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Mixing the Unmixable
markthebrewer writes "From an article in the New Scientist: Conventional wisdom every 15 year-old knows says that you can't mix oil and water without some kind of surfactant. However a team lead by Richard Pashley from the Australian National University in Canberra have done it simply by first removing all dissolved gases from the water. Apart from the obvious potential improvements in salad dressings, it could have an impact on the manufacture of everything from drugs to paint - anywhere an emulsion is required. Apparently, it will also give some insight into the mysterious 'long-range hydrophobic effect' (or why oil droplets coalesce over surprisingly long distances)." Keep in mind the usual scientific caveat: this experiment doesn't seem to have been replicated by other experimenters yet.
But where are these 15-year olds who know what a surfactant is? :)
My dingo ate your honor student.
What the environmental impact of water based oils will be.
It's like mixing oil and water, assuming that all of the dissolved gases haven't been removed from the water.
Yeah, that rolls off the tongue.
Can we say Pons and Fleischmann salad dressings?
"Yeah, we were like oil and water without a sulfacant!"
Scientists mix oil and water.
In other news, record sub-zero temperatures in hell.
"Times have not become more violent. They have just become more televised."
-Marilyn Manson
"He takes the air out and he doesn't get the long-range hydrophobic force. It doesn't nail the hydrophobic force down, but now we have something to work on," says James Quirk, a chemist at the University of Western Australia in Perth..."
Hydrophobic, eh? So that's the reason they don't mix: the oil is afraid of the water. Neat.
PS I wonder if the chemist's middle initial is T.
I want to drag this out as long as possible. Bring me my protractor.
>> "...simply by first removing all dissolved gases from the water."
Ahhh, Once you remove all of the Hydrogen and Oxygen I can see where there would no longer be a problem!!!
Great, hopefully Alton Brown can make a super mayonnaise emulsion based on this theory - super tasty and smooth on the tongue, now that's Good Eats!
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Esobofh - Currently drinking fresh mango juice.
This has got to be a dupe. Think of all of the biological effects that would be couteracted by this. Hydrophobic/hydrophilic effects are the basic reason why proteins fold the way that they do, and biological system's don't have free gasses floating around. Not to mention what would happen to all of our membranes (note, membrane formation is also due to hydophobic/hydophilic effects). Gasses in a biological system are all bound to something - example - Oxygen is bound to hemoglobin or myoglobin, if it isn't it causes serious problems. If water and oil mix without gasses present then we're in a world of hurt and I'd just be mush right now instead of typing this.
From the article...
An alternative might be to disperse the medicine in degassed water, which is already produced on a large scale by the oil industry.
You're telling me the oil industry itself makes degassed water on a large scale - for some unmentioned reason - and didn't discover this researcher's claims that oil and degassed water spontaneously emulsify? What's up with that?
---If you can't trust a nerd, who can you trust?
The effect prevents oil's dispersion in water, and means that you can only make oil and water emulsions, such as French dressing for salads, by shaking them and adding stabilising agents. ?
Second of all, the oil/water thing is more of an Italian dressing, I believe; and First of all, we don't call it french dressing any more, we call it Freedom Dressing.
I'm an American. I love this country and the freedoms that we used to have.
how exactly is "mixing" defined? If I put olive oil and tap water in my blender, and crank it on high, it is pretty well mixed, at least temporarily. Is it critical that the "mixture" stay "mixed" over time?
"And this is my boy, Sherman. Speak, Sherman." "Hello." "Good boy."
Here's the link to the actual journal his article was published in, for the curious.
From the article, it would be a stretch to say that Pashley has found a way to overcome "long-range" hydrophobic effects. Those effects are still present. However, he has found a way to get the hydrophobic liquid to break away in small droplets. Once broken away from the bulk, standard DLVO theory takes over to keep the particles apart. DLVO is not a cancelation of hydrophobic effects, it is just an overpowering of hydrophobic effects by electrostatic effects.
