Super Giant Soap Bubbles

What's more fun than bubbles?  How about humongous bubbles!  Making super giant-sized soap bubbles is actually pretty easy, but it turns out there is a lot more science going on here than you probably thought.

from Soap Bubble Wiki (link below)

Click and expand the tabs below to get started

what you'll need

For Bubble Solution (1 gallon):
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• 10 tablespoons dish soap or detergent- Dawn seems to work best, try to get unscented or Professional (usually available at Sam's Club or Costco)
• 1 teaspoon Guar Gum (available at most health food stores. If you can't find Guar Gum, cornstarch is a reasonable substitute.)
• Baking powder (not baking soda)
• 3 teaspoons Rubbing (Isopropyl) alcohol
• Bucket or other container to hold about 1 gallon (a 5 gallon bucket is great if you want to make more)
• Small cup
• A small spoon or popsicle stick and a big spoon
• Measuring spoons or cups

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For each giant bubble wand:
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• 2 garden stakes or sticks, ~12" - 24" long (something with a hole or loop in one end is best so that you can tie the cord to the stakes)
• Cord or rope (soft braided cotton works best, not too thick ~1/8" to 1/4", ~8' long)
• A fairly heavy hex nut or washer(s) (with a hole your cord will fit through)
• Scissors

​For small bubble wands:
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• Drinking straws
• Cotton yarn or string

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basic procedure

Prepare bubble solution (for 1 gallon)
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1. ​Measure 1 teaspoon of guar gum in a small cup or bowl.
2. Slowly add 2-3 teaspoons of isopropyl (rubbing) alcohol while stirring to make a smooth slurry or paste.  Set aside. [If you're using cornstarch instead of guar gum you can use water instead of rubbing alcohol.]
3. Add 1 - 2 quarts of very warm water to a bucket large enough to hold at least 1 gallon.
4. While stirring the water with a large spoon, slowing add the guar gum and alcohol slurry.  Rinse the cup once or twice with water from the bucket to get all of the guar gum.
5. Let the water stand for several minutes, stirring occasionally.  You may notice the solution thicken a bit as the guar gum hydrates (absorbs water).
6. Add more water (cold is fine) to make a total of 1 gallon and stir.
7. Add 2 teaspoons baking powder and stir until dissolved.
8. Add 10 tablespoons dish soap (or 1/2 cup + 2 tablespoons), stirring gently.  Try not to make many bubbles or foam as you stir.
9. ​For best results, allow the solution to age several hours or even overnight before use.

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Assemble large bubble wand

1. Cut 2 lengths of cord or rope, 1 twice as long as the other.  For your first large wand, 18" and 36" lengths should work well.  As you gain more experience and want to make really large bubbles you can use longer cords.
2. Tie each end of the shorter cord securely to the loops of your garden stakes.
3. Thread a hex nut or a couple washers onto the longer cord, then securely tie each end to the garden stakes as you did in Step 2.  
4. Holding a garden stake by the free end in each hand (i.e. with the loop/cords on the opposite ends), separate them until the top (shorter) cord is straight and the bottom (longer) cord hangs below (due to the weight of the hex nut) forming a triangle shape.

Assemble small bubble wand

1. Cut a length of string or yarn about 4 times the length of your drinking straws.
2. Thread the string through each of the straws, then tie the ends of the string together with a small knot.
3. Holding a straw in each hand, slide them around the string to make a square window frame, with straws on the left and right sides and string on the top and bottom sides.

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making giant bubbles

1. It's much easier to make giant bubbles if there is no wind, but if there is a breeze, stand with your back to the wind.  Be prepared to turn your body if the wind changes direction.  
2. Holding the end of a wand handle in each hand, bring your hands close together so that the cords are touching and dangling straight down in a straight line.
3. Carefully dip the cords into your soap bucket, trying not to tangle them.  If the cords are dry (i.e. the first time you use your wand) you may want to let them soak in the soap solution for several seconds so they can absorb plenty of water.
4. Slowly lift your wand straight up and out of the soap solution, keeping your hands close together and the cords touching.
5. Holding your hands as high as you can, slowly open the wand completely by moving your hands apart.  If there is no wind, slowly walk backwards to create enough air flow to start blowing a bubble.
6. To release and launch your bubble so that it can float away, slowly close your wand by moving your hands close together again.
7. If your bubble pops, try again.  Making really big bubbles takes practice, but it's lots of fun while you're learning!

