Surfactants are designed to suspend hydrophobic materials into water
solutions. I am not sure that any would work well to suspend a hydrophilic
particle into an oil. Usually soaps have an organic tail with a short
hydrophilic end.

Also, I am not sure that the surfactant would disperse in a non-aqueous
solution.

The basic problem is that TiO2 is polar and you wish to disperse them into
non-polar liquids. This material is very finely divided and has a high
surface area and hence a very high work function for dispersal into a
non-polar liquid. Also, the particles in contact with each other would have
a lower work function.

You need to treat the TiO2 powder such that it has a hydrophobic non-polar
surface. Perhaps some carboxylic acid or such so the organic molecule is
bound to the surface with its organic tail facing outward. Or mix the TiO2
powder in water with the surfactant and then dry it.

Another approach might be to disperse the TiO2 in water and then mix the
water with acetone or ethanol. The composition won't be 100% acetone or
ethanol though.

Finally, some shearing mixing might be of use than just relying on
Ultrasonic mixing.

Ed



-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of oygm
Sent: Thursday, November 19, 2009 3:45 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Dispersion of TiO2 nanopowders in oil


Hello everyone,

I am facing the problem that I can not disperse the TiO2 nanopowders(<25nm)
evenly into the silicone oil.

I have tried to mix TiO2 nanopowders with different solutions and find out
that they are dispersed well in water but have some problems with other
solutions like acetone, ethanol, silicone oil. Ultrasonic is used during
mixing for 2 hours, the result is that the TiO2 nanopowders is aggregated
and separated with the solution. I have also tried surfactant like
PEG(0.5-1wt%), then part of the powders is dispersed into oil but not all of
them. The aggregation of nanopowders is still visible.

Does anybody have some experience about how to disperse TiO2 nanopowders in
oil?  Any other kinds of surfactant I should try?

Advice and suggestions are highly appreciated. Thanks.

Regards,

G.M. Ouyang
Ph.D student
Vestfold University College
Norway