Unfortunately, it seems as though Pashley has no good explanation for why the degassing method works, it just does. This could be interesting, as more researchers study the role of gasses in keeping hydrophobic and hydrophilic liquids apart.
Overall, quite interesting, though New Scientist does tend to exagerate scientific findings.
Tony
The question is not "why doesn't oil dissolve in water?" The answer to that is obvious; water attracts other water molecules significantly better than it does oil, so it tends to exclude the oil. However, the effects of simple water-oil vs water-water interactions are only visible over a very short range.
The problem here, as far as I understand it, is that if you put two small droplets of oil far away from each other on a water surface, they'll tend to meet up sooner than you would expect just from random movement. There's nothing obvious from orgo that says why that should happen.
I think the /. article is a little misleading. After scanning the JPhysChem B article here (You may need to have a license). The articles suggest that removing dissolved gasses allows you to mix oil and water indefinately. I'm pretty sure that this is not true.
/. article.
They are adding 2 ml of oil and 33 mils of water and after mixing they still have some oil phase (from the picture in the paper). They are reporting an increase in the solubility, not that oil and water in these conditions are completely miscible as implied by the
As for my questions, I'm not sure I understand their results with respect to the observation that re-exposure to air doesn't immediately reverse the effect. This sort of raises a red flag to me, because (assuming there isn't any covalent chemistry going on) it means that achieving equilibrium is rather slow, and it may be that they are not at equilibrium when the measurements are made. Either way it is an interesting paper. (This would be better phrased as a question than a statement, I might have just missed the answer in the paper....)
-Sean
Scientist: I've done it. I've DONE IT! Two parts gin ... one part vermouth ... and an olive. They MIX! Mwuahahaha!
Grad student: Uh, that's just a martini, and not a very dry one.
Scientist: Blast! Well, bottom's up. We'll just change gin to "oil" and vermouth to "water" and publish anyway.
You folks are missing the key point in the article:
"The mix spontaneously formed a cloudy emulsion".
This is very different from the usual case where you take an oil and water mix and maybe some surfactant and agitate it.
The reason is that the formation of surface area during the dispersion of oil into water normally requires an energy input. Surfactant reduces the energy required and also often stabilizes an emulsion by adding some repulsive forces (either steric or electrostatic) between the droplets. However, with the exception of systems called microemulsions that increased surface area always represents a energy increase. With time (the amount of time depending on the use of suractant etc.) that free energy will cause the emulsion to break and form two homogeneous layers.
Microemulsions are the exeception; they are unusually favorable systems that reduce the energy of formation of surface area to near zero, probably less than the thermal energy kT available. Thus they can spontaneously form emulsions that are stable indefinitely. Microemulsions generally require very specific compositions to form so they are not often seen except in some specialized applications.
The problem with Pashley's work is that he is claiming the spontaneous formation of an emulsion.. This would normally be expected only if the surface energy of his mixture was near zero - and there is nothing in the description of this system to indicate that this is happening, regardless of the side show with air bubbles.
What is more likely is that his oil-water system actually contains some small amount of surfactant as an impurity (quite typical in many oils). If so, the process of lowering temperature will take this mixture through what is known as the phase inversion temperature, where the mixture will achieve a minimum surface tension. This lowered usrface tension will make formation of an emulsion with minimal energy input quite likely.
methodology: I boiled a cup of water in the microwave. I waited for it to cool, and boiled it again. I let it cool and boiled it again. I carefully removed the cup and let a few drops of (extra virgin olive) oil drip onto the surface from about 1cm height to minimize air bubbles.
observations: the oil stayed in a tight slick on the surface for about 10 seconds. Then it spread out, I'm assuming because of the heat of the water.
After a about 45s, a piece of wood was introduced to the water, which caused mild boiling suggesting that the water had indeed been devoid of air.
After more than 30 mnutes, the slick was still on the surface without mixing.
Conclusions: those guys are need to accumulate more data.