Observations and results
Before microwaving, was the 20 percent cornstarch solution less opaque, whiter and harder to stir than the 5 percent solution? After microwaving, did both solutions turn clear? Did the 20 percent solution become much thicker than the 5 percent solution? After it cooled, did the 20 percent solution spread out a lot less than the 5 percent one?
Cornstarch is made up of many molecules of glucose, specifically amylopectin and amylase. When starch is heated with water, the starch granules swell and burst, causing them to break down and release the glucose molecules into the water. Consequently, the starch molecules interact with more water, increasing the randomness of the solution. This process is known as gelatinization. When the heated solution of cornstarch and water cools down, the amylase molecules can bind each other again to create a molecular mesh. The more amylase molecules there are, the firmer, or more viscous, the mesh will be. After heating, a solution with more starch in it, such as the 20 percent cornstarch solution compared with the 5 percent one, will be firmer and stickier. Because it is more viscous, the 20 percent solution will spread out much less than the 5 percent one once cooled. Different gels can be made using different starches because starches' consistencies vary with the proportions of amylase and amylopectin that comprise them.
What could you use your gels for?
Cornstarch and water also gain interesting properties when they're mixed at room temperature. Try the activity "It's a Solid… It's a Liquid… It's Oobleck!" to have more science fun with these simple ingredients.
Solutions with cornstarch can be very sticky and messy. The 20 percent cornstarch gel should be composted or thrown in the trash. The 5 percent solution can be thrown away or diluted with water and rinsed down the drain.
More to explore
"The Page That Dripped Slime" from Bizarre Stuff You Can Make in Your Kitchen
"Water Structure and Science," from Martin Chaplin at London South Bank University
"How Play-Doh Modeling Compound Works: Starch Chemistry," from HowStuffWorks, Inc.
"Are You Gellin'?" from Science Buddies
"It's a Solid… It's a Liquid… It's Oobleck!" from Scientific American
This activity brought to you in partnership with Science Buddies