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Chemical Eye on Oil and Water


May 18, 2010

Here's something you don't see on live TV every day - a portable classroom was submerging into eastbound traffic that was bobbing up and down on I-24 between Nashville and Murfreesboro.

As surreal as that image was, it was just the beginning of a historic two-day monsoon that literally swamped large portions of Middle Tennessee, drowning ten people just in Nashville and dissolving untold amounts of uninsured home equity.

Water is an incredible solvent, for instance it can dissolve more than its weight in sodium hydroxide, also known as lye or caustic soda. But it can't dissolve mineral oil, hence the saying that oil and water do not mix. They don't mix in a test-tube, and apparently they don't mix very well on the boob-tube either. I say that because while Nashvillians were swimming for their lives across interstates, the nationally televised news coverage was focused on the thousands of barrels of oil - per day - that were gushing out of a ruptured well on the floor of the Gulf of Mexico, with no end in sight but the delicate estuaries of Louisiana ominously down-current.

jpg The Grand Ole and water don't mix either

The Grand Ole and water don't mix either, but they are easily parted when artists are determined and alternative venues are generously offered. Source:

While the water was rising in Nashville, there was another big story breaking in New York City. The unexploded car-bomb found in Times Square, and the Connecticut jihadist who put it together, were headline news in print and on TV for days. This story, unlike the water-based one, seemed to easily blend with headlines about the oil-gusher in the gulf. Perhaps the chemical metaphor explains this better than the regional bias that was widely blamed by Tennessee bloggers: The Times Square would-be bomber had ties to Pakistani Taliban, who are in league with al-Qaeda, which has the Saudi Osama bin Laden at its head. In other words, the bomb story was oil-based.

To get back to chemistry, oil and water don't mix, but they do form an emulsion. And that's where Anderson Cooper comes in. He brought the attention of mainstream news to the floodwaters of Nashville, even while the gushing in the gulf seemed to worsen.

Anderson Cooper has also done wonders for the hair gel industry, but gels are structurally different than emulsions. Gels have "body" because they contain very long polymer molecules that are cross-linked with each other, forming a kind of scaffold at the nano-scale. The many pores can be filled with compounds that have either cosmetic or medicinal purposes. They can also be left empty, as in aerogels that can be made into curious solids that are lighter than air and described as solid smoke.

Emulsions on the other hand, are homogenized liquid mixtures made from two or more immiscible liquids, such as oil and water. For instance, olive oil and vinegar, which is mostly water, form an emulsion when shaken vigorously. You might call it salad dressing, but I call it chemistry, which is my bread and butter. If you let this mixture sit for a while, it will separate into two liquids, with the oil layer floating on top.

To prevent this from happening, or to stabilize the emulsion, surfactants are added to the mixture, and this is the only purpose of many of the odd-sounding ingredients that you see on bottles of salad dressing or shampoo, such as sodium laurel sulphate. Without going into much chemical engineering, these surfactant molecules like being at the interface of the two immiscible liquids, but try to keep their distance from each other.

Until the gushing of oil could somehow be stopped in the gulf, one of the methods initially used to mitigate the environmental catastrophe that would occur if large amounts of oil were to reach the wetlands was emulsification. At the milligram level, surfactants are quite a useful trick, but at the tonnage level needed to disperse the oil that was not mixing with the gulf waters, even the oil industry's environmental engineers had their doubts.

Nobody is sure what's in store for the gulf coast, but we will certainly learn a lot about the chemistry of mixing oil and salt water.

The floodwaters are still receding in Nashville, but the clean-up is well underway. The stage of the Grand Ole Opry was underwater on Tuesday, May 4, but "the show must go on" is another saying, and it did, on higher ground.




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Chemical Eye On... Columns by Preston MacDougall

Preston MacDougall is a chemistry professor at Middle Tennessee State University. His "Chemical Eye" commentaries are featured in the Arts and Public Affairs portion of the Nashville/Murfreesboro NPR station WMOT (

Preston MacDougall ©2010

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