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what's happening

Did you know that water molecules are actually very sticky?  You've probably seen them clinging to lots of surfaces like walls, windows and tables.  When one material sticks to another we call it adhesion, and water molecules adhere or stick to many other materials, but they also like to stick to other water molecules.  When a material sticks to itself we call it cohesion.  If there is no good surface around for water to stick to it's perfectly happy sticking to itself by pulling on several other water molecules nearby.  In fact, each water molecule pulls so hard on the others around it that all of the water tries to pull itself into one tight spherical ball if it can't find anything else easier to stick to.  This force is sometimes called surface tension.  Pour some water onto a freshly waxed car or tabletop and it forms lots of little droplets or "beads" because it can't stick as well to the waxy surface (check the video link at the end to see what water does on the International Space Station).   If you pour it on most other surfaces, however, it will spread out if it can stick to those surfaces.

Okay, so what's all this have to do with soap bubbles?  A bubble is like a balloon, with a thin film or skin on the outside surrounding and trapping air (or some other gas) inside.  Water doesn't stick to air though, leaving only other water molecules for it to stick to, but the surface tension of water, or the force with which it pulls on other nearby water molecules, is so strong that it will form small beads full of water (like raindrops) rather than stretching into a thin film.  If we want to stretch water into a thin skin to make a bubble we need to add something else that it would rather stick to, and that's exactly what soap does.  Soaps and detergents are usually long snake-like molecules with one end (let's call it the head) that likes to grab or pull on water molecules while the other end (tail) likes to get as far away from water as possible (or if possible grab something very different like oil or grease, which, by the way, is what makes them so good at cleaning dirt).  

The head ends of soap molecules in your bubble solution grab onto water molecules, but since their tail ends want to get out of the water at the same time, they can only grab one side so that their tail ends can remain in the air.  Other soap molecules can also grab onto the same water molecules but from the opposite side, while also keeping their tail ends in the air.  This leaves the water molecules free to grab some other water molecules, but only in a region where there is no soap, forming a thin three-layer film skin.  You can think of these three layers sort of like a peanut butter sandwich, where the pieces of bread on the top and bottom are the soap layers and the peanut butter inside is the water.  The surface tension of the water layer inside gives the skin of your bubble its strength, while the soap layers above and below weaken the surface tension just enough to allow the water to stretch out into a thin film so that you can blow a bubble.  Materials like soap that reduce the surface tension of water (or other liquids) in this way are called surfactants.

The soap-water-soap film may be strong enough to form a skin of a bubble but it's also very, very thin- thinner than the hair on your head- so there is a limit to how big a bubble you can make with just the cohesive force of water holding it together.  Making it any bigger and the skin will break, popping the bubble.  The guar gum (or cornstarch) you added to the water gives it extra strength to make even bigger bubbles.  The baking powder also helps by controlling pH or acidity of the solution.  You may have seen some soap bubble recipes that add glycerine to the soap, which works by slowing the evaporation of water (although most bubble experts agree that recipes like ours work much better).  Reference links at the end explain in more detail how these ingredients work.  

variations and related activities

Try blowing a small bubble inside one of your big bubbles.  To do this get as close as you can to the big bubble without touching it, then gently blow a puff of air into the wall of the bubble (see the video).

Why do bubbles pop?  Remember that the skin of a soap bubble is very thin, and it's only the water layer which really holds the bubble together as the soap layers on either side actually weaken the water's cohesive forces or surface tension.  As the layer of water evaporates the skin of the bubble gets thinner and thinner until the water molecules can no longer hold onto each other and the bubble pops.  Do you think your bubbles would last longer on a hot and dry day, or a cool and humid day?

​Of course a bubble also pops when you touch it- that is if you touch it with your dry finger or something else that draws the water out of its film just like evaporation does.  If you dip your finger or hand into the soap solution you should be able to carefully push it through the skin of the bubble and pull it back out without popping it.  You can even catch and hold a bubble in your hand (as long as your hand is completely wet- touch it with any dry skin and it will pop.  

