When you think of bubbles, you realize they’re everywhere: in the dishwasher, on your beer, on the crests of the waves, in the saliva between your teeth, and of course, in bubble toys.
This means that the physics of bubbles are important in all sorts of scenarios. With this in mind, researchers at Université Paris-Saclay in France have made an intriguing discovery about the film that surrounds bubbles.
This film can be as much as 8 °C (14.4 °F) cooler than the surrounding area in some cases, the researchers say. The knowledge builds on that previous investigations how temperature changes can trigger the thinning and evaporation of a liquid film.
“Although this effect is often considered in droplet evaporation studies, to our knowledge, the importance of cold-induced evaporation is not mentioned in the soap film and foam literature,” the researchers write in their published paper.
To take a closer look at these soapy films and suds — essentially bubbles — the team created a mixture of dish soap, water, and water glycerinwith variations in the final substance used to fine-tune the lifespan and evaporation rate of the bubbles.
These bladders were tested under various temperature and humidity conditions. In some cases, the difference between the soap film and the ambient air was significant – at a maximum of 8 °C.
While it was already known that soap films lose liquid through evaporation to release energy (just like we do when we sweat to cool ourselves), it was assumed that the temperature of these films corresponded to the environment.
“Experimentally, we have observed that the temperature first falls and then rises again until the ambient temperature is reached again,” write the researchers.
“We have reported that the magnitude of the cooling effect depends on both relative humidity and initial glycerol concentration, with decreasing values of these two parameters leading to larger effects.”
One of the ways this research could be useful is in industrial processes where managing the stability of bubbles is crucial. Temperature variations between bubble wrap and the outside world affect these calculations.
The researchers say that the viscosity and surface tension of soap films are two of the properties likely to be affected by the temperature difference found; in fact, soapy objects may not have a uniform thermal field everywhere.
However, this is the first study of its kind, and much more research is needed before scientists can tell how to affect the temperature of the film that makes up a bubble.
“We propose a model describing the temperature drop of soap films after their formation that is in quantitative agreement with our experiments,” write the researchers.
“We emphasize that this cooling effect is significant and must be carefully considered in future studies on soap film dynamics.”
The research was published in Physical Verification Letters.
