Initial Production of Divinyl

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• 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

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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/cm3
• 1 micron Polymer Overcoat
• 0.03 micron Metallic Coating

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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.

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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.

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Flow Rates Determine Diameter And Wall Thickness
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Formation Of Shells Using Droplet Generator

• Inner Water Phase
• D2O / H2O Blend
• Syringe Pump
• Flows through needle
• Organic Phase
• Dibutyl Phthalate, DVB, AIBN
• Syringe pump
• Flows through second orifice
• Stripping Phase
• 5 PVA in H2O
• Peristaltic Pump
• Flows around second orifice

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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.

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Shell Wall Thickness Data From GA

• Shell OD is close to target.
• Concentricity requires more work.

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Interfacial Polymerization Produces The Polymer
Overcoat
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.
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Overcoating Shells After Gelation
Pre-polymerization
Droplet Formation
Gelation
Solvent Exchange
Overcoat
Solvent Exchange
Dry

• Advantage Easier to control overcoating
  reaction time
• Disadvantage More steps (two solvent exchanges)

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Overcoating Shells During Gelation
Pre-polymerization
Droplet Formation
Overcoat
Solvent Exchange
Gelation
Dry

• 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

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Progress To Date

• Studied gelation rates.
• Polymerized DVB beads gt 4 mm in diameter with
  densities down to 50 mg/cm3.
• Created overcoated polymerized
• beads in a single step.
• Polymerized DVB shells 4 mm
• in diameter at 100 mg/cm3.
• Up to 300 shells have been
• produced per batch.
• 9 batches sent for characterization.
• 15 batches produced since overcoming major
  production obstacles.

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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.