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Author: Subject: Suitable Surfactant Recommendation
glueshooter
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[*] posted on 4-9-2008 at 21:27
Suitable Surfactant Recommendation


Hey everyone, I'm new to this board and I'm hoping you can help me. I design printable ink binders, and I've been asked to make a formula based on sodium silicate (water glass). I've been able to make various mixtures of industrial grade products and water and find a good viscosity, but surface tension has been a problem.

I usually use a glycol-ether for this in the carbon based formulas, but no matter what I do, two things happen when I add it. First, the silicate starts to gel. I can control that to some extent by adding a drop of ammonia to keep it basic, but it's never just right.

The bigger problem is the difference in density. The Na/Si I'm using has a density of ~1.4, while the density of the butyl cellosolve is only .9. It more or less puddles on the surface, and looks like small oil slicks. I've tried premixing it with other glycols to see if it will stay in solution, but it just won't.

I'm trying to get at least as low as 40dyne/cm^2, but would prefer to go even lower. I only have one liter of the water glass to play with, and then I have to buy a 55 gal drum. I really don't want to keep taking shots in the dark, as I'm not getting anywhere with that approach.

By the way, I also tried silicon oil, a micellular type of surfactant, and something called triethanalomine (I'm sure that's spelled wrong; it was something we had laying around that claimed to be a surfactant. It was a heavy, syrupy stuff).

Any help is greatly appreciated; I thank you in advance.
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not_important
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[*] posted on 4-9-2008 at 23:35


The alkali silicates are quite different than most organic you've likely worked with. Reducing the pH will result in the formation of silica gels, ammonia really isn't a strong enough base. Adding anything that interferes with the interactions between water and the silicates also will cause gel formation. Dilution and adding a small amount of alkali (NaOH or KOH) is the usual way to reduce viscosity and surface tension, and organic that will mix with water probably should be keep to rather low concentrations to avoid gel formation caused by dehydration. Amines, such as the triethanolamine might if used in small amounts, alkaline surface agents also could be tried - sulfonates for example.

I think your best bet is to go to a different silicate. There is an entire family of them, with differing ratios of "Na2O" to SiO2 and a range of properties. Note that generally a lower Si:Na ratio will have a lower viscosity and a higher pH. Find one that is closer to your needs, after that perhaps try adding modifiers.

http://www.pqcorp.com/productlines/sodiumsilicatespecs.asp

http://www.oxy.com/Our_Businesses/chemicals/Documents/silica...



[Edited on 5-9-2008 by not_important]
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glueshooter
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[*] posted on 5-9-2008 at 05:36


Thanks for the tips. The sample I have is actually Oxy's JW-25, their low viscosity version. Like I say, modifying that hasn't been too much of a problem. I have a great two stage DI water system, and I routinely get 50MOhm water. So I really don't have issues there (at least that I can see).

I didn't know chemicals like KOH and NaOH work as surface tension modifiers. Everything I do is water based solutions, so I use things like PVP, PVA, and sugar for making the glues. I'm a physicist, not a chemist, but these issues just sort of got dumped in my lap a few years ago and I've been learning ever since. Thanks again.
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[*] posted on 5-9-2008 at 05:54


The strong bases are more for stabilizing the silicate than surface tension modification. The strongly basic conditions of the alkali silicates will make it more difficult to find a surface agent that is stable, as will the tendency to cause the solution to gel.


For treating concrete with soluble silicates:
Quote:
Add surfactants, these are surface-active agents that reduce the surface tension of the silicates. It is important that a nonionic or anionic surfactant that is stable at high pH (>11) be used. Generally, 0.05% of surfactant by weight of silicate is sufficient to increase penetration.

and treating wood to provide fire resistance
Quote:
Surface tension was adjusted in all the
solutions with sodium dodecyl sulphate to 38 dyne·cm
although they were using pressure as well.

Also
http://www.pqcorp.com/TechnicalService/..%5Cliterature%5Cbin...
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[*] posted on 5-9-2008 at 05:57


There are a range of surfactants by BYK and BIOWET which work well with sodium silicate to reduce surface tension, viscosity and to improve flow.

EDIT: I just checked - sorry it was the BIOWET ones which were compatible.

[Edited on 5-9-2008 by DrP]




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[*] posted on 5-9-2008 at 12:16


Thanks again for the help. I have a question about the SLS. I saw that its density is close to water, right around 1. Do you think I will have the same problem with it coming to the surface because of the density difference?
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[*] posted on 5-9-2008 at 16:07


I am curious about the application for this medium. Is it printing on ceramic or glass, perchance?
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[*] posted on 5-9-2008 at 17:42


Quote:
Originally posted by glueshooter
Thanks again for the help. I have a question about the SLS. I saw that its density is close to water, right around 1. Do you think I will have the same problem with it coming to the surface because of the density difference?


Shouldn't be as it is miscible with water. Notice the small concentrations used, I'd thin it a bit with water, then stir it into the silicate. Could even thin it, add a bit of the silicate and mix well, then add that to the main batch.
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[*] posted on 7-9-2008 at 08:00
Use SDS


SDS (sodium dodecyl sulfate) is the way to go; the alternative is SOS, but it is very expensive
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[*] posted on 7-9-2008 at 19:39


Thanks everybody, for weighing in. I have some samples coming and I'm looking forward to trying it out.

DrP - I'm not searching for biowet properly or something. I can't get a lead on it.

watson - All I can say is, umm, maybe
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[*] posted on 12-9-2008 at 06:38
Now I need a defoamer


Hey everyone. the SDS came this morning, and I mixed a batch close to the micelle point. The surface tension did indeed drop to ~37dy/cm2, but there's a new wrinkle. It is very very foamy. What can I do about that, while still keeping the fluid both basic and a solution?

Thanks again.
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[*] posted on 12-9-2008 at 06:44


A few % high alcohol, like n-octanol might do the trick? I know it commonly used to reduce foaming, but i guess it will increase surface tension!



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[*] posted on 17-9-2008 at 10:46


I just happened to have some octonal in the lab, so I gave it a shot. Maybe I have to up the %, but I'm not sure how high to take it. I found in a reference book that Octanol and H2O have a maximum solubility of 0.059g/100gH2O. I don't know the accuracy of that.

I made 50g H2O + .2gSDS and it's foamy
I made 50g H2O + .2gSDS + .02gOctanol and it foams, albeit slightly less.

Any other things I could try?

Thanks again!
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[*] posted on 17-9-2008 at 15:52


With the high content of dissolved solids in the waterglass, you may have a difficult time getting much more octanol to dissolve. If it doesn't do the job, you could try C6 alcohols, or look into a anti-foaming agent, or look for a low-foam wetting agent. Just try to keep the organic content low, else you may cause the waterglass to gel.

The amount of SDS sounds somewhat high, you might try 1/20 that, then if it doesn't do the job add more on up to 0,1 (seeing as twice that works) testing with each addition.
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[*] posted on 18-9-2008 at 11:59


That was a good insight, so I made this:
50g(H2O), .030g(SLS), .020g(Oct). Surface tension was 26! I have not added this premix to the Na/Si yet.

Anyway, the foaming got to be much less, almost under control. But this fluid has now become what I would call strange. I'm sure it's normal; I just don't get it. When I was dripping onto the petri dish of my tensiometer, it was like it de-wet itself. I started with a small puddle, and when I dripped more on, it sat on top of the puddle for a brief moment before joining the rest of the bulk. I've never seen that before.

The more I read about Octanol and what it's used for, the more I'm worried that this might not be the right type of defoaming agent. Any more thoughts?
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