divinylbenzene (dvb) shells
DESCRIPTION
Divinylbenzene (DVB) Shells. High Average Power Laser Program Workshop Princeton Plasma Physics Laboratory Princeton, NJ October 27 th -28th, 2004 Jon Streit, Diana Schroen Schafer Corporation Reny Paguio, Brian Vermillion General Atomics. Review. 4 mm Diameter Foam Shell. - PowerPoint PPT PresentationTRANSCRIPT
JES 10-27-04 1
Divinylbenzene (DVB) Shells
High Average Power Laser Program Workshop
Princeton Plasma Physics Laboratory
Princeton, NJ
October 27th-28th, 2004
Jon Streit, Diana Schroen
Schafer Corporation
Reny Paguio, Brian Vermillion
General Atomics
JES 10-27-04 2
Review
• Status at last review:
– Lowest average batch NC was 4 %. Further improvement needed.
– Smoothness of PVP overcoat improved, shrinkage still problematic.
– Investigation of alternatives to PVP initiated.
• 300 micron DVB Foam Wall– CH Polymer– ~1-3 Micron Cell Size– 20 - 120 mg/cc
• 1-5 micron Carbon Overcoat
• Shell formed through microencapsulation
• Overcoat applied with interfacial polycondensation
4 mm Diameter Foam Shell
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Shell Production Status
Formation / Gelation
We have switched to a horizontal flask configuration which has lowered average batch nonconcentricity to 3%. Individual shells have been characterized with NC <2%. 3% NC can be achieved with GA’s dual initiator method at 30 °C or with a single initiator at 80 °C. The combination of the different shell flow pattern and a longer gelation time (>1 hr) has lowered NC.
Overcoat
To try to reduce shrinkage of the PVP overcoat, PVP has been combined with small amounts to up to 50% of two different tri-functional monomers. Diethylenetriamine and melamine formaldehyde have been investigated as possible PVP alternatives.
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Nonconcentricity and Density Matching
Density matching appears to have an effect with a horizontal flask at 75 °C to 80 °C, lowering NC about 2%. It does not seem to have an effect with
the two initiator system at 30 °C.
No Density Matching Density Matched
Batch Temperature NC% Batch Temperature NC%
80C 80 5 81A 80 3
81C 80 5 80A 75 3
79A 75 6 96A 80 3
79B 80 6 95A 80 4
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Accuracy of Density Matching Increased
Liquid Level
Average Temperature Calculated for Area
Oil Bath
To increase the accuracy of density matching, an IR camera is being used to more accurately determine the temperature in the flask. The temperature in the flask has been found to be lower than previously thought, which has resulted in adjustments being made to increase DM accuracy.
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Nonconcentricity and Agitation
Three different flask configurations have been used with very different results.
Flask Configuration
Full, Angled 2/3 Full, Angled1/2 Full,
Horizontal
NC % (Four Best batches)
15 4 3
21 5 3
41 5 3
46 6 4
Flow Patterns
Bottom ViewHorizontal, Side
View
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Flask Dimensions
Flask Dimensions (Diameter x
Length)
Side View of Flask
Lowest NC%
60 x 100 mm 6
100 x 100 mm (standard)
3
125 x 50 mm 5
125 x 100 mm 4
• Since flask fill level and orientation appears to have a dramatic effect on NC, the effect of flask dimensions on NC is being examined.
• Flow patterns are different for each flask – the frequency and degree of deformation may affect NC.
• Initial results have not shown a dramatic effect on NC.
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PVP Shrinkage
Smoothest PVP/5%DET Coating (RMS surface roughness = 25 nm)
• To reduce PVP shrinkage several methods have been tried:
- PVP with low concentration of trifunctional monomers
- PVP with 50% trifunctional monomers
- Flash trifunctional coatings followed by PVP coatings
- Flash PVP coatings followed by trifunctional coatings
• PVP shrinkage occurred in all of the above methods. Surface finish tends to be good despite shrinkage.
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Melamine Formaldehyde Coating Process
1. Gelled Shell 2. Place Shell in MF Solution
at 70 °C
3. Shell is then exchanged to IPA & CO2
Dried
• Melamine formaldehyde was selected for investigation because of its straightforward processing conditions and reports of its smoothness
• An aqueous solution of melamine and formaldehyde at elevated pH is heated to produce a precondensate
• A gelled shell is placed in the precondensate solution and the pH is lowered – MF polymer then condenses on the organic surface
Finished
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PVP / MF Surface Comparison
5000x, 20K PVP, 5 min 5000x, highly crosslinked MF, 1 Hour
The MF has a generally smooth appearance with clusters of excess polymer attached. Can the excess polymer be removed through washing or prevented?
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MF Drawbacks
0.5
Two problems have been encountered with the MF coating:
• Coating thickness is thin – about 0.5 microns. Can thickness be increased?
• Micro cracks can occur during the drying process. Could these be eliminated with a thicker coating?
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Melamine Formaldehyde Surface Finish
Interferometer surface roughness measurement of a 60 x 46 micron area of Melamine Formaldehyde. Surface roughness is 32 nm RMS.
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Future Work
• Continue to reduce nonconcentricity through careful control of temperature, density matching, agitation and gelation time.
• Continue experimentation with additives to try to reduce PVP shrinkage.
• Continue to investigate overcoat layering and PVP alternatives.
• Attempt to increase thickness of melamine formaldehyde coating to eliminate micro-cracks.