[jiuning]

Hi All,

I need help from you guys about PVA water solution. I did try to disolve PVA (Mw 89,000-98,000, 99+% hydrolyzed Poly(vinyl alcohol) powder from Sigma Aldrich), but I failed. I am describing the method I used, could you guys please point out what I did wrong?

Currently I heated a bottle with 10 ml water at 98 degree C and keep stir at 300 rpm, then I slowly add 1 gram of the above PVA powder into it. After keep heat and stir for 4 hours, I stop heat and stir. Then a few minutes later, white soft staff appeared at the bottom of the bottle. I tried to spin coat the solution on silicon, but I got very non-uniform film. I can see big grains (about 0.5 mm) composed of the film. After drying the film, the film becomes very fragile.

My objective is prepare less than 10 um thick uniform PVA film on silicon substrate. But right now I even couldn't get uniform PVA solution to start with. I am wondering if you can provide me some help on preparing PVA solution of ~ 10 wt%. Thank you very much.

[enahs]

Polymers that big can take days to actually go into solution. Remember it is a diffusion process and diffusion is proportional to mass (among other things).


Also, believe it or not, often with larger polymers rapid stiring actually slows down the process (not always).

Conversely, if you need a lot of agitation for something to go into solution, sonicating is often better.


My solution, stir it gently (but thoroughly) over the weekend and see what you get Monday.


Also, is water the best choice for thin films?

[jiuning]

Thank you so much.

I will try your advices. I found on wiki and other papers that PVA is a water soluble polymer and good to dissolve in water. Also it seems that PVA water solution is extensively used in industry to produce thin films. If you have any other suggestions on the choices of solvents for PVA, please let me know.

Thank you.

Polymers that big can take days to actually go into solution. Remember it is a diffusion process and diffusion is proportional to mass (among other things).


Also, believe it or not, often with larger polymers rapid stiring actually slows down the process (not always).

Conversely, if you need a lot of agitation for something to go into solution, sonicating is often better.


My solution, stir it gently (but thoroughly) over the weekend and see what you get Monday.


Also, is water the best choice for thin films?

[Polytriazole]

Polyvinyl alcohol dissolves well in water, but not much else.  Be careful with your thin films, they will pull a lot of moisture out of the air and that will plasticize them, changing their mechanical properties.  The plasticization may also cause the films to deform, causing wrinkling or dewetting from the wafer.  Just keep an eye out for that.

As for making your solutions, molecular weights that high are going to take a long time to dissolve.  You may also find that you can't make a 10 %wt solution of PVA that is that heavy.  We usually don't use molecular weights like that at a concentration of more than a few %wt because the solutions get too viscous.

Follow the suggestion above of letting the solution stir for several days, gently, at room temperature and see what you get, it should work a lot better.

[jiuning]

Thank you so much for the great advices.

I am trying to stir the existing solutions. Meanwhile, I will purchase small molecular weight of PVA.

Polyvinyl alcohol dissolves well in water, but not much else.  Be careful with your thin films, they will pull a lot of moisture out of the air and that will plasticize them, changing their mechanical properties.  The plasticization may also cause the films to deform, causing wrinkling or dewetting from the wafer.  Just keep an eye out for that.

As for making your solutions, molecular weights that high are going to take a long time to dissolve.  You may also find that you can't make a 10 %wt solution of PVA that is that heavy.  We usually don't use molecular weights like that at a concentration of more than a few %wt because the solutions get too viscous.

Follow the suggestion above of letting the solution stir for several days, gently, at room temperature and see what you get, it should work a lot better.