NASA astronaut Don Pettit experiments with candy corn aboard the International Space Station to demonstrate the hydrophilic and hydrophobic properties of soap. From NPR's Science Friday, April 10, 2009. Hosted by Ira Flatow.
So how does soap work? And just what is Dr. Don Pettit saying?
First, let's think about what happens when we get dirty. Our bodies secrete oil, through sebaceous glands, to keep our skin soft and supple. Dirt clings to this film of oil.
What happens when we try to wash ourselves without soap? The same thing that happens when you try washing an oily frying pan without any dishwashing detergent. The oil repels the water, making it nearly impossible to clean.
This is because oil and water are immiscible—they do not mix. What you need is an emulsifier or surfactant, something to get the party going so that oil and water can get along.
Along comes Mr. Soap, the life of the party. Each molecule has an end that is hydrophilic (water-loving), and an end that is hydrophobic (water resistant).
One molecule of soap can't do very much...but if you have enough of them, their hydrophobic ends surround the glob of fat, creating a tidy droplet called a micelle. With the fat enclosed, and with the hydrophilic ends exposed on the surface, they're ready to rock and roll in water.
These micelle allow the oil to mix with water in a suspension or emulsion...and voila! Now the oil and grime can be washed away.
Hey...doesn't that micelle look like Dr. Pettit's ball of candy corn? Except Dr. Pettit's ball is reversed, with the water on the inside and the hydrophobic, oil-dipped ends of the candy on the outside.
Another example of an emulsion, where two unmixable substances are combined, is mayonnaise. Instead of soap (that would taste horrible!), the lecithin in egg yolks acts as an emulsifier, suspending the oil in vinegar and lemon juice.
Here's an article on how mayonnaise works: http://recipes.howstuffworks.com/question617.htm
and an easy experiment that demonstrates how soap acts as an emulsifier or surfactant:
http://candleandsoap.about.com/od/soapmakingbasics/ss/howsoapcleans.htm
©2009 Tammy Yee
So how does soap work? And just what is Dr. Don Pettit saying?
First, let's think about what happens when we get dirty. Our bodies secrete oil, through sebaceous glands, to keep our skin soft and supple. Dirt clings to this film of oil. What happens when we try to wash ourselves without soap? The same thing that happens when you try washing an oily frying pan without any dishwashing detergent. The oil repels the water, making it nearly impossible to clean.
This is because oil and water are immiscible—they do not mix. What you need is an emulsifier or surfactant, something to get the party going so that oil and water can get along.
Along comes Mr. Soap, the life of the party. Each molecule has an end that is hydrophilic (water-loving), and an end that is hydrophobic (water resistant).
One molecule of soap can't do very much...but if you have enough of them, their hydrophobic ends surround the glob of fat, creating a tidy droplet called a micelle. With the fat enclosed, and with the hydrophilic ends exposed on the surface, they're ready to rock and roll in water.
These micelle allow the oil to mix with water in a suspension or emulsion...and voila! Now the oil and grime can be washed away.
Hey...doesn't that micelle look like Dr. Pettit's ball of candy corn? Except Dr. Pettit's ball is reversed, with the water on the inside and the hydrophobic, oil-dipped ends of the candy on the outside.
Another example of an emulsion, where two unmixable substances are combined, is mayonnaise. Instead of soap (that would taste horrible!), the lecithin in egg yolks acts as an emulsifier, suspending the oil in vinegar and lemon juice.
Here's an article on how mayonnaise works: http://recipes.howstuffworks.com/question617.htm
and an easy experiment that demonstrates how soap acts as an emulsifier or surfactant:
http://candleandsoap.about.com/od/soapmakingbasics/ss/howsoapcleans.htm
©2009 Tammy Yee
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