Need a liquid with an extremely low surface tension

[silverpig]

I have easy access to acetone, ethanol, methanol, and isopropanol. They all have pretty low surface tensions, but I would like to know if there is anything significantly lower.

There are a few liquids I know about which are a bit better, but it has to be significantly lower in order to be worth the trouble, and they also have to be relatively non-toxic (fluorinated organics are out).

 

[RESmonkey]

I'm not going to ask WHY...
I can't contribute to the thread either, I'm not as knowledgeable...yet...
BUT...I can imagine this has something to do with either:

1. Filling this in a pool, and then diving into it, FLAT, and recording it. Then claiming it was water?
2. Shooting the liquid w/ bullets?

 

[esun]

Not a chemist, but this may prove useful: http://en.wikipedia.org/wiki/Surface_tension_values

That contains this link: http://www.surface-tension.de/

Perfluorohexane - 11.91

That's the smallest value I see in that list. Umm, nevermind, that appears to be a fluorinated organic...well, maybe you can find something else in the list.

 

[silverpig]

Originally posted by: esun
Not a chemist, but this may prove useful: http://en.wikipedia.org/wiki/Surface_tension_values

That contains this link: http://www.surface-tension.de/

Perfluorohexane - 11.91

That's the smallest value I see in that list.

Yeah I saw that, but it's fluorinated... and that's bad.


I work in a condensed matter lab and am making very small suspended gold bridges. The bridge is created in a wet etch (water + other stuff), and then blown dry. The surface tension of the water is enough to severely damage the gold bridges.

We have a critical point drier available (uses the critical point of CO2 where there is no distinction between liquid and gas phase), but I think my samples are too big to fit in it.

My hope is that using a transition liquid with a low surface tension will mitigate the damage without having to resort to travelling to another critical point drier.

It looks like methanol it is for me.

 

[CycloWizard]

Surface tension isn't dependent only on the liquid, but also on the surface you're wetting/not wetting. If you want something with a very low surface tension on most metals, look to penetrating oils (such as liquid wrench). I'm not familiar with their behavior with gold as far as surface tension or solubility goes, but these oils will generally completely wet most common machining metals (i.e. have a contact angle approaching 180° or 0°, depending on how you look at it). You can pick them up in a relatively high purity container at any hardware store for pretty cheap, too, though the purity might not be as high as you'd like for this application.

 

[BladeVenom]

Originally posted by: silverpig

It looks like methanol it is for me.

? Ethanol is lower and less toxic.

 

[silverpig]

Originally posted by: CycloWizard
Surface tension isn't dependent only on the liquid, but also on the surface you're wetting/not wetting. If you want something with a very low surface tension on most metals, look to penetrating oils (such as liquid wrench). I'm not familiar with their behavior with gold as far as surface tension or solubility goes, but these oils will generally completely wet most common machining metals (i.e. have a contact angle approaching 180° or 0°, depending on how you look at it). You can pick them up in a relatively high purity container at any hardware store for pretty cheap, too, though the purity might not be as high as you'd like for this application.

I don't want anything to penetrate. This work is done in a cleanroom and blowing oils around with an N2 gun is probably frowned upon

 

[silverpig]

Originally posted by: BladeVenom

Originally posted by: silverpig

It looks like methanol it is for me.

? Ethanol is lower and less toxic.

It's marginally lower *shrug*

We use methanol and isopropanol a lot; ethanol is a bit rarer and more expensive because we have to use the non-denatured stuff.

Meh, I'll be doing a test today so it might be moot.

 

[CycloWizard]

Originally posted by: silverpig
I don't want anything to penetrate. This work is done in a cleanroom and blowing oils around with an N2 gun is probably frowned upon

It's only called 'penetrating' because it wets extremely well due to its low surface tension. This good wetting enables it to find its way between threaded parts where other liquids couldn't, which allows you to un-freeze nuts and bolts, for example.

Are you sure that the damage is being caused by surface tension and not the evaporation rate? Just a thought. I sat in on a seminar on this subject a while ago, but I'd have to dig through my notes to recall what the guy found out. It was too boring to remember, but interesting enough to write down.

 

[silverpig]

Originally posted by: CycloWizard

Originally posted by: silverpig
I don't want anything to penetrate. This work is done in a cleanroom and blowing oils around with an N2 gun is probably frowned upon

It's only called 'penetrating' because it wets extremely well due to its low surface tension. This good wetting enables it to find its way between threaded parts where other liquids couldn't, which allows you to un-freeze nuts and bolts, for example.

