Science Buddies: "Ask an Expert"

Hi,

I would love if someone could scientifically explain to me how stains (food, oil etc) stick to clothing? I have asked others how to determine the chemical bond that is created and I was told that it doesn't make one. If so, I am confused as to how stains stick and remain even after water and detergent are applied to them.

We are trying to see if we can make a science project where we remove stains from a shirt without the use of water.

This is a real challenge to us so any help or direction would be appreciated.

TIA

Hi curious123,

Others have suggested that chemical bonds don't make the stains adhere to the fibers in the fabrics and, in general, I agree. Several other intermolecular forces (besides chemical bonds) also cause matter to stick together. Most of these intermolecular forces are some variation of weak electrostatic attractions. In the case of stains, the 'stain' molecules tend to adhere to the fabric more than they adhere to water and won't rinse out.

We can visualize the cleaning of a stain as the process of introducing a local chemical environment that the 'stain' likes more than it likes the fabric-- therefore it moves from the stain to the cleaning fluid and is whisked away. That's where soap comes in: a special water-soluble molecule that also has an "oily" part that enables the soap molecules to self-assemble around "oily" stains or dirt, lifting it away into the water.

In the case of water-free cleaning, solvents besides water are used to solvate the stains. Some of the more effective solvents are stinky and hazardous and others (like supercritical CO2) are less acutely dangerous.

If you find this interesting, some key words to search for (in regard to these intermolecuar forces) include Van der Waals forces, dipole-dipole interactions, London dispersion forces, and hydrogen bonding.

-John