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April 28, 2003
Volume 81, Number 17
CENEAR 81 17 pp. 34
ISSN 0009-2347



The simple interaction between soap and water molecules leads to bubble formation


BUBBLEOLOGY Bubbles form easily with the right mix of soap and water.
As a child, I whiled away boring summer afternoons entertaining our dog with bubbles. I would make them as large as possible; he would eat as many as possible. As an adult, I have learned that there is no better babysitting tool than a bottle of Mr. Bubbles. So what exactly is this stuff that fascinates children, adults, and even pets?

A soap bubble is a spherical layer of soap film encapsulating air or gas. The film consists of a thin sheet of water sandwiched between two layers of soap molecules. One end of each soap molecule is hydrophilic, or attracted to water. The other end consists of a hydrophobic hydrocarbon chain that tends to avoid water. The hydrophobic ends of the soap molecules crowd to the surface, trying to avoid the water, and stick out away from the layer of water molecules. As a result, water molecules separate from each other. The increased distance between the water molecules causes a decrease in surface tension, enabling bubbles to form.

Bubbles take their familiar spherical shape in order to minimize the energy of the soap film. A sphere provides the minimal surface area needed to enclose a given volume, making it the most efficient shape for a bubble. Even bubbles blown from odd-shaped wands end up in spheres.

The perfect soap film for bubbles comes from the perfect solution. Numerous variations of soap bubble solutions appear on the Internet. Almost all recipes involve liquid detergents, such as Joy or Dawn, and water. Unlike soaps, detergents don't contain a carboxylate group that reacts with calcium and magnesium ions found in hard water to produce a scum. Therefore, detergents aren't dependent on distilled water for bubble formation.

Glycerin--C3H5(OH)3, which can be bought in drugstores--is often included as well. Bubbles eventually burst once the layer of water evaporates, but adding glycerin lengthens the life span of bubbles. Glycerin forms weak hydrogen bonds with water, delaying evaporation. Dry air or dry hands can still burst a bubble, however.

Toronto-based Spin Master Toys' Catch-A-Bubble takes bubble strengthening to extremes. Invented by Taiwanese bubble solution expert Jackie Lin, the top-secret Catch-A-Bubble solution contains a polymer that allows bubbles to resist evaporation. The polymer reacts with air to harden three to four seconds after a bubble is blown. The bubbles can then be caught with dry hands without popping. With little or no disturbance, the bubbles can last as long as 10 days.

Harold Chizick of Spin Master Toys says that children enjoy being able to handle bubbles and have developed games based on the bubbles' durability. One such game involves trying to stack as many bubbles as possible in their hands before the bubbles burst. Once the bubbles do burst, children are left with a white, water-soluble residue that they rub off their hands. They then start the game over.

Bubbles have been a form of entertainment for centuries. Painters Jean Simeon Chardin and Charles Vanloo captured scenes of children playing with soap bubbles as early as the 18th century.

In the late 19th century, soap bubbles became more popular through an advertising tool created by the London-based A. & F. Pears soap company. Andrew Pears had developed a manufacturing process that involved removing impurities from the base soap before adding perfumes. Soap refined in this way is transparent and makes longer lasting bubbles. In 1886, Pears Soap bought Sir John Everett Millais' painting "Bubbles" and incorporated a modified version into its advertising. The company requested permission from Millais to insert a transparent bar of Pears soap into the scene of a boy blowing bubbles. The artist obliged, and the painting eventually became synonymous with Pears Soap.

Up until the early 1900s, the main tool used for blowing bubbles was a clay pipe. In the 1940s, Chemtoys--which was later acquired by Tootsietoys, the purveyor of Mr. Bubbles--introduced the popular wand-in-a-cap often found in bottles of commercial bubble solutions.

Today, a myriad of bubble-generating tools, including large rings, bubble machines, and bubble lawnmowers, are available for children of all ages.

Bubble solution options are expanding as well. In addition to pop-resistant Catch-A-Bubbles, Harold Chizick of Spin Master says that soon kids will be able to play with scented Catch-A-Bubbles and edible, fruit-flavored Yummy Bubbles.

Even family pets are getting involved in the dynamic bubble market.

Happy Dog Toys, based in Tempe, Ariz., has produced the Bubble Buddy for dogs and the Bubble Kitty for cats. Both toys produce scented bubbles. Cats can chase catnip-scented bubbles while dogs have a choice of bacon, peanut butter, or barbecued chicken scents.

Neil Werde, vice president of product development at Happy Dog Toys, says that the solution used in the toys is the same solution used by Fisher-Price for its children's products. However, Happy Dog Toys adds French perfume to the mild soap solution in order to get the dog-friendly scents. The addition of concentrated catnip oil to the solution produces bubbles infused with the scent of catnip caused by the nepetalactone found in catnip to induce feline frenzy.

Bubbles may no longer be as simple as soap and water, but I still catch myself smiling when bubbles float out of the bottle of Dawn while I'm washing dishes.

Chemical & Engineering News
Copyright © 2003 American Chemical Society

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