Production of Divinylbenzene DVB Shells

1
Production of Divinylbenzene (DVB) Shells

• High Average Power Laser Program Workshop
• Sandia National Laboratory
• Albuquerque, NM
• April 9-10, 2003
• Jon Streit
• Diana Schroen

2
Review

• 4 mm Diameter Foam Shell
• 300 micron DVB Foam Wall
• CH Polymer
• 1-3 Micron Cell Size
• 20 - 120 mg/cc
• 1 micron Carbon Overcoat

• Inner Water Phase
• Organic Phase
• Stripping Phase

• 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.

3
Shell Production Flow

• Shell production work is occurring in four areas
  simultaneously with process scale-up in mind

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

Supercritical Drying

• Problem Overcoated shells crack
• Possible Solution Slow CO2 bleed off

4
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
5
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 60C
  were tacky and translucent.
• Shells made without pre-polymerization tended
  to agglomerate.
• Benefit of V-70 is not apparent.

6
Characterization

• To increase the rate of data return and to help
  decrease shell cracking, an on-site
  characterization technique has been developed.

• 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

7
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.

8
Shell Images 16 Nonconcentricity

• Top View

Side View
Note Color variation is due to differing
lighting conditions.
9
Shell Images 3 Nonconcentricity

• Top View

Side View
Note Color variation is due to differing
lighting conditions.
10
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

• Example 3 Nonconcentricity

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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.

12
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)

13
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
14
Supercritical Drying

• We use a semi-automated CO2 pressure vessel.
• While supercritical drying of non-overcoated
  shells has been successful, drying of overcoated
  shells has been problematic - shells have
  ruptured.
• Bleeding off CO2 over a longer period of time may
  eliminate the problem.
• Rupture does demonstrate the seal provided by the
  overcoat.

15
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.