Pretty Bubbles

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.  Soap bubbles seem simple, but they illustrate the mathematical problem of minimal surface, assuming the shape with the least possible surface area to contain a given volume.  The 19th century Belgian physicist Joseph Plateau described the structure of soap films and found that they obeyed certain laws, and they have a property called surface tension, which tends to minimize the surface area of the soap film.  Soap is made of pin-shaped molecules, and each soap bubble has a hydrophilic head, meaning it is attracted to water, and a hydrophobic hydrocarbon tail, 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.  Soap and water molecules assemble themselves into little bubbles called micelles, with heads pointing outward and tails tucked inside.

Inside the soap film, the air pressure is slightly higher than the pressure outside.  This pressure difference keeps the film stretched and stable.  A bubble is a closed soap film, due to the difference in outside and inside pressure, a bubble’s surface has a constant mean curvature.  Bubbles demonstrate concepts such as flexibility, color formation, reflective or mirrored surfaces, concave and convex surfaces, transparency, various shapes, elastic properties, and comparative sizing.  Soap bubbles interact with light giving them a rainbow-like appearance.  Light is made of different colors, and each color behaves differently when it meets the bubble.  Light is diffracted like a wave, leading to the interference of several waves that are superposed, generating off both surfaces of soap bubbles as they interfere with one another.  The colors you see depend on the viewing direction and angle, as well as on the film thickness of the soap bubble.

Written for Melissa’s Flash Fiction Challenge #267.