Are You Gelling?
Have you ever wondered how gels are made? You probably have several kinds of products around your house—some that you eat—that use gels: puddings, diapers, shoe insoles, packaging, ice cream, toothpaste and many more.
A gel is a mixture of solid particles suspended in liquid. The solid particles in the gel can absorb water, causing the gel to swell and increase in volume. If you ever dunked a diaper in a tub of water, you have seen this in action; the diaper will swell as it absorbs the water, and if you cut the diaper open you will see the pieces of gel that are absorbing the water. These properties of gels make them quite useful for a variety of purposes. What are some of the things you can think of that gels can help do?
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
Gels are very common because they have so many uses—not only around the house but also in science. Around the house you might also find gels in: knee pads, JELL-O, bike seats, Sterno fuel, air fresheners, hair products, cold packs, toys and medicine gel capsules. In the medical field, bio-gels—gels that contain medicines—are being studied that can be used in the body for repair or to deliver medicines. Gels, specifically aerogels, have been used on space probes to collect star dust and return it to Earth for study. Gels have even been designed to clean up radioactive contamination.
A simple gel can be made using cornstarch and water, and varying the ratio will change its properties. Cornstarch, as its name implies, is starch derived from corn. Starch is a commonly consumed carbohydrate that is made of many bonded molecules of glucose (a type of sugar). It is made by most plants for use as an energy source. When water is added and it is heated, some of the bonds between the glucose molecules break and the starch undergoes "gelatinization," which means, you have yourself your very own, homemade gel!
Extra: Starches can come from many different sources, such as corn, potatoes, rice and tapioca. In this activity you used cornstarch, but you can try this activity with other kinds of starches. Do you get similar gels using different starches?
Extra: Gels can be made out of many different materials, such as gelatin, agar, diaper filling, tapioca, seaweed, or fruit pectin. You can try making gels out of these different materials. How are gels made from different materials different? How are they similar?
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.
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
Teisha Rowland, PhD, Science Buddies
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