macckone
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PVA film diaphrams
Has anyone actually played with PVA films?
These have been proposed as an alternative to Nafion films.
The literature I have found suggests that starch/PVA/Borax is very good.
The formula is 50% starch and PVA, then 30% glycerol is added.
This is heated at 80C for 2 hours then borax is added and a film is cast.
I am wondering how this would perform with agar agar in place of starch.
I haven't found any references regarding this type of substitution.
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Fulmen
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Funny, I'm reading up in the same thing. But it's not a diaphragm but rather a proton/cation permeable membrane. A diy anion membrane would be
interesting as well.
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DrP
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Out of interest - do you mean PVA to be Polyvinyl Alcohol or Acetate? People seem to use it for both these days somehow.
\"It\'s a man\'s obligation to stick his boneration in a women\'s separation; this sort of penetration will increase the population of the younger
generation\" - Eric Cartman
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macckone
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Fulmen:
Making it anion or cation permeable only seems to be pretty difficult.
There is at least one with PVA/TiO2 that was supposedly anion only but not sure what the selectivity is.
DrP:
PVA - polyvinyl alcohol
However polyvinyl acetate would be good as well.
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Fulmen
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I believe the PVA/borax mixture could work as a cation membrane. The borate anion crosslinks with the PVA, but cations should still be mobile.
Edit: I'd also like to see the reference on that procedure. The thought of making functional ion membranes from PVA, starch and borax sounds amazing.
[Edited on 9-10-18 by Fulmen]
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macckone
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the key factors seem to be solubility of the pva and selectivity.
sulfone compounds seem to be pretty selective but also harder to get.
titanium oxide was one of the recommended compounds that gave good selectivity.
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BaFuxa
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Quote: Originally posted by Fulmen  | I believe the PVA/borax mixture could work as a cation membrane. The borate anion crosslinks with the PVA, but cations should still be mobile.
Edit: I'd also like to see the reference on that procedure. The thought of making functional ion membranes from PVA, starch and borax sounds amazing.
[Edited on 9-10-18 by Fulmen] |
Actually I played with PVA membranes this summer.
Crosslinking is by far the trickiest part of the process. You need your membrane to hold up to your electrolyte.
Non-crosslinked PVA quickly dissolves in water, many laundry detergent baglets are made of PVA.
I tried boric acid, sodium borate, citric acid, freeze thaw. You need at least a milimeter of thickness if you want your membrane to survive the
electrolyte. The only one I made that hold up to 24 h in a KOH solution was about that thichness. Everything thinner than that just dissolved away.
What you do is you dissolve your PVA and crosslinking agent in water at about 85°C, let it dry at RT or under moderate heat. Then heat the film up
with a heat gun until it hardens, then you soak it up in a KOH to "dope it" if you want an anion exchange membrane. It gives you a brown/ reddish
brown plasticky membrane.
I broke up my membrane to pieces so I cannot report on its electrochemical performance. When you dry it it becomes less plastic and more brittle ;
some papers recommend using glycerol as plasticizer.
What I wanted to try next was increasing the crosslinking strength by using something stronger than hydrogen bonding. Some papers use formaldehyde,
and even epoxy groups grafted onto the PVA.
[Edited on 25-10-2018 by BaFuxa]
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