Shape-shifting slime

Educational objective

To explore the properties of everyday materials and observe how they can be changed.

Shape-shifting slime

Download student activity sheet [pdf]

Key student learning

• Solids, e.g. polystyrene, can change their shape.
• Gases, e.g. the bubbles in expanded polystyrene, can be used to inflate things.
• Plastics can be remoulded.
• Plastics are useful materials.

Materials list, per student or group

• Polystyrene cup (or plate)
• 2 glass beakers
• 150-200 ml of acetone
• Water
• Spatula or stirrer
• Goggles

Practicalities

Acetone is an irritant and should not be touched by the students. Use the spatula to remove the plastic and wash it in the water to remove most of the acetone before handling it. Goggles should be worn when working with acetone.

The longer the plastic is washed for the harder it becomes. After the plastic has been in the water for a few moments students can use their hands to squash it to remove more of the acetone, making the plastic more solid and easy to mould. Don’t leave it for any longer than 5 minutes or it will become too hard to mould.

Plastic shapes can be left overnight to get really hard and then decorated with felt-tip pen before students take them home.

Discussion

• Is the polystyrene a solid, liquid or gas?
• What is the acetone doing?
• Is this change to the polystyrene reversible or irreversible? Why is that? What was the polystyrene like before it was expanded with bubbles?
• Why is plastic an important material?
• What things can we make from polystyrene?
• Why did bubbles appear as the polystyrene melted?

Transition to KS4:

• What monomers is polystyrene made from?
• What physical changes are happening in the polystyrene? Relate this to your knowledge of polymers and plastic formation.
• Is polystyrene a thermosoftening or thermosetting plastic? Explain your reasoning.

Extensions

• How can you make the polystyrene set faster?
• Can you change the colour of your shape-shifting slime?
• Why would we choose to use expanded polystyrene to make disposable cups and plates instead of the plastic you have made? What would unexpanded polystyrene tableware look like?

Objects made from polystyrene.

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Links to everyday life

Polystyrene is now being used in parts of the world as diverse as Afghanistan, Alaska and the Dominican Republic as a strong and lightweight building material. This may help people to rebuild their towns after natural disasters or war. Not only is polystyrene a great insulator, it is also resistant to water, mould and mildew and able to withstand high winds, earthquakes and heavy snow.

Plastic housing: the dawn of a new era?

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A new recycling technique has been developed to help dispose of polystyrene. This technique uses limonene, a natural vegetable oil extracted from the skins of citrus fruits, which shrinks the expanded polystyrene to one 20th of its original size. This allows polystyrene to be recycled more efficiently.

A lemon squeezer

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