Paper Towels and Oil
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“Can you explain the effect now? With little prompting, students should reason that it
is again a matter of hydrogen bonding. Water molecules readily hydrogen bond to the
exposed –OH groups on the paper fibers while still hydrogen bonding to each other. Thus,
there is a sort of “leapfrogging” of water molecules climbing over one another to
hydrogen bond with more of the –OH groups in the paper and dragging others along
behind. This is the process of absorption on the molecular level.”Based on this explanation from this section, I’m not sure how to explain that paper towels also absorb hydrophobic oil? Is it not more due to the porosity and capillary action that paper towels work? But capillary action is a result of cohesion and adhesion, so the oil must be adhering somewhat to the paper towel, right?
Thanks for any explanation that you can give that can help this make sense to me so I can help it make sense to my kids!
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Thank you for your question Emily. It baffled me too. I pulled the following off the internet. I hope it helps.
2. Cellulose and Polarity:
Cellulose, the main component of paper towels, is a polymer made of sugar molecules.
These sugar molecules have polar (charged) regions.
Oil molecules are generally non-polar.
However, paper towels can still absorb oil due to the capillary action and the ability of cellulose to create a network that can trap oil molecules.
The porous structure of the paper towel allows oil molecules to penetrate and be held within the towel.
3. Adhesion and Cohesion:
Water molecules are cohesive (they stick to each other) and adhesive (they stick to other materials, like cellulose).
While oil is not as strongly attracted to cellulose as water, it is still able to be absorbed through the capillary action and the physical structure of the paper towel.
The oil molecules are trapped within the spaces of the paper towel, effectively removing the oil from the surface it was on.
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