Key concepts
Physics
Surfaces
Surface tension
Hydrophilic
Hydrophobic

Introduction
Have you ever tried to catch a bubble without popping it? It’s hard! What materials can you use to successfully catch a bubble? Do some materials work better than others? Try this project to find out.

Background
Bubbles are fun and beautiful—but also fragile! A bubble is made from a thin film of soapy water with air inside. Many different things, such as contact with a solid surface, can cause the film to break, popping the bubble. But it can even pop without touching anything because the water in it gradually evaporates, making the film weaker. Sometimes, however, you might notice a bubble can land without popping.

Whether a bubble pops when it comes in contact with a solid surface depends on many different factors, including the surface properties of the material. You probably know different materials have different properties, some of which you can see or feel (such as color or density). Materials, however, have other characteristics that are harder to observe directly. Surfaces can be hydrophobic (repel water) or hydrophilic (attract water). You can observe this by dropping water onto a surface and seeing whether it forms big beads (hydrophobic) or spreads out in thin sheets (hydrophilic). Whether a material is hydrophobic or hydrophilic depends strongly on its surface roughness. Some materials, such as sandpaper, have macroscopic surface features, meaning you can feel the bumps and see them with your naked eye. Other materials, however, have microscopic ones. Even if the material looks and feels smooth to you, it might have very tiny bumps or pores. These can actually help the material repel water because the latter is held together by surface tension, and thereby unable to penetrate into the tiny gaps in the material. Other materials such as paper or sponges have larger gaps that help then absorb water.

All of these properties, along with other factors such as how fast the bubble is moving and whether the surface is wet, can affect whether a bubble is more likely to pop when it lands on a particular surface. Try this project to find out what works best to catch a bubble!

Materials

  • Bubble solution (You can buy some or make your own at home with preferably distilled water, dish soap and glycerin or corn syrup.) (see “Preparation”)
  • Small bowl or container to hold your bubble solution if you make your own
  • Bubble wand
  • Different materials to test such as aluminum foil; wax paper; printer paper; plastic wrap; wood; plastic bags or food storage containers; metal pots and pans; tables; countertops; etcetera (You can try any material you find around your house that can get soapy water on it! Note: You might not want to do this activity with certain materials such as wood or furniture because water could damage them. Check with an adult if you aren't sure.)
  • Tap water
  • Paper towels
  • Tape (optional)


Preparation

  • To make your own bubble solution, mix one cup of water with two tablespoons of dish soap and one tablespoon of glycerin or corn syrup.
  • Cut sheets of and gather the different materials you want to test. Lay them out on a flat surface, preferably indoors. (It will be difficult to do this project outdoors on a windy day.)


Procedure

  • Dip your bubble wand in your bubble solution and gently blow some bubbles toward your first sheet of material. Try to get them to land on it and not go past it. This may take some practice, so try it a few times. What happens when the bubbles hit the surface?
  • Try blowing bubbles onto each of your other materials. Do the bubbles land on any of them without popping?
  • Wet a paper towel; use it to wipe a thin layer of water onto each surface.
  • Try blowing bubbles onto each surface again. What happens now?
  • Dip a new paper towel into your bubble solution; wipe a thin layer of it onto each test surface.
  • Blow bubbles onto each surface again. Do the bubbles stick to any surfaces where they previously popped? Do they last longer after they land?
  • Extra: Does the orientation of the surface matter? Try using some tape to put your materials on a wall or even on the ceiling (checking for permission first before taping onto any surface). Can you still get bubbles to land on them?
  • Extra: Try different recipes for a homemade bubble solution. (see “More to explore”) Which bubbles are easiest to catch?

Observations and results
When all your materials were dry, you probably found smooth, waterproof surfaces did the best job catching bubbles. Wax paper, plastic wrap and aluminum foil all work well. Materials that absorb water, such as paper, probably caused the bubbles to pop because they quickly soaked up the water in the bubble. You might have been surprised to find other seemingly smooth, waterproof surfaces, such as a plastic container or a steel frying pan, also couldn’t catch the bubbles without popping them. Remember that even if these materials seem similar to you (for example, an aluminum pan and a steel pan might look very similar and both feel smooth), they might have microscopic differences in their surfaces you can’t see—and they are made from different molecules that may be more or less hydrophilic (attracted to water). You might have been even more surprised to find some rough or absorbent surfaces such as carpet could also catch the bubbles. Carpet is composed of lots of individual tiny fibers. When a bubble lands on the carpet it touches many of these tiny fibers at once, so they can hold the bubble up without popping it as a single fiber would.

When you got the surfaces wet, especially with soapy water, it should have become much easier to catch the bubbles. The water forms a thin film on top of the solid surface, preventing the bubble from touching the solid directly. This can greatly extend its life.

Cleanup
Use a damp paper towel to wipe soap residue off any surfaces.

More to explore
Bubble-ology, from Science Buddies
Blow the Best Bubbles, from Scientific American
Build the Best Big-Bubble Wand, from Scientific American
Science Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies