Oct. 25, 2012 -- Asking a chemistry professor about soap can lead down a slippery slope. When W. Stephen McNeil's daughter was three years old, her repetitive "why?" led to an exposition involving molecular bonds and the origins of the word “hydrophobic.”
McNeil, an associate chemistry professor at the University of British Columbia, published the exchange with his daughter for the Science Creative Quarterly several years ago, but still finds himself explaining soap to non-experts.
"Most soaps are essentially surfactants," he said, "long molecules that have one end which interacts strongly with water -- hydrophilic -- and a chain that won’t interact with water -- hydrophobic."
These basic properties have given modern society everything from detergents to backyard bubble machines -- the work of proprietary research done in large corporate labs. But some academic researchers have used these molecules for a range of other cool sudsy tech, says McNeil, that you may never have heard about.
BIG PIC: Soapman, the Mummy Made of Soap
Not long after McNeil's fruitful discussion with his daughter, a group of chemists and physicists at Texas Tech University found a new use for soap bubbles. Led by professors Sandy Dasgupta and Walter Borst, the scientists essentially created molecule-sniffing soap.
A soap film is a thin layer of water caught between two layers of surfactant molecules, hydrophilic end pointing in and hydrophobic pointing out, McNeil explained. The group at Texas Tech explored ways to use soap bubbles to separate, detect and analyze other molecules.
In one experiment (abstract) they took a bubble with a water layer that contained hydrogen peroxide and measured its ability to conduct electricity. They exposed the bubble to sulfur dioxide, a gas that can be toxic at high concentrations and generate acid rain if it gets into the atmosphere. There was a detectable change in the conductivity.
McNeil marveled at the results. "You can detect less than one part per million of sulfur dioxide with a bubble!"
The New Year brought the news that British chemists had successfully created the world's first magnetic soap.
"The chemistry behind this one is very clever," McNeil said. In regular soap molecules, the hydrophilic and hydrophobic parts are what enable microscopic bubbles called "micelles" to form. These bubbles trap dirt and oil inside but stay soluble in water so the grime can be washed away, McNeil explained.
University of Bristol professor Julian Eastoe and his colleagues developed a special compound that formed micelles just like regular soap, except they contained iron that could be manipulated by a magnetic field. When a magnet was placed inside a beaker of this soap solution, the liquid clung to it. That discovery sparked new hope among environmentalists that the soap could be used to truly clean up intensely polluted areas.
Black Light Bubbles
Ravers got a trippy treat when Tekno Black Light Bubbles began floating around. These fluorescent bubbles come in blue and gold colors, cost about $4 per bottle and glow under a black light.
Certain molecules absorb ultraviolet light energy and re-emit lower-energy light in a visible range, McNeil explained. We can’t see the light being shone on the substance, but we can see light being emitted back so it appears to glow in the dark. The blue and gold colors come from compounds that re-emit UV light energy at different wavelengths.
All the bubble-makers had to do was dissolve a fluorescent compound into the soap solution. "[It's] straight-forward from a chemical standpoint," McNeil said. "But it's pretty cool looking."
Unfortunately, as Nic Halverson pointed out on Discovery News, these black light bubbles will leave glowing stains wherever they burst under the black light. To be fair, so do a bunch of other things at a show.
Soap Film 'Lens'
Soap film can be an unlikely tool, especially when soapy water is being shot at it. Physicists from the University of Nice-Sophia Antipolis and the French National Center for Scientific Research found that out earlier this year when they shot an extremely narrow soap-water jet at a large soap film surface.
What happened gets into some very complex fluid dynamics (abstract). The microjet and soap film interacted in different ways depending on the jet's angle. A narrow angle caused the jet to get absorbed into the soap film. However, past a certain wide angle, the jet could pass through the film without breaking it.
McNeil compared the microjet's behavior with the soap film to light passing through the surface of a lens. "The analogy is that you can use a soap film 'lens' to direct and focus a fluid spray," he said. This slick finding could have implications for more effective printing including 3-D printing and plastics manufacturing.
When an international research team debuted their Colloidal Display this year, the membrane screen made with soap was called the world’s thinnest.
"The word 'colloidal' simply means that there's some solid material suspended in the soap solution that isn’t completely dissolved, but the particles are so small you can’t see them," McNeil said. Researchers Yoichi Ochiai at the University of Tokyo, Alexis Oyama from Carnegie Mellon University, and Keisuke Toyoshima at the University of Tsukuba collaborated to create the display from a mixture that included soap and special colloids. The resulting film allows a finger to poke through without popping it.
A clear circular frame is dipped into the soap mixture to produce the display, and then images are projected onto it. The researchers used a mathematical model and ultrasonic waves to control the film and make it highly reflective, McNeil explained. The Colloidal Display, currently patent-pending, can produce 3-D images and make a projected image of Earth look like it's floating in space.
ANALYSIS: Dish Soap Helps Slide Bridge into Place