Tikalon Blog by Dev Gualtieri

Eternal Bubbles

October 24, 2022

My high school mathematics courses were a good preparation for the advanced mathematics I needed in my later education. Fortunately, my high school science instruction was based on the PSSC, BSSC, and CHEMStudy curricula designed as the Space Race response to generate more scientists in the United States. Intermixed with these were the compulsory English language and English literature courses that likely help with my writing skills. Nothing was too memorable in those courses, except a particular sonnet.

That sonnet was Ozymandias by Percy Bysshe Shelley (1792–1822). It's a reflection on the impermanence of the works of man, in this case, those of Ramesses II (c. 1303-1213 BC), also known as Ramesses the Great and by his Greek name, Ozymandias. An unnamed traveler happens upon a ruined sculpture bearing the inscription, "King of Kings am I, Osymandias. If anyone would know how great I am and where I lie, let him surpass one of my works." This is written by Shelley, as follows.

Two vast and trunkless legs of stone
Stand in the desart. Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read.

Although we can never break the second law of thermodynamics (the entropy law), we still strive to fashion eternal things, sometimes aided by materials science. As if responding to the lesson of Ozymandias, there are sculptures made from COR-TEN steel, designed to rust to a stable patina and resist subsequent corrosion. However, despite the claim that "diamonds are forever," they will burn like any other form of carbon.

There are many eternal flames in the world, as attested by the eternal flames Wikipedia page. A prominent United States example is the John F. Kennedy Eternal Flame in Arlington National Cemetery, created to commemorate the life of John F. Kennedy (1917-1963), the 35th President of the United States. This gas flame was temporarily extinguished in August, 1967, just a few years after its initial lighting.

Right image, the eternal flame at the John F. Kennedy grave site in Arlington National Cemetery, photographed by Tim Evanson on May 30, 2013.

Left image, John F. Kennedy, public domain photograph by White House photographer, Cecil Stoughton, National Archives Identifier (NAID) 194255. Both images via Wikimedia Commons. (Click for larger image.)

One notably non-eternal object is the soap bubble, an inexpensive way to entertain children in the summer months. Soap bubbles became useful in physics in the late 1940s when Nobel laureate, William Lawrence Bragg (1890-1971), and John Nye (1923-2019) of the Cavendish Laboratory of Cambridge University produced arrays of soap bubbles floating on water, called bubble rafts, to simulate atoms in crystals.[1] I wrote about bubble rafts in two previous articles (Kirchhoff–Plateau Problem, June 15, 2017 and Soap Films, April 28, 2011.

Bragg and Nye created bubble rafts of 100,000 or more sub-millimeter bubbles. These simulated atoms allowed study of such crystal phenomenon as grain boundaries and dislocations.[1] Their bubble recipe was an aqueous solution of glycerine, oleic acid, and triethanolamine in water.[1] triethanolamine is not a common household item, although olive oil might substitute for the oleic acid. A recipe for a playtime bubble solution is 2/3 cup of dishwashing liquid and 2/3 tablespoon of glycerine (also known as glycerol) in a gallon of water. The purpose of the glycerine is to slow the evaporation of water from the bubble, thereby increasing its lifetime.

A bubble raft with bubbles that are about 1.5 millimeter in diameter from a laboratory class at MIT.

Bubble rafts are often used in physics teaching laboratories. An edge dislocation (an inserted row of bubbles) can be seen in the lower right hand quadrant.

(Wikimedia Commons image by Vlad Tarasov, modified.)

A soap bubble may persist for a minute. Why they are stable at all relates to the surface tension of water. The uniform tension at all points on the surface is responsible for pulling a bubble into its spherical shape against the internal gas pressure. The soap molecules, being hydrophilic on one end and hydrophobic on the other, form protective layers on the inside and outside of the water layer. On the outside, this reduces the evaporation of water, reduces the eventual removal of surface tension, and bursting of the bubble.

A large soap bubble reflecting a streetscape in Ljubljana, Slovenia.

Soap bubbles containing glycerine have a longer lifetime, since the glycerine molecules have a low vapor pressure, they are hydrogen-bonded to the water molecules, and they hinder the water evaporation.

(Wikimedia Commons image by P.L. Bechly.)

So, preventing water evaporation is the trick to making a bubble with a long lifetime. A team of physicists from the Université Polytechnique Hauts-de-France (Lille, France) have created Everlasting bubbles by encapsulating them in plastic microparticles.[2-4] One such water-glycerine bubble that they created had a 465 day lifetime.[3-4] This is a lifetime that's more than 200,000 times as long as that of a typical soap bubble.[3]

These gas marbles are created in a liquid solution that allows the microparticles to pack together on the bubble surface.[3] This plastic shell gives the bubbles enough strength that they can be held in a hand and rolled along a surface. Gas marbles created from water alone lasted up to an hour, but water-glycerol marbles had a much longer lifetime, with one lasting 465 days.[3] The team speculates that the glycerine absorbs water from the air, while the plastic microparticle shell prevents drainage of water from the shell.[3]

An example of a gas marble.

Principal author of this research, Michaël Baudoin, a professor at the Université Polytechnique Hauts-de-France (Lille, France), presented the French team's research at an online session of a Physical Review journal club hosted by the American Physical Society (APS) and archived at the APS YouTube Channel.[5].

(Still image from a YouTube Video.[5])

As Michaël Baudoin, a professor at the Université Polytechnique Hauts-de-France (Lille, France) and principal author of this research, explained, another research group was the first to create gas marbles, but these were much larger and hydrophobic instead of hydrophilic.[4-5] These gas marbles had a shorter lifetime, and the issue of longevity was not addressed.[4-5] Baudoin's team created their gas marbles by floating 80 micrometer plastic microparticles on a liquid surface and bubbling air from below.[4-5]

When the liquid was just water, the microparticle coated bubbles burst in about half an hour, and experiments in which the relative humidity was changed indicated that water evaporation was responsible.[4-5] Another mechanism for water loss, drainage to the bottom of the bubbles, was prevented by capillary bridging of the water between the microparticle beads.[4-5] The next step was addition of glycerine, which both retarded evaporation and pulled water from the air to maintain the surface water.[4-5] The French team also developed a model of the bubble stability.[4-5]

Eternal Bubbles

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