question on surfactants in PVA

I'm using Elvanol 85-82 dissolved 10-20% in distilled water with 10%

91%I Isopropyl alchohol and about 2-3% glycerin with a few drops of carwash soap as a lens cleaner.

The viscosity and drying are pretty good but when I lay it down on glass it sometimes tends to bead up a little from too much surface tension ( I think). Interestingly it beads less as I repeat the process of cleaning so it appears that initially whatever oil there is on the lens is probably contributing to the problem. Moreover, I cleaned one lens carefully with methanol first and it doesn't bead.

I'm wondering if increasing the amount of carwash soap will help this problem or if it might be one of the other ingredients I need to increase or decrease.



Reply to
Mike Maas
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I'm not sure if I understand your problem correctly. Are you referring to something similar to "orange peel"?

In that case you could try and change the drying conditions (slower drying should reduce the effect), or you could use a tail solvent (a high-boiling alcohol or something similar).

Cleaning of the substrate does also help, because wetting is essential for the coating material to flow and produce a smooth surface. If you suspect an oily residue on the glass I would use acetone to remove it (better solvent than methanol). Ultrasound does help a lot.

It might help. Perhaps you should also give other surfactants a try (non-ionic PEG, silicone, ...). Too much surfactant will diminish the adhesion and cohesion of the coating.

BTW: what is "carwash soap"?

Regards, Oliver

Reply to
Oliver 'Ojo' Bedford

Some disjointed thoughts (disjointed as it is first thing Monday morning and the "alien blood" hasn't kicked in just yet):

Why is the beading a problem if you are getting the lens clean?

I also am as curious as Ojo is about the carwash soap. What is it and do you get it from a consistant supplier so that it always the same materials?

Beading can be caused by surface tension differences (the fluid has a higher surface tension than the substrate) and also by surface roughness - the lotus plant being perhaps the most widely known example of this. Are the lens dirty from fluids or solids?

Surface tension is a function of temperature. Is this consistent in your operation? Your formula also has a fairly large range for the PVA. This will change the surface tension of the fluid.


Reply to

The car wash soap was something I had sitting around. The ingedients consists of sodium dodecylbenzene sulfate, coconut diethanolamine amide, nonylphenyl ethoxyate 9.5 Mole ethylene oxide and Sodium Sulphate and H2O. It was the soap I found that seemed to have the least smellgood chemicals added. The recipe I was using called for Photographic wetting agents like kodak photoflo 200 and some other choices none of which I have.

I washed all the filters after application with isopropanol 91% again then reapplied and actually I think there was even more beading than before.

As far as cleaning goes, it cleans pretty well where it doesn't bead but not at all where it does since no cleaner is applied on those spots.

The whole idea behind this technique is to find a compound that will capture the dirt when the dried pva is lifted from the lens to avoid any rubbing of the glass surface. There is a commercial product available at $100/oz. I also tried some Elmer's school glue cut with H2O as well but it didn't really do much for fingerprints.

Right now I'm thinking of adding a little acetone to the mixture since I know that the commerical preparation contains acetone along with alcohol.

One other possibility is liquid CO2 for which I have not been able to find a home oriented solution.

Thanks for your assistance. I graduated in chemistry 30 years ago but never used it professionally and have forgotten almost all of it.


Reply to
Mike Maas

Now I understand what you are after. (By the way, Elmer's glue is the made of the "other" PVA - polyvinyl acetate - a precusor to polyvinyl alcohol. Polyvinyl alcohol is not made from vinyl alcohol monomer, as that monomer undergoes an enol rearrangement to formaldehyde. If you didn't know that, don't worry. Linus Pauling didn't win a third Nobel Prize because he forgot about enol rearrangments! But I digress.)

It seems like the cleaner the lenses/filter are, the worse your concoction works as evidenced by the IPA pretreatment leading to less wetting. In that case, you need to lower the surface tension of the fluid - more PVA, more alcohol or acetone, more surfactant. As Ojo suggested already, you might want to consider nonionic surfactants (dishwasher soap) as they are low/no foamers.

Do you have a good PVA mixing process? My favorite method is to mass out a combination of water and ice, disperse the PVA is the ice water and mix while the ice dissolves. It prevents the PVA from swelling too quickly upon initial contact with the water and then agglomerating into a big gelatinous mess.

John (who is now a lot less disjointed due to all those brominated vegie oils!)

Reply to

Regarding the mixing process I've been slowly dissolving it into the distilled water in a pyrex cup in a boiling pan of water. Seems to work ok. Added additional alcohol too quickly once and did get a glutinous mass but further stirring and heat evenually caused it to go back into solution. I'll look at dishwasher soap and get some acetone for the next batch.

I'm pretty sure from reading the spec sheets on the glues that the blue gel school glue which is water washable is pva based as they used a different name for the other glues pvac(?). Even the white school glue is pvac I think. But I've noticed that it is fairly common to use pva for the acetate so I could be wrong.

thanks again,


Reply to
Mike Maas

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