Reports from the Heart of the Machine
Editor: Qian Zhang
Compared with the short beauty of a normal bubble for 1 minute, the life of this bubble is extended by 200,000 times.
More than a decade ago, science fiction writer Liu Cixin wrote an interesting little story.
The protagonist of the story is a little girl named Yuanyuan, whose parents have dedicated their entire youth to improving the ecological environment of the Great Northwest, but due to the high cost of water supply, the city they have worked so hard to build, the Silk Road City, is still unable to escape the fate of abandonment.
Yuanyuan's own dream is relatively simple, she just wants to blow out a big bubble. In this regard, yuanyuan's father is worried, because he thinks that his daughter is pursuing something beautiful, novel and illusory. Growing up, Yuanyuan used what she learned to create a company with hundreds of millions of assets, but her dream is still to blow bubbles. To this end, she devotes herself to the study of bubble-related technologies, such as the development and modulation of new solutions.
Eventually, she used technical means to blow out a large bubble that could envelop a city, and let the people in the bubble punch and kick, and the bubble would not burst. Seeing this scene, Yuanyuan's father had a clever move and proposed that countless such bubbles could be wrapped to moisten the air into the Great Northwest and save a water-scarce city like Silk Road City. This idea was put into practice, and it soon began to rain lightly in the city of Silk Road...
After reading this story, some netizens said that this seems to be one of the more reliable ones in Da Liu's many brain holes, is there anyone really studying this thing?
If "this thing" refers to bubbles, of course there are, and some researchers have already made some breakthroughs.
In a recent study in the journal Physical Review Fluids, we found that physicists in France successfully used plastic particles, glycerin and water to create bubbles that lasted for as long as 465 days.
Thesis link: https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.7.L011601
Comparison of the lifespans of the three types of bubbles. a. Soap bubble: 1 minute: b. Water bubbles: 6-9 minutes; c. Water / glycerin bubble: 101 + days.
Scientists have long been very interested in bubbles.
In 2016, French physicists proposed a theoretical model to describe the exact mechanism by which soap bubbles form when jet streams hit soap films. The researchers found that bubbles only form above a certain speed, which in turn depends on the width of the airflow.
In 2018, mathematicians at NYU's Laboratory of Applied Mathematics fine-tuned the method of blowing out the perfect bubble based on a series of experiments with thin soap films. They concluded that it was best to blow bubbles with a round tube with a circumference of 1.5 inches (3.8 cm) and gently blow at a constant speed of 2.7 inches per second (6.9 cm/s). If the speed is too fast or the round tube is too thick / too thin, the bubble will burst.
In 2020, physicists determined that a key factor in creating giant bubbles is mixing polymers of different strand lengths. This creates a soap film that stretches thin enough to form a giant bubble without breaking. Polymer strands are entangled like a hair mass, forming longer strands that are not easily separated. In the right combination, the polymer can make the soap film reach a "sweet spot" that is both viscous and elastic — just not too elastic, or it will crack. Changing the length of the polymer allows for a stronger soap film.
In addition to size, scientists are also very interested in extending the life of bubbles. Bubbles take on the shape of a sphere in their natural state, a geometry that can be attributed to surface tension (a force produced by molecular attraction). The larger the surface area, the more energy is required to maintain a given shape, which is why the bubble takes on the shape of the smallest surface area: a sphere.
However, most bubbles burst within minutes of being in a standard atmosphere. Over time, the liquid flows downward under the action of gravity, while the liquid components slowly evaporate, the "wall" of the bubble becomes thinner and thinner, and the small bubbles in the bubble combine into larger bubbles. The combination of these two effects is called "coarsening." The addition of a certain surfactant strengthens the film wall, preventing surface tension from tearing the bubble apart. But eventually, the bubble will burst.
In 2017, French physicists discovered that a spherical shell made of plastic microspheres could store pressurized gas in tiny volumes. Physicists call such objects "gas marbles." These gas marbles are associated with so-called liquid marbles, which are droplets coated with tiny, liquid-repelling beads that roll on solid surfaces without cracking. Although the mechanical properties of gas marbles have been the subject of several studies, no one has yet conducted experiments to explore the lifespan of such marbles.
So Aymeric Roux and several of his colleagues at the University of Lille in France decided to fill the gap. They experimented with three different bubbles: standard soap bubbles, gas marbles made with water, and gas marbles made with water and glycerin.
To make their gas marbles, Roux et al. scattered plastic particles on the surface of the water bath, which were squeezed together to form a particle raft. The researchers then injected a little air from just below the pellet raft with a syringe to form bubbles and pushed the bubbles onto the raft with a spoon until the entire surface of each bubble was coated with plastic particles.
As expected, the standard soap bubbles burst in a minute or so. But Roux et al. found that the plastic particle coating significantly slowed the drainage of water-based gas marbles, which collapsed between 6 and 60 minutes. To further extend the life of the bubble, the researchers also need to slow down the evaporation process.
So, they added glycerin to the water. The authors say that glycerol has a high concentration of hydroxyl groups, which in turn have a strong affinity with water molecules, producing strong hydrogen bonds. So glycerin is more able to absorb moisture from the air, thus compensating for evaporation. Water/glycerol gas marbles last much longer: from 5 weeks to 465 days, which allows researchers to determine the optimal ratio of water to glycerol — the perfect recipe for "longevity" gas marbles.
In addition, researchers can not only create round bubbles, but also create strong composite liquid films, and shape metal frames into different shapes by immersing metal frames under the surface of the liquid covered with a dense layer of plastic particles. When the metal frame is slowly lifted back to the surface, the frame captures the film wrapped in particles. Most notably, Roux et al. were able to build a 3D cone with a water/glycerol liquid film, which has been around for more than 300 days (not yet broken).
The life of the liquid membrane attached to the metal frame. Left: horizontal frame; right: cone frame.
Reference links: https://arstechnica.com/science/2022/01/physicists-have-created-everlasting-bubbles/