Make your own colourful slime and discover how a liquid can become a soft gel in seconds. Experiment with shapes and textures, then explore how seaweed-derived polymers and calcium ions can be used to design useful materials. These have applications in medicine, food and more sustainable packaging.
Have a go
At the Slime Time activity, you’ll become a polymer chemist and turn a liquid into a solid before your eyes.
Choose a coloured sodium alginate solution, then use a syringe to add it to a bath containing calcium ions. As soon as the liquid enters the bath, it starts to change, forming colourful strands, blobs and squishy shapes. Experiment with different techniques to create thin worms, droplets or larger slime structures.
Once you’ve made your slime, investigate its properties. Is it soft or firm? What happens if you leave it in the solution for longer? Can you work out where the solid layer forms and what remains trapped inside?
This is a hands-on drop-in activity where you can explore how chemists control the behaviour of materials by changing what happens at the molecular scale.
What’s going on
The slime starts as sodium alginate, a natural polymer obtained from seaweed. Polymers are long-chain molecules made from many smaller repeating units joined together. Natural polymers are found throughout the living world, including cellulose in plants, wool, silk and even DNA.
When the sodium alginate enters the calcium solution, something remarkable happens. Calcium ions begin linking neighbouring polymer chains together, creating a network that changes the material from a flowing liquid into a soft gel. The outer surface reacts first, forming a flexible skin around the remaining liquid inside. The longer the material stays in solution, the more of the polymer chains become linked and the thicker the gel becomes.
This simple experiment demonstrates how chemists can dramatically change the properties of a material by controlling its molecular structure. The same principles are used when designing materials for medicine, food, packaging and manufacturing.
Calcium alginate has a surprising range of applications. It can be used in wound dressings, where it forms a soft gel that helps support healing. It can also be used to deliver medicines, create edible capsules and form biodegradable films that could help reduce waste from some types of packaging. Bubble tea ‘popping’ spheres use similar alginate chemistry, with a thin gel layer surrounding a liquid centre.
The activity also connects to a bigger challenge in chemistry and chemical engineering. Polymers are used in countless everyday products, including paints, cosmetics, cleaning products and lubricants. Many are currently produced from materials derived from fossil fuels and can be difficult to recover once they enter waste streams. Researchers are working to develop renewable alternatives and more sustainable ways of designing, using and managing these important materials.
Slime Time explores how understanding molecular structure can help us create the next generation of useful, sustainable materials.