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Author Topic: How does washing up liquid work?  (Read 9120 times)

Offline george

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How does washing up liquid work?
« on: 28/12/2006 17:18:42 »
How do washing up liquids and other detergents work to "cut through grease"?

Incidentally, this question occurred to me after I read this wonderful "top tip" in Viz:

"Makers of Fairy Liquid. Why not dilute your washing up liquid a bit. Then you wouldn't have to spend a fortune on television advertising telling everyone how concentrated it is."


 

Offline Heliotrope

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Re: How does washing up liquid work?
« Reply #1 on: 28/12/2006 21:53:59 »
Most washing up liquids consist of molecules that have two ends.
One end loves to attach itself to water and the other end loves to attach itself to grease molecules.
So when you give the dish a bit of a scrub in water all the grease hopefully comes off with the water you use to clean it.
 

Offline anthony

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Re: How does washing up liquid work?
« Reply #2 on: 03/01/2007 11:18:46 »
The additional trick is that these molecules come in little balls a hundred millionths of a metre across called micelles. These balls have the detergent molecules with their water-loving (hydrophilic) ends on the outside - in contact with water - and their water-fearing (hydrophobic) ends on the inside. On the greasy surface these balls break apart an reform much larger, with a core of grease removed from the surface and drift off.

On a practical note, you may have noticed that after a while you start pulling the plates out and they are still greasy. This is because the detergent is all used up making those greasy balls. Add more. You'll notice there's no bubbles at this stage either. That's because bubbles need the spare detergent molecules, in this case the molecules form up into sheets, the bubbles skin, not balls. The bubbles skin has a middle full of water with the detergent molecules arranged on the surface with their hydrophobic ends out to the air.

A note for my former housemates. Effective cleaning involves hot water, detergent and friction!
 

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Re: How does washing up liquid work?
« Reply #2 on: 03/01/2007 11:18:46 »

 

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