Color Control

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Color Control
  • Age: 5+
  • Time: 30
  • (Setup: 5min, Activity: 20 min, Cleanup: 5 min)
  • Materials: $8
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  • what you need
    WHAT YOU NEED

    Materials:

    • 4 coffee filters (or paper towels)
    • Sharpie marker
    • Food coloring (at least 2 colors)
    • Water

    Equipment:

    • Ruler
    • Scissors
    • Small cups
  • What To Do
    WHAT TO DO
    1. Cut a 2-inch square from a coffee filter or a paper towel. Using a Sharpie marker, draw the lines shown in the diagram. Make sure to draw the boundaries dark enough to avoid color leaking issues. Cut away the shaded area to leave two tabs (A and B) on the bottom.
    2. Pour water into the cups, filling them close to the top. Add one color of food coloring to each cup, enough to make the colored water very dark (10 drops or more). If you want to try different color combinations, you are definitely welcome to do so! Swirl gently to mix.
    3. Place the coffee filter into the cups so that tab A dips into one color and tab B dips into the other. You can hold the paper device simply by hand or using a clamp (clothes pin) or tall glass to support it.
    4. Watch as the colored water moves up the filter. What happens as the path divides? Try drawing other designs and see how the flow can color them!

    Cleanup:  colored water can be poured down the drain. Throw coffee filters in the trash. Please be aware that the sharpie leaves stain on the desk, which can be cleaned up by isopropanol or alcohol.

  • What's Happening?
    WHAT’S HAPPENING?

    You may have noticed that the colored water stayed inside the lines as it moved up the strip. Different materials have different chemical properties that affect how they behave with water. Hydrophilic materials attract water, making contact and mixing easily. Hydrophobic materials repel water, beading up or separating out. In this case, the ink in the Sharpie marker is hydrophobic and repels water, so the colored water cannot cross the lines you drew. This allows you to control how the water flows and where the colors mix. Also, since paper has a porous structure, the colored water can freely flow through the pores.

  • So What?
    Photo of a circular diagram printed on paper. The diagram has eight spokes like a wheel. Clear liquid is being released from a clear dropper tube in the center of the circle. The liquid is spreading out inside the lines of the spokes, turning each spoke blue, pink, or yellow.

    Image credit: Frank Gomez/CSULA

    SO WHAT?

    This behavior is important for materials scientists because they can use the hydrophobic/hydrophilic boundary to direct fluid flow and design different mixing effects. Also, since paper is widely available and easy to use, it is an ideal material to use for building inexpensive devices. For example, chemicals can be added to the paper that can react with a certain solution when it comes into contact. This can be used for building devices such as pregnancy tests or blood glucose measuring kits. Currently, new paper-based materials are being developed to perform many kinds of medical testing which can be used at low cost in parts of the developing world or for detecting harmful environmental toxins like lead and other heavy metals

  • Scientists In Action
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    Scientists In Action

    Sometimes, going simpler is better. Experimenting with paper, liquid, and other basic materials, Frank Gomez and Alexis Basa are designing new sensors that could help save people’s lives around the world.