This weekend, if you have some milk in the fridge then you are well on your way to investigating polymers and surface tension. The following are 2 science experiments involving milk to try. Have fun and let me know your results!
Making Plastic from Milk
You'll need some milk and white vinegar, plus something to heat your mixture. The stove or microwave will work! Heat 1 cup of milk until it is steaming (if you use the microwave be sure to watch it carefully!). Put 4 teaspoons of vinegar into a mug. Once your milk is ready, add it to the mug. Stir the milk and vinegar slowly. What happens?
You'll see clumps, or curds beginning to form. Once there are many curds, allow the mixture to cool for a while. When it is cool enough to handle drain the extra liquid off of the curds and then put them on some paper towels. Be sure these towels are on a tray or a surface that you don't mind getting wet. Press the paper towel down on the curds to continue to soak up extra liquid. Knead the curds into a ball of dough- voila! milk plastic! If you want to make something out of your plastic, you should form it within an hour of mixing up your curds. Add food coloring or glitter to the wet dough, shape it and allow it to dry. Dried plastic can also be decorated with paint or markers.
So what happened here? Plastics are all made up of chains of repeating molecules, or polymers. Plastic can be made of chains of the same molecules or different ones. The milk you used in your experiment contains many molecules of casein protein. The vinegar is an acid and when you added it to your milk it helped the casein proteins unfold and reorganize themselves into a long chain- a polymer! The plastic you made is called casein plastic and was commonly used in the early 1900's through the 1940's to make many plastic items. Neat!
There are many variations of this experiment. www.sciencebuddies.org and www.sciencebob.com are just 2 great sites for science experiments like these!
Tie-Dye Milk: A Surface Tension Experiment
You'll need some milk, a shallow dish or pan, a q-tip, dish soap and food coloring. Pour enough milk to cover the bottom of your pan. Mix up about a half a cup of water and a squirt of dish soap in a different container. Drip several different drops of food coloring on the surface of the milk. Take the q-tip and dip it in the soapy water, then touch it to the surface of the milk. What happens?
Magic!? No, but still very cool. The soap on the q-tip breaks the surface tension of the milk. Surface tension is a force that holds a liquid together like a skin. When the surface tension was broken in your dish of milk, it allowed food coloring and more milk to escape from underneath the surface to the top, making a swirling motion.
If you enjoy mixing up creations like this in your kitchen check out www.kitchenpantryscientist.com for all sorts of experiments.