Divinylbenzene (DVB) Shells Foam Buckle Pressure & Uniformity
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JES 9-24-03 1
Divinylbenzene (DVB) Shells
Foam Buckle Pressure & Uniformity
High Average Power Laser Program Workshop
University of Wisconsin
Madison, WI
September 24-25, 2003
Jon Streit
Diana Schroen
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JES 9-24-03 2
Review
• Status at last review:
– Fabricated approximately 4 mm diameter shells with 300 µm walls at 100 mg/cc and 50 mg/cc.
– Overcoated shells with a poly(vinyl phenol) overcoat.
– Developed in-house characterization method.
– All overcoated shell cracked during drying process.
– No characterization of overcoat.
• 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
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JES 9-24-03 3
Shell Production Flow
• Shell production work areas:
• Problem: Low yield for dried, overcoated shells• Possible Solution: Continue drying / overcoating optimization
• Problem: Shell Nonconcentricity
• Possible Solution: Design / Obtain new apparatus for gelation with improved temperature and agitation control.
• Problem: Time Consuming• Possible Solution: Automate
• Problem: Time consuming, Poor initial surface finish• Possible Solution: Automate, Optimize chemistry, reaction conditions
Supercritical Drying
Formation / Gelation
Characterization
Overcoating
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JES 9-24-03 4
We are Beginning to Work with GA to Develop a Flow Through System
Droplet Generator Heated Coil IPA Rinse
Benzyl Salicylate
To Shell Characterization
Sort
Microscopes (2 Views)
Shells Sorted
Fail
Pass
Optical Cell
Shells Flow Through
Tube
• Would agitation be adequate?
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JES 9-24-03 5
Agitation & Temp During Gelation
• Shell characterization data relating non-concentricity and density matching has been scattered.
• Current generator set-up has poor temperature control and non-uniform agitation.
• To remedy this, a new generator set-up and two new agitation methods have been devised.
Current flask angle and heat source contact area.
New set-up will control stripping temp and receiving bottle temp until transfer to new agitator.
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JES 9-24-03 6
Gelation Equipment
A hybridization oven has been ordered to gel shells using a carousel motion. The angle the tube is held in the carousel can also be adjusted to
provide a sloshing motion for periodic deformation of the shell.
A bottle rotator that is submersible in a heated bath is
being designed for superior heat transfer and uniform agitation.
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JES 9-24-03 7
Benzyl Ether as Dibutyl Phthalate Replacement
• Benzyl ether was tested as a dibutyl phthalate substitute to allow gelation and characterization in the same solvent.
• Same density and similar solubility parameters as DBP.
• Index of refraction is higher (1.56 vs. 1.49)
Shell Gelled using DBP in Water
Shell Gelled using BE in Water
Shell Gelled using BE in BE
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JES 9-24-03 8
Cell Size
100 mg/cc DVB Polymerized using Dibutyl Phthalate as the Solvent.
100 mg/cc DVB Polymerized Using Benzyl Ether as a Solvent.
Cell Size is Larger Using Benzyl Ether
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JES 9-24-03 9
Fiber Size
100 mg/cc DVB
Fiber Size is difficult to Quantify for 100 mg/cc DVB. The structure resembles that of the “string of pearls”
structure of an aerogel.
TPX Foam
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JES 9-24-03 10
Overcoating
• Overcoating experiments have begun.
• Surface roughness is greater then seen in previous work.
• We are varying reaction time, pH, reactant concentration, PVP molecular weight, crosslinker, and crosslinker concentration to try to reduce the surface roughness.
• SEM photos of initial overcoat have been taken.
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JES 9-24-03 11
Overcoat SEM Images
5000x, 20K PVP, 5 min 25000x, 20K PVP, 5 min
At 5 minutes, the overcoat does not look complete and appears rough.
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JES 9-24-03 12
Overcoat SEM Images
5000x, 20K PVP, 15 min 25000x, 20K PVP, 15 min
At 15 min, the overcoat shows some improvement, but still rough.
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JES 9-24-03 13
Supercritical Drying
• Yields from drying shells are still low – at best 30%.
• Initially we thought that slowing the rate of CO2 bleed off would increase yields – but this seems to have little effect.
Dried Overcoated Shell
Dried Uncoated Shell
• Overcoating polymerization and chemistry factors that affect overcoating strength and adhesion to the capsule are now being studied to increase dry yield.
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JES 9-24-03 14
Buckle Pressure
Hole in Foam Overcoat Failure Crack in Foam
• Shells do not dimple as expected. Failure modes are through gross foam failure, overcoat delamination, or cracks in the foam.
• Permeation is rapid for the initial overcoats – shells do not yield if pressure is increased at a moderate rate.
Buckle Pressure
0
10
20
30
40
50
60
70
80
20 40 50 60 80 100 200Pressure (psi)
Bu
ckl
e P
erc
ent
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Future Work
• Study nonconcentricity results for new droplet generator / agitator set-up with relation to density matching.
• Continue to study and streamline the overcoating process and study the effects of overcoating chemistry and reaction conditions on overcoat surface roughness.
• Explore methods to eliminate shell rupture problem during supercritical drying including overcoating chemistry and reaction condition effects.
• Continue generating buckle pressure data.