Anyone who has ever blown bubbles knows that those bubbles are usually short-lived. The situation is very different for a very special bubble, designed by French researchers.

That bubble can last for months in a row. In fact, the researchers witnessed that one of the bubbles even remained intact for more than a year – 465 days. That can be read in the magazine Physical Review Fluids†

The causes of death from a bubble
To create these long-lived bubbles, the scientists battled the three most common ‘death causes’ of a bubble. “There are three reasons why bubbles usually break,” said researcher Michael Baudoin Scientias.nl† “First of all, drainage: due to gravity, the liquid membrane at the top of the bubble becomes thinner and thinner (the liquid flows downwards) and therefore the bubble there becomes very sensitive to disturbance (for example due to vibration or dust).” In addition, evaporation is also a problem. “The liquid in the liquid membrane can also evaporate, which also leads to a decrease in the thickness of the membrane and can cause the membrane to tear.” And finally, there is also danger from outside. “When a speck of dust hits the bubble or the bubble hits a surface, that contact can cause the bubble to rupture.”

Experiment

To extend the life of a bubble, those three problems had to be overcome. To this end, the researchers created air bubbles whose membrane consisted of a mix of plastic particles, water and glycerol (a colorless sugar alcohol). Previous research had shown that such bubbles were very sturdy – you can even roll them over your hand without them popping. But the longevity of the bubbles had not yet been investigated. The researchers created several of these bubbles and monitored them using cameras. They did the same – for comparison – with ‘normal’ soap bubbles.

The ‘normal’ soap bubbles only lasted a few minutes. But the bubbles made up of a mixture of glycerol, water and plastic particles fared significantly better. Especially if the concentration of glycerol was quite high; then the bubbles lasted for months in a row and the record holder even 465 days.

Statement

The long service life can be explained by the fact that the mixture of water, glycerol and plastic particles does away with the processes that normally make an air bubble vulnerable. “The drainage is prevented by the presence of the plastic particles,” explains Baudoin. “These particles attract the liquid that makes up the membrane.” The result of this attraction is that bridges of liquid form between the particles, also called capillary bridges, which prevent the liquid from sliding down under the influence of gravity.

A long-lived bubble. Image: Michael Baudoin.

“The evaporation is prevented by adding glycerol to the water,” continues Baudoin. “Glycerol is a liquid with a strong affinity for water. It absorbs the water molecules that are in the air and thus compensates for the evaporation of water. And finally, because the bubble – because it does not get thinner over time and the plastic particles transform its surface into a kind of ‘armor’ – is also no longer sensitive to dust particles.”

Bacteria or fungi

The result is a bubble that can last for a long time. But even the firmest bubbles clearly don’t last forever. For example, the researchers saw one of the bubbles break after 465 days. What exactly caused this bubble to become fatal is unclear, but the researchers do have ideas about it. “One hypothesis is that the bubble ruptured due to the development of life forms in the bubble, such as bacteria or fungi.” The researchers deduced that they stayed in the bubble from the fact that it discolored over time. Incidentally, the presence of micro-organisms in such a bubble is not very surprising, says Baudoin. “A mixture of water and glycerol is a suitable environment for the rapid proliferation of microorganisms.”

Any older bells?

And so it may be that long-lived bells have their own causes of death. Addressing this should theoretically lead to bubbles that last considerably longer than the current record holder. “We do think that it is possible, if we can prevent the development of life in the bubble,” Baudoin says.

Unfortunately, the research does not have direct implications for people who want to enjoy their self-blown soap bubbles a little longer. However, it can eventually lead to new liquid foams: foams consisting of gas or air bubbles surrounded by liquid, of which detergent is perhaps the best-known example. “Liquid layers or membranes are the basic building blocks of liquid foams that have many different applications and are used in, among other things, the cosmetics, food and defense industries. This research could therefore lead to new liquid foams with exceptional properties.”