Divinylbenzene DVB Shells Foam Buckle Pressure

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

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

• 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.

3
Shell Production Flow

• Shell production work areas

• 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

• Problem Low yield for dried, overcoated shells
• Possible Solution Continue drying /
  overcoating optimization

4
We are Beginning to Work with GA to Develop a
Flow Through System
To Shell Characterization Sort
Droplet Generator
Heated Coil
IPA Rinse
Benzyl Salicylate

• Would agitation be adequate?

Microscopes (2 Views)
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.

New set-up will control stripping temp and
receiving bottle temp until transfer to new
agitator.
Current flask angle and heat source contact area.
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.
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
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
9
Fiber Size
100 mg/cc DVB
TPX Foam
Fiber Size is difficult to Quantify for 100 mg/cc
DVB. The structure resembles that of the string
of pearls structure of an aerogel.
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.

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.
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.
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 Uncoated Shell

• Overcoating polymerization and chemistry
  factors that affect overcoating strength and
  adhesion to the capsule are now being studied to
  increase dry yield.

Dried Overcoated Shell
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.

15
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.