Re: Question: water-soluble thickeners
- From: Uncle Al <UncleAl0@xxxxxxxxxxxxx>
- Date: Wed, 30 Mar 2005 07:49:38 -0800
aupward wrote:
>
> Thanks everyone for the insightful responses! What a neat group.
>
> A bit more info:
> - To be practical, let's say the block is a square meter (as large as
> possible), that means ~ 1000 L
> - The block just has to hold its shape, doesn't need to be super-rigid
> - Some light scattering is acceptable, with minimal color shift
> desirable
>
> The most important factors driving the choice of thickener will be:
> - Cost, and availability in quantity
> - Ease of handling/processing - easy to mix and store the block at
> room temp
>
> If anyone has any other suggestions with regards to the above, they
> would be graciously received.
Do the obvious: Get a meter+ of plastic irrigation pipe with ID
sufficient to look down. Cast meter thicknesses of candidate gels and
see if they are transparent down their length. You will be
disappointed.
Whoa! Storage? If it is based in water it will evaporate at the
surface.
A cubic meter is a metric tonne of water. Casting a perfect cubic
meter net of acrylic will set you back approaching seven figures.
Degassed Pt-cure silicone might pull it off in the doing but the price
for material is high, ~$(US)30-50/lb. I don't know any gel that will
tolerate that kind of unsupported tensile stress at its base without
rupturing.
Making a clear cubic meter of anything has multiple problems,
1) Heat. Cooling a molten or exothermic setup will take weeks or
months. There is no convective cooling. You will get thermal
runaways with polymerization.
2) Contraction. As the temp drops the stiff shrinks. If the
surface is rigid you get negative pressures inside leading to material
rupture. If it is a chemical cure (silicone), monomer to polymer
shrinks. If it is a chemical cure and it exotherms, it runs away at
the pseudoadiabatic center as the temp climbs. Negative pressure
causes refractive index excursions.
3) Bubbles. Degassing a tonne of liquid takes some doing, even if
you bubble helium through it.
4) Bottom rupture in tension. The weight of overlying stuff makes
the base want to spread. Gels and brittle materials are not strong in
tension. Gels deform and make things worse.
I suppose a cubic meter of clear Kraton thermoplastic elastomer is
doable. It will suffer a lot of light scattering at a meter
thickness. You can gel a reasonably clear cubic meter of water with
agarose, but I doubt it will hold together under its own weight. A
kid comes along, punches it, the surface splits...
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
- Prev by Date: Re: Question: water-soluble thickeners
- Next by Date: Re: Polystyrene + alkanes = ?
- Previous by thread: Re: Question: water-soluble thickeners
- Next by thread: re:Question: water-soluble thickeners
- Index(es):
Relevant Pages
|
