Vanderbilt Student Volunteers for Science

What are bubbles?  Bubbles are round pockets of air or other gases surrounded by liquids or solids.  Most bubbles are made of air surrounded by a thin film of liquid detergent, or soap.  Soap bubbles are shaped by an equilibrium between the outward air pressure and the inward surface tension of the liquid soap film.  The detergent molecules tend to line up with one end pointing inward and the other outward, making the liquid surface more stable.  The thickness of the soap film layer is due to these detergent molecules and is the same for all bubbles, big or small.  You can see different colors in bubbles because of the light diffraction through the soap film.

Bubble Facts  Bubbles are easier to blow when it is humid- even when it’s raining!  The drier and hotter the air, the faster a bubble will POP! This is because water evaporates from the soapy film.  To make bubbles, detergent is better than soap.  Bubbles can exist because the surface layer of a liquid (usually water) has a certain surface tension, which causes the layer to behave like an elastic sheet.

How Bubbles Work… -Bubbles are made of air enclosed by a thin film of soapy water= they are “minimum surfaces” -Bubbles are made of: glycerin, soap, and water Why are Bubbles Normally Spherical in Shape? -Surface tension causes bubbles to form their typical round shape -When the upper layer of soap film becomes too thin to support the bottom layer, the bubble BURSTS!!

 Soap film is very flexible and can even produce waves! But, a bubble made with a pure liquid alone is not stable and a dissolved surfactant (materials that reduce surface tension) like soap is needed to stabilize a bubble.  Soap decreases the surface tension of water to one third of that of pure water!  The soap bubble film is very thin- less than 1 millimeter! The size of this  o

More bubbles!  Soap doesn’t make bubbles stronger. Instead, it stabilizes them by an action known as the Maragoni effect.  As the soap film stretches, the surface concentration of soap decreases, which in turn causes the surface tension to increase.  Soap makes the weakest parts of the bubble stronger and keeps them from stretching further.  Soap reduces evaporation and makes the bubbles last longer!

Why can you see the different colors when you look at bubbles? -Colors often seen on the outside of bubbles are due to “interference of light”– when two different wave lengths come and join together -Light reflected on the clear filmy outside is also reflected back inside the spherical inside if the bubble -This is why bubbles SHIMMER and look different colors -Thickness of bubbles can also play a role in the reflective properties of bubbles

Demonstration  Fill a shallow bowl with water.  Place a piece of paper on top of the water and a paper clip on top of the water.  What happens?  Then, put a squirt of detergent in the water.  What happens?  The soap has reduced the surface tension of the water- this happens in bubbles!

Activities Blowing bubbles, of course! Observe colors in the soapy film. The color on top of the bubble tells you when it will POP! Watch and see how the colors change. There is a sequence of colors: green  blue  magenta  yellow  green  white  white with black spots  POP! What color was your bubble when it popped?

Activities Dip different shapes into soapy water and see how bubbles arrange themselves. 3D triangle prism

bananarectangle pumpkin

spiral hypercube diamond

dodecahedron

Soap bubbles arrange themselves in hexagons- maximum amount of air enclosed in a minimum amount of soap film. Bubbles make use of their space- there is little wasted!