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If you have ever tried to make a salad dressing, or even tried preparing a pharmaceutical emulsion, this is for you. Or if you have ever noticed or heard the saying "oil and water don't mix", then this is for your education and the betterment of salad dressings worldwide.

No, I don't believe you! Science proves that oil and water can't mix!

Go to your kitchen. Right now! Get oil. Get water. Combine them. See! They don't mix. Instead, the oil clumps together in droplets. A usually sufficient explanation consists of hydrophobic and hydrophilic ends of the molecule.

One scientist was not convinced of the simplicity of this apparent truth. Professor Ric Pashley from the Department of Chemistry at the Australian National University was puzzled by this, and set out to find the answer. In 1982, he discovered a force he named long-range hydrophobic force. This is now accepted as why oil and water do not mix. It seems that the oil droplets can attract each other from distances as large as their own radius. This explains why they clump together instead of dispersing. Any other two liquids would disperse according to principles of entropy and such related science.

Pashley has done some other research on the properties of water once you remove the gases dissolved in it. He found that since the gases didn't fit well with the water molecules, the gas molecules tended to stick with the other molcules in the water. Gas molecules appear to have an affinity for hydrophobic molecules, like oil.

When you agitate the mix, small oil droplets try to break free of the main body. However, the presence of the gases creates negative pressure between the droplet and the main oil body. Gas pockets or cavities form between them. This process is called cavitation. This pulls the oil droplets back towards each other.

The obvious conclusion was drawn. If the gas is there, oil will never mix with water. What if you remove the gas?

The hypothesis was that if the gas, major factor in the cavitation, was removed from the oil and the water, cavitation would not happen. With no cavitation, oil will form smaller droplets and possible create an emulsion.

So, how do you do it?

De-gassing water is an easy industrial process. All you need is liquid nitrogen and a vacuum pump. Simply freeze the water and suck the gas out as it thaws. Then add oil and mix as a standard emulsion. However, if you are at home, and do not have liquid nitrogen and a vacuum pump, then do not fret. stick it in the freezer, then thaw. It yields satisfactory results. Do not do this if you are in a hurry! It takes a long time.


Afterthought: I wonder what this means for cryonics, since every cell has a phosphlipid bilayer as a cell membrane. Surely lipids would behave in a remarkably similar fashion, just like oils and cell membranes react to detergents similarly.

It has been asked whether boiling water would yield the same result. I would say yes. It has also been mentioned that water is rarely if ever used in salad dressings. This is true, and the above mentioned method yields unsatisfactory salad dressings, but satisfactory emulsions. It has also been asked whether freezing vinegar would make a good emulsion. I have no practical experience here, so I will hypothesize with my meagre knowledge of chemistry. Vinegar (acetic acid) is a dimer, meaning two molecules are stably bonded together in vinegar solutions. Apparently, it will mix well with oils, and freezes easily as well. So it could work

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