Production of Divinylbenzene (DVB) Shells

1
Production of Divinylbenzene (DVB) Shells

• High Average Power Laser Program Workshop
• Naval Research Laboratory
• Washington, DC
• December 5, 2002
• Jon Streit
• Diana Schroen

2
Review

• 4 mm Diameter Foam Shell
• 300 micron DVB Foam Wall
• CH Polymer
• 1 micron Cell Size
• 20 - 100 mg/cc
• 1 micron Carbon Overcoat
• 0.03 micron Metallic Coating

• Refurbished droplet generator to accommodate
  larger shells
• Polymerized DVB shells 4 mm in diameter at 100
  mg/cc
• Obtained characterization data for first six
  batches of shells
• Concentricity primary problem
• Created gelled, overcoated beads in a single step

3
Density, Interfacial Tension, and Agitation

• Work has focused on density matching.
• Density matching helps center the inner and outer
  drop, but density is a function of temperature.
  If the inner water core of the shell has the same
  density at room temperature as the surrounding
  organic layer, the densities will not be the same
  at the elevated gelling temperature because the
  thermal expansion is not the same for the
  different solutions.
• Influences of interfacial tension and agitation
  need to be studied further as will be seen.
• M. Takagi, R. Cook, R. Stephens, J. Gibson, S.
  Paguio, Decreasing Out-Of-Round in Poly(a-Methyl
  Styrene) Mandrels by Increasing Interfacial
  Tension, Fusion Technology, Vol. 38, p. 46 July
  2000.
• T. Norimatsu, Y. Izawa, K. Mima, P. M. Gresho,
  Modeling of the Centering Force in a Compound
  Emulsion to Make Uniform Plastic Shells for Laser
  Fusion Targets, Fusion Technology, Vol. 35, p.
  146, March 1999.

4
Initial Density Matching Results in 5 PVA

• Chart represents the calculated room temperature
  density difference between the inner water core
  and the organic phase compared with the average
  measured nonconcentricity percent.
• Initial results indicated that the optimal
  density difference would occur at about 0.012
  g/cc.
• Shell characterization provided by GA.

5
Additional Density Matching Results in 5 PVA

• After more data was collected in the 0.010 to
  0.012 g/cc range, the trend appeared to be less
  clear. Optimum appeared to be about 0.019 g/cc.
• A V shape would be expected when the data is
  plotted in this manner.

6
Reinterpreted Density Matching Data in 5 PVA

• Examining the results for a greater than 0.015
  g/cc density difference should help clarify the
  situation.
• Other factors to reduce nonconcentricity are
  being investigated (temperature, interfacial
  tension, agitation).

7
Initial 0.05 PAA Density Matching Results

• PAA has been investigated as a replacement for
  PVA. PAA has been shown to increase interfacial
  tension leading to decreased out-of-round in the
  PAMS shell system.
• Initial results in PAA suggest that density
  matching may not be the determining
  nonconcentricity factor.

8
Temperature Dependence of Density

• Temperature in gelation flask was found to vary
  from 65-73 ?C. This causes a fluctuation in the
  density match.
• A temperature controller
• was obtained to
• minimize temperature
• fluctuations.
• DVB polymerization
• experiments using UV
• initiation performed.
• Polymerization achieved,
• but presently too slow to
• be useful.

9
Agitation

• A cylindrical flask has replaced a pear shaped
  flask more uniform agitation.
• Centering forces have been shown to be generated
  with shell deformation.
• Shells travel in an undisturbed circular pattern
  when the flask is completely full of solution.
• Filling the flask with less solution adds
  disruption to shell path.

Bottom view of shell path in full flask
Bottom view of shell path in 2/3 full flask
10
Shell Overcoating Has Begun
The organic phase and internal water phase must
be removed.
The shell is placed in organic solvent
acid chloride.
ORGANIC ACID CHLORIDE
The shell is rinsed with IPA, then liquid CO2.
The CO2 is taken supercritical and vented.
The shell is placed in a reactive aqueous
solution. A wall is built at the interface.
11
Overcoating Characterization
Uncoated Shell
Coated Shell

• Confocal image of shell.
• 900X magnification.
• Image is 100 microns across.
• All features are submicron in depth.

12
Shell Cracking

• Shells do not ship well - 25 broken or cracked
  after shipment.
• 95 broken or cracked after exchanging to DBP
  for characterization (estimates and image from
  GA). Handling needs to be minimized.
• Cracking less problematic when exchanging into
  IPA needs to be monitored.

13
Radiographic Characterization

• X-ray radiograph of shell.
• System is being modified for foam needs
  optimizing energy and adding rotation.
• System currently has 28 micron resolution.
• Also designing tomographic system with 10 micron
  resolution planned for FY04.

14
Future Work

• Determine optimal density matching and its
  significance.
• Determine advantage of using PVA or PAA system.
• Examine influence of agitation.
• Determine methods to reduce shell cracking.
• Develop x-ray radiography characterization
  system.
• Develop wet characterization system at Sandia.