What is oil? Basically, it's the polar opposite of water. (OK, it's actually the non-polar opposite of water, chemistry joke!). A hydrophilic material is one capable of making transient hydrogen bonds with water. Hydrophilic molecules are polar - one end has a net positive charge and one end a net negative charge. Water is the prototypical hydrophilic material, with a slight positive charge on the end of molecule with the hydrogen atoms (mickey mouse's ear) and a slight negative charge on the oxygen (the head, as shown below). The total charge of the molecule is zero, but each end is slightly polarized.
That polarity makes hydrogen bonding possible. Like dissolves like: A hydrophilic material is soluble in water, while a hydrophobic material -- like oil -- is insoluble in water. Hydrophobic means water hating. Hydrophobic molecules are nonpolar - like oils.
Oils are primarily hydrocarbons. These are nonpolar molecules, so when you mix oil with water, the oil hangs out with the oil and the water hangs out with the water. This leaves a large glop of oil in the middle of the water, which (in addition to being really bad for the environment) is embarrassing.
When you're doing the laundry, the hardest stains to get out are the oily ones because the water in which you wash your clothes literally doesn't want anything to do with the oil. Special surfactants -- molecules with one hydrophilic end and one hydrophobic end - surround small globules of oil with the hydrophilic end pointing out. The surfactant is sort of a mediator molecule that allows the oil-encapsulated glob to be carried out in the rinse water. The strategy boils down to: get the oil to let go of the fiber, break it into smaller globules, surround it with surfactant and wash it out.
In the Gulf Coast, the oil is being treated with dispersants like DISPERSIT and COREXIT. COREXIT is the particular dispersant being used. COREXIT's active components include "light petroleum distillate" (hydrocarbons like mineral spirits and kerosene), propylene glycol (an alcohol and emulsifier, which facilitates the mixing of oil and water and is a primary ingredient in stick deodorant) and organic sulfonic acid salt. The dispersant is dumped on top of the oil. It breaks the giant oil glob into smaller globules, surrounds it with surfactants and disperses it out to sea. Dispersants don't remove the oil, they just break it up into smaller pieces so that it's not as obvious. Natural processes biodegrade the oil over time. Yuck. They've dumped about 190,000 gallons of this stuff in the Gulf at this point.
Ideally, you'd like to be able to separate oil from water, just like you remove fat from gravy. My favorite way of separating out the oil from the broth for gravy is to cool the mixture and let the fat solidify. Hard to do in the ocean, I know.
I tried cleaning up my oil spill on the counter with a paper towel. This works for about three milliseconds and then you're mostly just moving the oil around the counter. The paper towels absorb the oil quickly then they are no good. So you basically use up a lot of paper towels because you can't rinse them out and reuse them. So anything that absorbs oil but doesn't let it go again is a problem because it has to be disposed. On the other hand, that's better than just breaking it up and leaving it.
Some companies are looking to aerogels - gels with so many air pockets that they look like sponges, but are very lightweight. Aerogels pores can be treated to be hydrophobic, which is important because you want a selective mop. If it attracts oil and water, that's not as helpful as just picking up oil. Those technologies aren't ready for use yet. Even after proven effective for picking up oil, they have to be tested for effects on the environment and the animals in the sea.
Most of the sorbents currently being used to deal with oil spils are made from the polymer polypropylene. Selectivity (oil, but not water) limits what we can use in the ocean. Common sorbents for racetracks are clays with pores that suck up and hold oil. The problem with clays and clay substitutes is that they absorb water as well as oil.
Polypropylene is hydrophobic, so fibers absorb oil, but let water pass through. I understand that there is now a polypropylene fiber shortage and its price is going up because of the high demand. Another company, MOP Environmental, uses recycled cellulose fibers that have been surface treated to minimize water absorption. Like the polypropylene, these fibers are placed into mesh bags and formed into booms, sweeps, etc. that can be put in the water and later collected. One of the disadvantages of absorption is that the oil is absorbed so strongly onto the polypropylene, for example, that you can't get it out again. The whole assembly has to be disposed of.
The MOP product also includes some oil-digesting bacteria. I remember during the Valdez disaster people predicting that someday, we would just be able to release bacteria and they would clean up spills in moments. These aren't special bateria, really. Some soil-dwelling bacteria naturally eat oil. Actually, it turns out you can find naturally occurring bacteria that specialize in eating just about anything, from sugar to starch to detergents. A couple of years ago, a 16-year old found a bacteria that eats plastic lunch bags. The problem is producing enough bacteria to make a dent in the millions of gallons of oil in a reasonable time. Also, the specificity of the bacteria as to what oils they will eat can be a problem, as "oil" contains a huge number of different types of hydrocarbon molecules. Most of these bacteria are as picky eaters as three year olds.
One of the more interesting solutions proposed (aside from dropping trash in the pipe to block the oil) also involves using fibers; however, the fibers in question are human hair. Chicken feathers, straw, and wool have all been used to collect oil in the past, but human hair seems to work particularly well. A big advantage is that the oil is adsorbed rather than absorbed. Adsorbed oil forms a very thin layer - a molecule or two thick - at the surface of the hair. Because the molecules are only weakly bound, the oil can be removed, meaning the hair can be reused.
Hair is naturally rough, as shown in the scanning electron microscopy picture to the left. The overlapping scaly things are your hair's cuticle. (This clearly isn't my hair because I dye my hair and that roughs up the cuticle quite a bit. This hair is in pretty good shape) All the roughness is good, because that means more surfaces onto which oil can adsorb. Every notch and bump on the cuticle is more surface area for oil to adsorb on. A pound of hair can pick up a quart of oil in about a minute.
Given that people of different races and ethnicities have very different hair, I am curious as to whether there are any studies out there about whether particular types of hair are more useful at adsorbing oil than others. I couldn't find any in the scientific literature, but that doesn't mean it isn't worth it. After all, hair is a renewable resource.
Although there have been a number of articles on using hair for the Gulf oil spill, this isn't a new idea. It's been brought up every time there's been a spill. In the Internet era, that means starting with the Exxon Valdez and an Alabaman hairdresser inspired by pictures of oil-drenched Alaskan otters. The enterprising hairdresser thought, "if otters get this stuff on their fur so easily, shouldn't it stick to any hair?" He even named his company Ottimat.com in honor of the otter. The company's website has a video showing how the product works - it works pretty darn good. They claim that 98% of the oil adsorbed can be recovered.
The problem is that we're talking about billions of quarts of oil. That doesn't dissuade people who figure that every quart of oil recovered is one less that has to be dispersed. All across the Gulf Coast, grassroots organizations are getting people together to stuff old nylons with leftover human hair. Ironically, Matter of Trust, a nonprofit in San Francisco that specialized in making and distributing human hair mats for oil adsorption, got nailed by the recession. The companies that had been turning the hair into mats went out of business and the organization couldn't find others that would do the job for a low enough price. The woman running the organization has 18,000 lbs of hair just waiting for to be used.
The brown pelicans, sea turtles and fish in the Gulf don't really care whether the oil is adsorbed or absorbed. They just want it out of there. And so do we. Talk about hair power.