Abstract

Objective

In this project you will make gels out of cornstarch and water, and test if you can change the consistency of the final product by changing the ratio of ingredients.

Introduction

A gel is a mixture of solid particles suspended in a liquid. The solid particles in the gel can absorb water, causing the gel to swell and increase in volume. If you have a baby brother or sister, you can see this in action by doing a quick experiment with a diaper. Just dunk the diaper in a tub of water and watch it swell as it absorbs water. If you cut open the diaper you will see the pieces of gel that are absorbing the water.

Here are some common products that use gel materials (Huggies®, Dr. Scholl's®, and JELL-O®)

Gels are very common materials because they have so many uses around the home. Here is a list of some things around the house that are made of gel materials:

• diapers,
• JELL-O®,
• pudding,
• Dr. Scholl's® insoles,
• bike seats,
• knee pads,
• Sterno®,
• air fresheners,
• hair products,
• cold packs,
• medicine gel capsules,
• toys.

Not only are gels useful around the home, they have found many uses in science, medicine, and technology. Biogels are being studied that can be used in the body for repair or to deliver medicines. Aerogels have been used to collect star dust from a comet in space. Gels have even been designed to clean up radioactive contamination!

In this experiment, you will learn how to make a simple gel out of corn starch and water. You will vary the amount of corn starch in the gel from 5% to 20% to see if this will change the properties of the gel.

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• gel
• gelatinization
• suspension
• mixture
• starch

• How are gels made and what are they made out of?
• How does gelatinization change the physical properties of a suspension?
• How does changing the ratio of ingredients change the consistency of the gel?

Bibliography

• Read about how one type of gel called aerogel was sent up into space to collect stardust:
  Ramsayer, K., 2006. "Capturing the Stuff of Space," Science News for Kids. [accessed July 3, 2006]
  http://www.sciencenewsforkids.org/articles/20060215/Feature1.asp
• Read this article and find out a gel made of polyacrylates, a family of polymers also used in disposable diapers, can help clean up sites contaminated with radiation:
  Weiss, P., 2005. "Ghost Town Busters," Science News Online. [accessed July 3, 2006]
  http://www.sciencenews.org/articles/20051029/bob9.asp
• Here is a good resource for kids that explains what materials science is all about:
  Staff, 2006. "Strange Matter: What is Materials Science?" Ontario Science Centre. [accessed July 3, 2006]
  http://www.strangematterexhibit.com/whatis.html

Materials and Equipment

• corn starch
• water
• measuring spoons and cups
• stir sticks
• small microwave-safe bowls
• permanent marker
• microwave oven
• cookie sheet lined with wax paper
• graph paper

Experimental Procedure

1. You will be making several suspensions of corn starch in water, each at a different concentration. Each suspension will have a different percentage of cornstarch (5%, 10%, 15%, and 20%) suspended in water.
2. Label each bowl with the percentage of starch (5%, 10%, 15%, and 20%) using a permanent marker.
3. Mix the ingredients for each mixture following this table as a guideline:

   	5%	10%	15%	20%
   cornstarch	5 mL (1 tsp)	10 mL (2 tsp)	15 mL (3 tsp)	20 mL (4 tsp)
   water	95 mL	90 mL	85 mL	80 mL

4. Safety note: As you heat the gel it can become super-heated and cause a burn. Take caution when stirring.

   Heat each bowl separately in the microwave on high for a total of 1 minute 30 seconds by following these steps:

   1. Stir each bowl thoroughly
   2. heat for 30 seconds
   3. stir again
   4. heat for 30 seconds
   5. stir again
   6. heat for 30 seconds
   7. stir thoroughly
5. When you heat each suspension, make observations before and after heating. Does anything change? Write down your observations in a data table:

   	Before Heating	After Heating	After Cooling	Number of Squares Covered
   5%
   10%
   15%
   20%

6. Allow the suspensions to cool to room temperature before touching them, they will be VERY HOT! As they cool, do you notice any more changes?
7. When the suspensions have cooled to room temperature, touch them with your fingers. Write down your observations in a data table.
8. Now you will measure the thickness, or viscosity, of the gels using the "ooze" method. Line a cookie sheet with graph paper and a layer of wax paper on top. You should be able to see the graph paper through the wax paper.
9. You will gently place the gel suspension, one at a time, onto the wax paper and allow the gel to spread out. Each suspension you made has the same volume, 100 mL, so if they have the same viscosity they should spread out and cover the same amount of space. It is important to leave the tray undisturbed during this test so that the gel will flatten out all by itself, and not because you are wiggling it around.
10. After the gel stops spreading, trace around it with the permanent marker and put it back in the bowl. Count the number of squares that are inside the trace and write the number in the data table. The more squares you count mean that the gel has spread out over a large space, which means it is not very thick. The fewer squares you count mean that the gel did not spread out over a large space, and so it is very thick and viscous.
11. Make a graph and compare your results. What happens to the viscosity of the gel as the amount of cornstarch is increased?

Variations

• Starches can come from many different sources, like corn, potatoes, rice, and tapioca. In this experiment you used corn starch. You can try this experiment with other kinds of starches. Will you get similar results?
• Gels can be made out of many different materials. Make gels out of different materials and devise a way to measure and compare them. Try using gelatin, agar, diaper filling, tapioca, seaweed, or fruit pectin. How do they differ and how are they similar?
• Before you heated the cornstarch, it was a suspension of cornstarch in water that was very thin and runny because it had not gelled yet. If you increase the amount of cornstarch, you could thicken the suspension and make Oobleck, a non-Newtonian fluid called a colloid. See the Science Buddies project Getting Critical Over Colloids to investigate the physical properties of this fun material.

• For more science project ideas in this area of science, see Materials Science Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies