oil spills

[nathaniel]

Why would oil stick more readily to feathers and hay, as opposed to paper towels and cotton balls?

[deleted-71447]

Hi Nathaniel,
Welcome to the Ask an Expert forums. Can you tell us more about what you are doing for your project? Are you soaking those different materials in oil to see which one will absorb the most? If so, the answer to your question will come when you look at your results. If you explain more, I'm sure we can help.
Looking forward to hearing more,
Chris

[nathaniel]

Thanks, Chris. I tested paper towels, cotton balls, timothy hay, felt, feathers, and sand to see which would absorb corn oil the best. I thought paper towels and cotton balls would work best, but the timothy hay and feathers worked the best. I didn't think the feathers and hay would work well at all because they don't seem like their fibers are very strong, but I guess they are better than I thought. Is that why they absorbed the most oil?

[deleted-71447]

Hi, I'm not sure why the feathers and hay absorbed more oil than the paper towel and cotton ball. I expect there are many different factors that could affect your results, such as the surface area of the material (including the surfaces of pores and fibers), the adhesive forces between the material and the oil, and the capillary forces that depend on the size and shape of the pores in the material. You can try internet searches for these terms and "adsorption of oil" to get more information. Hopefully the other experts can provide some additional ideas.
I hope that helps,
Chris

[MelissaB]

I can't say much about the hay, but the fact that the feather absorbed a lot of oil doesn't surprise me. If you look at a feather under a microscope, you'll find that it's mostly empty space. Thus, there's a lot of room to absorb oil.

Birds also preen themselves with special oils they use to keep their feathers from wearing away too quickly, so they might be specially adapted to hold oil. What kind of feathers did you use? I'd assume that, say, a duck feather would hold more oil than a chicken feather since the former has waterproof plumage. Speaking of waterproof plumage, cormorants don't have it. This means that they are less buoyant underwater which means they can catch fish more easily, but it also means that they have to sun themselves and dry off their feathers after each dive.

One bird you might want to learn more about is the sandgrouse, whose feathers are specially adapted to soak up water that they then carry to the chicks--these birds live in deserts where the nearest water source may be 30-40 kilometers from their nest, so it's important that they be able to transport water! You can find more information here: http://home.montereybay.com/creagrus/sandgrouse.html.

[deleted-71588]

The initial absorption of a liquid has a lot to do with the "surface tension" at the boundry between your dry material and the liquid. You might want to do a search of "What is surface tension" using answers.com. If you look at a feather or timothy hay under a 3x magnifying glass or low power microscope, not only will you see lots of surface area, you will see a very irregular surface with lots of pointy projections. Surface tension is the property of a liquid that causes it to "ball" when spilled on a non-absorbent surface. Pointed edges at the dry / liquid boundary reduce the surface tension of the liquid which reduces its ability to "ball" into droplets which makes it easer to be absorbed. Corn oil has a fairly high viscosity at room temperature (another term you might want to do a search on) which means it tends to stick to itself and create a lot of surface tension. This means that paper products that tend to have a "dusty" or "powdery" surface will act more like a squeegee than a sponge at first with liquids that have a lot of surface tension. Paper towels tend to be designed for wet strength so they have longer fibers and tighter weaves. A more interesting paper product would have been toilet paper for this experiment because of the shorter more flexible fibers. I would expect toilet paper to absorb a lot of oil if you measure it by compairing dry and wet weight.

Another example of this surface tension of oil on dusty powdery surfaces is demonstrated in mixing a cake or pancake batter. Try observing this the next time somebody makes pancakes (assuming it isn't one of those just add water premixes). There is an art to mixing liquids into flour.

Your cotton ball represents a slightly different situation. A cotton ball usually starts with a lot of air in it. If you "wet" all of the exterior surface area of the ball without squeezing out the air first, you probably trapped a lot of air inside the ball that caused a "bubble" effect. If that occurred, the oil only coated the exterior surface trapping air inside which prevented the oil from being absorbed into the core of the ball.

Sand is a highly variable material. There are some very fine grain powdery sands that stick to any surface like dust. These would act like powdery surfaces. There are also larger grain denser sands. These tend to pack very tightly and not leave a lot of room for a liquid. When you add water to these denser sands, they typically will absorb 3 to 5 times their dry weight. If your sand was even slightly wet/damp to start with, then the water in it would prevent the oil from being absorbed because water and oil don't mix.

So how are you comparing the absorption properties of the materials? Your comparision techniques might bias your result. I would suggest that comparing the ratio of wet weight to dry weight might be a fair comparison.

[nathaniel]

Thank you for the good leads. I think I understand absorption better and will look to the microscope for more clues.

Nathaniel