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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.
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!"
>> "...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.
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 oil-water mixture is probably also a metastable state. In the presence of any catalysts (in this case dissolved gases; in the case of biological systems this function could be taken over by proteins, salt ions, I-don't-know-what-else...) the oil molecules would condense and clot together. Oil droplets are thermodynamically stable only above a certain droplet size; the same is true for water droplets in the case of the supercooled gas. Without catalysts, the critical droplet size cannot be achieved.
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
There are many products where oil-based and water-based things need to be mixed together and where it would be a bad thing if they separated. You have probably seen the phrase "such-and-such used as an emulsifier" (sp?) on the ingredients of some food-products.
Real-world example of wanting something to stay mixed: Paint
Have you ever opened a can of paint that's been sitting around in your basememt or garage for a few years? Some of the resinous compounds separate from the base materials the same way that the Olive Oil in your blender will eventually rise to the top again once you turn it off. Paint is more viscous and is not simply oil and water, but the same forces are in play.
The end result is that there is certainly commercial need for things to stay mixed together over longer times.
The Digital Sorceress
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
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.