Stanford University engineers have found a way to stop those cute and colorful swirls found on top of soap bubbles. The pictures they took must have looked aesthetically pleasing to the eyes but the discovery means improvements in medical treatments and food technology as well.
According to Gerald Fuller, a chemical engineering professor at Stanford and co-author of the research, their study was fueled by the curiosity of a high school intern. From there, they tried to figure out how to stop the Marangoni flows, the phenomenon that happens when molecules from low surface tension areas, called surfactants, meet those that are in high surface tension areas. When these molecules meet along the boundary of both areas, they create swirls in a soap bubble. The Marangoni effect is also present in the human body since it is filled with natural surfactants, such as the tiny air sacs found inside the lungs.
According to the researchers, they were able to stop the Marangoni flow by creating an "air bubble about 1 millimeter across under the surface of a soapy solution." Then they raised it to surface quickly and repeated the process. In each process, they were able to create a new layer of swirl outside the previous one thus stopping the movement of the previous Marangoni flow. The scientists likened the phenomenon to "freezing a crashing wave."
"The colors on the bubbles indicate the thickness of the film, so you have these valleys and hills that are in a geometrical frustrated state on a surface that itself is ephemeral," said research lead author Saad Bhamla.
The idea of studying bubbles is not a novel idea. Sir Isaac Newton used bubbles to study optics. In 1991, Pierre-Gilles de Gennes got his Nobel Prize for physics for studying soap bubbles and surfactants. Moreover, soap bubbles have been investigated to improve building design and construction as well as medical treatments.
Currently, the Fuller Research Group is working on replacements for lung surfactants which can be used in infants affected by neonatal respiratory distress syndrome, where the lungs collapse. Aside from that, the group is also studying how the Marangoni effect relates to the unwanted bubbles found in drug formulations which lessen its efficacy and the quality of beer foam.
Further details of the study called "Placing Marangoni instabilities under arrest" can be found in the Physics Review Fluids.