How can a triangle or square shaped bubble wand still make spherical (ball-shaped) bubbles?  Once you release your bubble from the wand you may have noticed that it quickly formed a more  spherical shape.  This is because a sphere is the most stable shape for a bubble, allowing it to enclose the most air while using the least amount of soap (mathematicians might say enclosing the maximum volume with the minimum surface area).  Huge bubbles have a large amount of water in their skins, however, and as gravity pulls on this water (as well as any wind blowing on the bubble) the relatively heavy skin gets tugged quite a bit, which is why the bubble wobbles and changes shape a bit as it moves, but it still tries to remain mostly spherical.

Did you also notice how colorful your bubbles are (look at the photo above)?   In fact, the different colors form rainbow-like stripes that circle around the bubble (although the colors here are formed in a different way than they are in a rainbow).  These colored stripes are called interference fringes and caused by light rays reflecting off the thin soap-water-soap film of the bubble.  Some light rays reflect off the outside surface of the film and back to your eyes while others pass through this surface, into the film itself, and then reflect off the inside surface and then back to your eyes.  When these various light rays recombine on the way to your eyes we say that they interfere with each other.  This also happens when light rays strike a pane of window glass, but the soap film of the bubble is much, much thinner.  In fact, the thickness of the soap film is close to the wavelengths of light, so that this interference creates colored bands as the thickness of the film changes, which is why the colors change as the bubble slowly evaporates and its skin gets thinner (check out the references at the end to learn more about the physics of light).  Gravity also pulls the water in the bubble downward, so that it's skin is thicker near the bottom.  Thus the fringes or bands of color indicate changes in film thickness similar to how the lines on a contour map indicate elevation changes.  

references and links to more information

Just about everything you ever wanted to know about soap bubbles:

• https://soapbubble.fandom.com/wiki/Soap_Bubble_Wiki
• https://www.exploratorium.edu/search/bubbles
• https://soapbubble.dk/en/articles
• https://www.popularmechanics.com/science/a30781401/bubble-math/
• https://arstechnica.com/science/2020/02/physicists-determine-the-optimal-soap-recipe-for-blowing-gigantic-bubbles/

How does soap work, and what is the difference between soap and detergent?:

• https://www.thoughtco.com/how-dos-soap-clean-606146
• https://sciencetrends.com/science-behind-soap-works-make-clean/
• https://explorationclean.org/science

Experiments and other activities with surface tension and soap:

• https://www.scienceworld.ca/resource/catch-bubble/​
• http://www.planet-science.com/categories/under-11s/chemistry-chaos/2011/06/soap---how-does-it-get-things-clean.aspx
• https://www.york.ac.uk/res/sots/activities/soapysci.htm
• https://www.teachengineering.org/lessons/view/duk_surfacetensionunit_less1
• https://www.homesciencetools.com/article/how-to-make-super-bubbles-science-project/

Surface tension of water in space:

• https://mashable.com/2015/10/13/water-blob-space/

Why are bubbles round?:

• https://www.scienceabc.com/pure-sciences/why-are-bubbles-round.html
• https://brilliant.org/wiki/math-of-soap-bubbles-and-honeycombs/

Colors in soap bubbles (and rainbows, just for fun):

• https://www.exploratorium.edu/ronh/bubbles/bubble_colors.html
• https://www.explainthatstuff.com/thin-film-interference.html
• https://micro.magnet.fsu.edu/primer/java/interference/soapbubbles/
• https://science.howstuffworks.com/nature/climate-weather/storms/rainbow2.htm
• https://en.wikipedia.org/wiki/Rainbow
• https://www.rookieparenting.com/make-your-own-rainbow-science-experiment/

Subject Tags
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• Bubbles
• Soap​​
• Water
  

Related Physics Subject Tags

    Surface Tension

All Chemistry Subject Tags

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Acid/Base Chemistry
Bubbles
Crystals
Density
Food Chemistry
Heat/Cold
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Phase/State Changes
Polymers
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