Chemical Education Today cover: Betsy True
NCW 2005: Cover Feature
Soap Films and the Joy of Bubbles by Mary E. Saecker
Soap Films A beautiful image of a vertical soap film swirls in the background of the cover. This film is made of two layers of soap molecules on either side, with a thin sheet of water sandwiched in between. The soap molecules consist of a hydrophobic hydrocarbon tail and a hydrophilic head. The hydrophobic tails of the soap molecules crowd to the surface, trying to avoid the water, resulting in the oily side pointing out and the hydrophilic head facing the watery interior. The colors observed in the soap film are a result of the interference of light with the film; layers of varying thickness produce different colors. Gravity makes the vertical film thicker at the bottom than at the top, and as the film’s thickness changes, the colors also change, forming regular bands. There exists a minimum thickness where the last color (yellow) can be seen. Thinner films appear black against a black background. Figure 1 shows a 30-second slice of the life of a vertical soap film. Celebrate the Joy of Toys: Host a Bubble Festival A bucket of soap solution, some wire, and string are the perfect starting ingredients for celebrating National Chemistry Week. Many resources on bubbles and bubble activities are available in print (1–5) and online (6). Some suggestions include formulating the best bubble solution for the strongest, longest-lasting bubbles (2) and making wands out of various materials and shapes.
Bubble Solutions Many different recipes are available for making a good batch of soap solution (6). A JCE Classroom Activity has students explore various ingredients to see which ones make the best solution (2). Bubbles burst once the layer of water evaporates. Adding glycerin (available at a pharmacy) helps to make
sturdy bubbles by forming hydrogen bonds with the water to delay evaporation. The recipe for the gigantic bubbles shown here is one gallon distilled water mixed with one cup Dawn dishwashing soap and four tablespoons of glycerin; the solution was allowed to “age” for 24 hours.
Wands Before the 1940s when Chemtoys introduced the wand-in-a-cap often found in bottles of commercial bubble solutions, a clay pipe was the main tool used for blowing bubbles. Many different items can be used for a wand. Here is a sampling:
photo: J. J. Jacobsen
photo: J. J. Jacobsen
As a celebration of this year’s National Chemistry Week theme, the cover of this issue tries to capture the joy of playing with bubbles. There is nothing quite like the kaleidoscopic rainbow of colors and wetly wild elastic behavior of soap films and bubbles for experiencing the pure joy of a “toy”.
• Shape a coat hanger into a circle and wrap cotton string around it • Make a circle with your index finger and thumb • Use a fly swatter; plastic strawberry basket; plastic cookie cutters • Use two straws and a piece of cotton string. Pull the string through the straws, tie the string in a knot, and hide the knot inside a straw • Tie a long piece of cotton string in a ring; have a group of people hold the piece of string together, dip the string into the soap solution, and pull it apart to create an enormous film • Roll a piece of paper into a cone and tape it; cut off the top and bottom parallel to each other to make a bubble horn • Lift a hula-hoop out of a small swimming pool filled with bubble solution while standing on a block in the middle of the pool…
Literature Cited (Web sites accessed Aug 2005) 1. 2. 3. 4.
Williams, K. R. J. Chem. Educ. 2002, 79, 1168–1169. JCE Editorial Staff. J. Chem. Educ. 2001, 78, 40A–40B. Sato, S. J. Chem. Educ. 1988, 65, 616. Barker, J.; Willard, C. Bubble Festival: Presenting Bubble Activities in a Learning Station Format; Great Explorations in Math & Science, University of California: Berkeley, 1999. 5. Zubrowski, B. Bubbles: A Children’s Museum Activity Book; Little, Brown, & Co.: Boston, 1979. 6. For example, see: Soap Bubbles. http://www.exploratorium.edu/ ronh/bubbles/bubbles.html; The Bubblesphere. http://www. bubbles.org; BubbleMania. http://www.bubblemania.com.
Figure 1. The three pictures show a vertical soap film as it ages over 30 seconds. (Photos by Viktor Obendrauf.)
www.JCE.DivCHED.org
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Vol. 82 No. 10 October 2005
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Journal of Chemical Education
1447
