Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: dylanail on October 01, 2015, 04:44:54 PM
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Hi, I am looking for an instantly evaporating solvent that PVOH is soluble in. It is for a project that involves shooting it out of a vessel with CO2 so it dries instantly, or near-instantly (±1.5 seconds) Thanks! ;D
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Hi,
the evaporation times relates with the size more than with the solvent (methanol?). Heat helps too.
If you achieve to evaporate the solvent so quickly, expect a porous solid.
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I need it in the form of a thin, rope-like strand. There is an extruder with 8 holes that will touch a block to adhere the material to it, and then spin rapidly while moving farther away to sort of weave it into a cord. Maybe a gel?
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Also, it will be shot out using compressed CO2.
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If the strands can be very thin, maybe - there is not limit in this direction. Methanol is volatile and heat helps. But I expect a porous polymer then.
One standard method would be instead to extrude the hot polymer. Enough pressure lets it flow even though it's far from molten, so under its own weight it deforms little enough. Just like injected plastic parts are ejected immediately from the mold without cooling first.
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Ok. The formula keeps changing with this. There will also be Graphene Oxide in the polymer. I have done research and read that only 1.8% Graphene Oxide increases the tensile strength 150%. This will have to be as strong as possible. I was also thinking of using maybe Magnesium Oxide to help it expand more. Also, the CO2 is necessary because it may have to spray across small distances. Also, I was thinking of using 3 ball bearings confined in a tube, with the liquid shot out of that because it will be smoother, reduce jams, and give lots of small crevices for the liquid to extrude from, variating the stream size.
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Are you trying to make Spidey rope (as in Spiderman)?
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Hah, I wish... :) Nope, It's for a school chemistry project.
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Is using PVOH an absolute requirement? It has very few effective solvents. The hydrogen bonding is much too strong and so effective solvents end up needing strong hydrogen bonding as well. Not much is likely to work besides water and ionic liquids neither of which are suitable. Methanol is perhaps the best bet but not if it takes a large amount of solvent to dissolve a small amount of PVOH.
How about just a partially hydrolyzed PVAc? PVAc boasts many more solvents and there is a continuum of polymers between it and PVOH.
How much of it has to evaporate in '±' 1.5 seconds? Does it just need strength to hold its own weight or does it need to be entirely gone? Do you get extra credit if it all evaporates within minus 1.5s of instantly? ;D
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I definitely considered the PVAc, but it was too weak. The strength of PVOH is what I need in this case. And partially hydrolyzed PVOH would probably be a good idea.
Sorry, I don't know why I used that symbol. ::) I meant ~1.5 seconds. Also, It needs the strength to hold its own weight by ~1 second (got it right this time), and needs to be entirely gone ~2 seconds later.
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Is there an additive that would make it more easily evaporated?
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I did some more research, and it looks like water would be an appropriate solvent. Would this work?
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Water for very thin wires and at heat? Methanol definitely evaporates faster. You can experiment with a brush, PVOH in solution, and a piece of flat metal. I'd say: water at room temperature takes >1.5s in film thickness. Additive to evaporate faster: no, I don't think so.
You mention graphene oxide: do you realize that such materials are lab curiosities made in sub-nothing amounts? Standard reinforcements include graphite fibres, which are industrially available and can be very short.
PVOH is a bad construction material because it dissolves in water, including sweat. And I fear you overestimate its mechanical strength.
Did you consider polystyrene, or less brittle ABS, dissolved in acetone? At least these are sound materials. Beware of explosive solvent vapours.
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What about using boric acid to crosslink the PVOH?
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What is a solvent that would evaporate chloroform the second it touches air?
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Chloroform by itself evaporates easily, why do you want to complicate things using additional solvent?
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@dylanail
Is this thread related to your other thread
http://www.chemicalforums.com/index.php?topic=82450.0
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@dylanail
Is this thread related to your other thread
http://www.chemicalforums.com/index.php?topic=82450.0
Why not merge the two threads? I just did.
Briefly, adding a solute to something cause boiling point elevation, according to colligative properties. https://en.wikipedia.org/wiki/Colligative_properties
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The two threads were unrelated. Thanks though!
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Boiling point elevation can be understood as a colligative property and almost independent of the nature of the solute, but there is a major exception.
If the solute has a significant vapor pressure of its own then the boiling point of the solution most definitely depends on the nature of the solute. In the ideal case the total vapor pressure of the solution is just the vapor pressure you would expect from a mole-weighted average of the constituents vapor pressure.
https://en.wikipedia.org/wiki/Raoult%27s_law (https://en.wikipedia.org/wiki/Raoult%27s_law)
BTW many colligative properties must have similar such exceptions. They must in order to account for cases when the solute is identical or near identical to the solvent because, in such cases, there should be no expected deviation. For example, if I increase the molecular weight of oxygen in water from 16 to 18 to make so-called 'heavy-oxygen water' then I expect the freezing point to be essentially the same for both water and it and also for any mixture of the two.
In the case of boiling point the relevant property of the solute we do actually care about it is volatility. In the case of freezing point it is the miscibility of the solute in the solid phase of the solvent. (The difference here is due to the fact that all gases are miscible with one another whereas very few solids are miscible)
Anyways, it is quite possible for the boiling point of a solution to be below that of any of the constituents. At least it is if we assume the components manage to mix despite not being highly attracted to one another, so that it is actually energetically easier for particles to break free of the bulk liquid. It isn't hard to imagine that this is possible thanks to the rather chaotic character of liquids at a molecular scale, but only to a degree. Inevitably at some point the relative lack of mutual attraction will cause immiscibility.
Chloroform will form a positive azeotrope with methanol and ethanol. Unusually the effect might actually be large enough to be useful in the case of methanol:
Chloroform BP=61.1 ˚C
Methanol BP = 64.7 ˚C
87.4% (by weight) Chloroform + 12.6% Methanol (Azeotrope) BP=53.5 ˚C
https://en.wikipedia.org/wiki/Azeotrope_tables (https://en.wikipedia.org/wiki/Azeotrope_tables)
However, just because the boiling point is lower does not mean we have improved on the evaporation rate of of pure chloroform. If methanol evaporates sufficiently slower then chloroform and if there is enough of it in the solution then the solution could potentially evaporate slower as well.
I don't claim to understand evaporation rate stuff well and there is fair amount of methanol in there by mole so as far as I know it really could go either way.