Are you sure that the damage is being caused by surface tension and not the evaporation rate? Just a thought. I sat in on a seminar on this subject a while ago, but I'd have to dig through my notes to recall what the guy found out. It was too boring to remember, but interesting enough to write down.

Nothing is evaporating. I'm physically blowing the liquid off with an N2 gun.

 

[dkozloski]

Liquid helium at near 0deg K. becomes a superfluid with a surface tension so low it moves up and over the sides of a container or pours out of microscopic holes.

 

[f95toli]

I assume the reason you are using it now is because yuou want to remove the etchant quickly.
What if you just put the chip in a mild ultrasonic bath in some isopropanol? That should remove the etchant pretty quickly-
IPA is usually a good choice because it is quite clean and evaporates without leaving any trace, if you use methanol you might have to remove any residues using IPA anyway.

 

[silverpig]

Originally posted by: f95toli
I assume the reason you are using it now is because yuou want to remove the etchant quickly.
What if you just put the chip in a mild ultrasonic bath in some isopropanol? That should remove the etchant pretty quickly-
IPA is usually a good choice because it is quite clean and evaporates without leaving any trace, if you use methanol you might have to remove any residues using IPA anyway.

The etchant is 10:1 BOE (5% hydrofluoric acid with an ammonium fluoride buffer) to etch silicon dioxide. The etch rate is 600 A/min (ie slow).

Removal of the etchant is to dip it in a DI water stop bath which dilutes it to a negligible amount. The problem here is I have a very delicate suspended gold nanostructure which is destroyed by surface tension of the removal of the water.

I tried moving the sample to methanol after the water and then blowing that off, and it worked a bit better, but I still wanted something to improve on that with. IPA would be about the same.

We usually blow dry with N2 as opposed to letting it dry because even IPA and methanol leave a very small bit of residue usually. They're infinitely better than acetone, but it you can still see stuff on the samples.


It's a moot point now though, as I now have easy access to a critical point drier. For those interested, you put your sample in the machine immersed in IPA (isopropanol in case someone doesn't know), and seal the chamber. The machine then pumps in liquid CO2 to purge the IPA, and then increases the temperature of the liquid CO2 to the critical point of ~30 C and 1350 psi. At this point the liquid and gas have the same properties. It then reduces the pressure and turns all the CO2 to gas at once, then pumps it out and returns to atmospheric pressure. No surface tension, no evaporation, just fun

 

[gsellis]

Late to the game, but a different tack?

Light Water... that agent is used by fire fighters for fuel fires like gasoline. Breaks surface tension so that gasoline does not "float" and gets extinguished. Also makes ducks, like those in the Peabody Hotel, sink, if added to the fountain by drunk firefighters that might have attended a conference there. Quack, quack.

Found one link link to a toxicity study. Propylene Glycol maybe as a WAG?

 

[RayH]

How about freeze drying in vacuum chamber?

 

[silverpig]

Originally posted by: RayH
How about freeze drying in vacuum chamber?

I don't want the liquid frozen to my structure

 

[NeoPTLD]

What about n-hexane? Pretty common stuff.

 

[Check]

Originally posted by: silverpig

Originally posted by: BladeVenom

Originally posted by: silverpig

It looks like methanol it is for me.

? Ethanol is lower and less toxic.

It's marginally lower *shrug*

We use methanol and isopropanol a lot; ethanol is a bit rarer and more expensive because we have to use the non-denatured stuff.

Meh, I'll be doing a test today so it might be moot.

I guess purchasing a handle of grain alcohol isn't going to cut it for this experiment.

 

[Nathelion]

What about putting the bucket of water in a vacuum chamber, then evacuate the chamber, and keep going until almost all the water is gone? Then you could let the rest evaporate, and no damage right? It might be time consuming, but it might also work. The water would turn into gas once the pressure falls below a certain point... of course, it might also melt. I suppose you could have a light source that peaks in a part of the spectrum where some appropriate water absorption lines are located...

 

[silverpig]

Originally posted by: Nathelion
What about putting the bucket of water in a vacuum chamber, then evacuate the chamber, and keep going until almost all the water is gone? Then you could let the rest evaporate, and no damage right? It might be time consuming, but it might also work. The water would turn into gas once the pressure falls below a certain point... of course, it might also melt. I suppose you could have a light source that peaks in a part of the spectrum where some appropriate water absorption lines are located...

That's the point though... when it evaporates the volume of water gets smaller until it's about the size of the nanostructure. At this point surface tension takes over and starts breaking things.


The critical point drier works well now anyways.