How to get SiO2 paticles from ethanol suspension ?

From: Yung-Jen Lin (yjlin_at_ttu.edu.tw)
Date: 10/15/04 

Date: 15 Oct 2004 07:52:18 -0700

I made silica particles from TEOS (tetra-ethyl orthosilicate), which
was dissolved in plenty of ethanol and gelled by adding ammonia water.
The silica particles are spherical with < ~ 0.3 micrometer in diameter
and could suspend in ethanol for a long time. Previously, I was
patient enough to wait for 2-3 weeks to let it settled to the bottom
of the beaker. Then, I syringed away the clear solution in the upper
part and dried the bottom part in an oven to get the solid particles.
Recently, I have a strong feeling that there must be a better way. So,
I try.
Centrifuging is certainly a good way. Unfortunately, the machine is
broken at this moment.
Filtration is also possible. But it is quite slow because the
particles are so small. The filter membrane needs to have small
openings.
Adjusting the pH by adding nitric acid in order to manipulate the
electrical double layer and coagulate. But this seems not woking,
maybe because of the low dielectric constant of ethanol.
The last method occurs to me is to add some kind of polymer or
surfactant. But I do not have any idea of which kind.

Does anyone have similar experience? What is the best way to get those
silica spheres out of ethanol? Thanks.

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