Many thanks for the suggestions. We'll check them.
We thought about using spin coating, but our solution is extremely
non-viscous, so we think it wouldn't help so much.
Dept. Analytical and Organic Chemistry
University Rovira i Virgili of Tarragona
Catalonia - Spain
First you need to disperse your particles better. With metal
nanoparticles, using aqueous solutions is very difficult even with
some of the best ammonium polymethacyrlate type dispersants or
electrostatic methods. Your organic solvents should work well though.
If you want to stick with methanol try some of the traditional powder
processing dispersants (ie menhaden fish oil or hypermer KD1 (made by
ICI surfactants)). You should only need less than a weight % to make
a significant improvement. Disolve your dispersant (polymer) in
solution, add your nanoparticles and disperse with an ultrasonic
probe. I have had good success dispersing carbon nanotubes in
toluene, etoh, and MEK with the fish oil in this manner. Remember if
you have good dispersion, you will not be able to see particles or
colloids with the eye. The solubility of the fish oil is improved
with about 20-40%xylene in meoh or etoh allowing the polymer chains to
stretch out and improve the steric barrier.
To thicken your solution for spin casting add some ethyl cellulose
(49% + ethoxyl content) until desired consistency is achieved
(approximately 10wieght% yields the viscosity of maple syrup).
Polyvinylbutyral works well too, but you might need a bit more to
reach equivalent viscosity of the ethyl cellulose. Further, if
absolutely clean burnout is required, use polypropylene carbonate
(trade name QPAC-40), this is the absolutely cleanest binder for
burnout which decomposes in air, vacuum, or inert. Of course you will
need to work with acetone or MEK solutions for decent solubility which
should also disperse your particles with the fish oil.
Yet one more final option is too use a higher viscosity solvent.
Alpha terineol is wonderful with a little oleic acid for the
dispersant. The alpha terpineol dries very slow, but levels
beautifully, and is quite non-toxic compared to other solvents. If
you need more body for spin coating, a % or so of ethyl cellulose will
do the trick.
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