcoated Spheres This Fiscal Year. Need to purchase pumps and interfacial polymerization chemicals. Gelation (viscosity studies) can begin immediately. Deliverables will be: –microencapsulated DVB spheres, diameter and wall thickness will approximate current design. Sphericity and wall uniformity will still need to be optimized. –prototypes of overcoated spheres.