JES Production of Divinylbenzene (DVB) Shells High Average Power Laser Program Workshop Sandia National Laboratory Albuquerque, NM April 9-10, 2003 Jon Streit Diana Schroen

JES Review Progress: –Assembled droplet generator for shell production. –Fabricated approximately 4 mm diameter shells with 300 µm walls at 100 mg/cc. –Overcoated shells with a poly(vinyl phenol) overcoat. –Problems include nonconcentricity, cracking. 4 mm Diameter Foam Shell 300 micron DVB Foam Wall – CH Polymer – ~1-3 Micron Cell Size – mg/cc 1 micron Carbon Overcoat Inner Water Phase Organic Phase Stripping Phase

JES Shell Production Flow Shell production work is occurring in four areas simultaneously with process scale-up in mind: Supercritical Drying Problem: Overcoated shells crack Possible Solution: Slow CO 2 bleed off Formation / Gelation Problem: Shell Nonconcentricity Possible Solution: Density Matching, Agitation Characterization Problem: Difficult Imaging, Cracking, Time Consuming Possible Solution: Index Match, On-site, Automate Overcoating Problem: Time consuming, Need surface characterization Possible Solution: Automate, Perform SEM analysis

JES Agitation Shell deformation during gelation has previously been shown to increase shell concentricity Shell path during gelation has been altered from the original configuration Flask RPM has also been increased to intensify shell deformation Shells have been made to study the effect of agitation, but have not yet been characterized Bottom view of shell path in full flask Bottom view of shell path in 2/3 full flask

JES Density Matching / Initiator The density of the inner water phase and the organic phase change with temperature – this can affect shell nonconcentricity To minimize this effect a low temperature initiator, V-70, was used. Shells made with “pre-polymerization” but at 60°C were tacky and translucent. Shells made without “pre-polymerization” tended to agglomerate. Benefit of V-70 is not apparent. 30°C V-70 65°C AIBN 10 Hour Half-lives V-70 at 50°C should react about as fast as AIBN at 85°C

JES Characterization To increase the rate of data return and to help decrease shell cracking, an on-site characterization technique has been developed. Rinse Away Water with IPA DBP Water DBP IPA DBP/ BSA After Gelation Exchange into BSA BSA Ready to Characterize Two orthogonal images are taken to calculate dimensions Benzyl Salicylate is a better index match making characterization easier and more accurate. DBP = Dibutyl Phthalate, IPA = Isopropyl Alcohol, BSA = Benzyl Salicylate

JES Characterization Equipment Shells are placed in an optical cell and positioned on stage of assembly station to collect images. Effective, but time consuming. Shell images analyzed using Image Pro Plus Software Data exported to Excel.

JES Shell Images: 16% Nonconcentricity Top View Side View Note: Color variation is due to differing lighting conditions.

JES Shell Images: 3% Nonconcentricity Top ViewSide View Note: Color variation is due to differing lighting conditions.

JES Nonconcentricity & Wall Thickness Nonconcentricity % = (4Pi Offset) / (Average Wall Thickness) x 100 4Pi Offset is the greatest distance between the centers of the inner and outer spheres. Example 16% Nonconcentricity: 4Pi OffsetAve. WallNC %Wall Min.Wall Max.Max - Min 42 µm271 µm16 %229 µm314 µm85 µm Example 3% Nonconcentricity: 4Pi OffsetAve. WallNC %Wall Min.Wall Max.Max - Min 9 µm301 µm3 %292 µm311 µm19 µm

JES Rapid Characterization Concept A concept for rapid shell characterization is being developed. Shell that have been exchanged into BSA flow through a tube to an optical cell on the assembly station. Images are analyzed and shells are sorted as Pass or Fail upon exiting the cell. Fail Pass Shells Sorted Optical Cell Shells Flow Through Tube Microscopes (2 Views)

JES Overcoating A few areas need to be studied in the overcoating process: –Does reducing the concentration of the acid chloride slow the reaction and result in an improved surface finish? –A thicker overcoat can be created using a lower molecular with PVP. Would this result in the overcoat growing into the foam? BSA = Benzyl Salicylate, 4CT = 4-Chlorotoluene, ACl = Isophthaloyl Dichloride, PVP = Poly(4-vinyl phenol) BSA Characterized Shell BSA / 4CT 4CT Exchanged into 4CT 4CT/ACl Exchanged into 4CT / ACl 4CT/ACl PVP Placed in PVP Solution (overcoat forms) 4CT/ACl Water Overcoated Shell

JES Overcoating Concept Shells are currently manually overcoated. A concept is being developed to wash shells in a tube and overcoat them as they flow through a coil. = Shell containing Organic Solution of Acid Chloride = Overcoated Shell Water Wash Removes Excess Organic PVP Solution Overcoating Reaction Occurs in Coil Water Rinse 10% HCl Rinse Water Rinse

JES Supercritical Drying We use a semi-automated CO 2 pressure vessel. While supercritical drying of non- overcoated shells has been successful, drying of overcoated shells has been problematic - shells have ruptured. Bleeding off CO 2 over a longer period of time may eliminate the problem. Rupture does demonstrate the seal provided by the overcoat.

JES Future Work Continue to study agitation and density matching as a means to reduce nonconcentricity. Investigate methods to streamline the characterization process. Characterize shells produced in agitation study. Continue to study and streamline the overcoating process and begin to characterize the overcoat. Explore methods to eliminate shell rupture problem during supercritical drying.