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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.
Other people might know it as an emulsifier.
..There's a-dooin's a-transpirin'
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
"someoen ... mixed water with petrol and made his car 20 times more efficient."
This has been done by drag racers for years, and as another poster mentioned, was even used in spitfires in WWII. The reason it works is the same principal as a steam engine: hot water -> steam, expanding dramatically in the process, thus providing more pressure on the piston. However, the high temperatures in an engine cause some of the water to be ripped apart into H2 and O2, at which point the H2 can recombine to form highly acidic compounds that corrode your engine and reduce its operating life many times over. That is why it is not commonly used unless super-high torque is required from an engine NOW and you don't care how long the engine lasts after that.
Of course, there's still the other obvious problem of putting too much water in your gas...