Something strange is happening to the temperature around the newly formed bubbles

When you stop and think about bubbles, you realize they’re everywhere: in the dishwasher, on the top of your beer, on the crests of waves, in the saliva between your teeth, and of course, in bubble gun games.

This means that bubble physics is important in all kinds of scenarios. With that in mind, researchers from the University of Paris-Saclay in France have made an interesting discovery about the film surrounding bubbles.

In some cases, researchers say, this film can be up to 8 degrees Celsius (14.4 degrees Fahrenheit) cooler than the environment around it. The results build on previous investigations of how changes in temperature can lead to thinning and evaporation of the liquid film.

“Although this effect is often considered in studies devoted to droplet evaporation, to the best of our knowledge, the importance of evaporation from cooling has not been mentioned in the literature on soap films and foams,” the researchers wrote in their published paper.

To get a closer look at soap scum and foams—bubbles, basically—the team put together a mixture made of washing-up liquid, water, and glycerin, with differences in the final material used to adjust age and evaporation rate. bubbles.

These bubbles have been tested under different temperature and humidity conditions. In some cases, the difference between the soap film and the surrounding air was significant – reaching a maximum at a level of 8 degrees Celsius.

While it was already known that soap films lose liquid by evaporation in an effort to release energy (just as we do when we sweat to cool off), it has been assumed that the temperature of these films corresponds to the surrounding environment.

“Experimentally, we observed that the temperature first decreases and then increases until the ambient temperature is reached again,” the researchers wrote.

“We have reported that the magnitude of the cooling effect depends on both relative humidity and initial glycerol concentration, lowering the values ​​of these two parameters leading to stronger effects.”

One way this research could be useful is in industrial processes where managing bubble stability is vital. Temperature changes between the bubble films and the outside world will affect these calculations.

The researchers say that the viscosity and surface tension of the soap films are properties likely affected by the temperature gap they discovered; In fact, objects made of soap may not have a uniform thermal field all the way around.

This is the first study of its kind, however, and more research is needed before scientists can determine how the temperature of the film that makes up the bubble affects it.

“We propose a model that describes the decrease in temperature of soap films after formation that is quantitatively consistent with our experiments,” the researchers write.

“We stress that this cooling effect is important and should be carefully considered in future studies on the dynamics of soap films.”

Research published in Physical review letters.

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