Tag Archives: Leidenfrost effect

Fluid mechanics in the kitchen

Caption: Dr. Maciej Lisicki is developing a formula for perfectly creamy ice cream in his laboratory. Credit Photo: Michal Czerepaniak, source: Faculty of Physics, University of Warsaw.

It’s unusual to see a scientist in an orange (maybe it could be called fire engine red?) jumpsuit as it has an altogether different meaning (prison wear) in the US.

Sadly, there isn’t a video of Dr. Maciej Lisicki or other scientists in the kitchen but here’s a description of what they’ve been up to from a June 22, 2023 University of Warsaw (Poland) press release (also on EurekAlert),

Take four brilliant physicists who specialize in fluid mechanics and put them in the kitchen. Give them pots, pans, basic foodstuffs, and a bottle of champagne. Add a COVID-19 pandemic, a pinch of boredom, and a handful of good ideas. Stir, wait, and voilà – you have a “delicious” publication that will teach you how bubbles are created in champagne, how to brew the perfect espresso, and how “kitchen revolutions” can contribute to innovations in many fields, including biomedicine and nanotechnology.

Most of us visit this place every day. But the kitchen is not just for cooking meals. “It can be an excellent place to conduct experiments and even make scientific discoveries,” argues Maciej Lisicki, of the Faculty of Physics of the University of Warsaw, co-author of a publication in the prestigious journal Reviews of Modern Physics. The team of researchers, which in addition to Maciej Lisicki includes Arnold Mathijssen of the University of Pennsylvania, Endre J.L. Mossige of the University of Oslo and Vivek N. Prakash of the University of Miami, not only explores the history of food science, but also shows how phenomena in the kitchen lead to innovations in biomedicine and nanotechnology.

COVID pandemic and bubbles in champagne

Maciej Lisicki and his fellow researchers began working on the article during the COVID-19 pandemic, when many researchers could not work in the lab and began experimenting in their homes. “It started primarily with the intention to make an educational tool, given that kitchens offer a low barrier of entry to doing science — all you need are some pots, pans, and a few ingredients to get a few reactions going—but it quickly grew into a more scientific reflection of the history of food once we realized how interwoven the fields are,” says Arnold Mathijssen.

The team of researchers constructed the results of their work along the lines of a menu. “Tasting” begins with the physics of drinks and cocktails, then moves on to main courses, and finishes with coffee and desserts, whose preparation is also based on the intuitive use of the laws of nature.

As with any good party, everything begins with the opening of a bottle of champagne. After a characteristic “pop”, we observe how a mist forms around the neck of the bottle. – This phenomenon is associated with a rapid change in pressure. Inside the bottle it reaches almost five atmospheres, but when the bottle is opened it drops to one atmosphere.  “The expansion is accompanied by a drop in temperature, which causes the water vapor that accumulates near the mouth of the bottle to freeze, and the carbon dioxide coming out of the bottle to condense”, Maciej Lisicki explains.

In their paper, the researchers also look at bubbles, which give sparkling wines their unique flavor. “Circulating bubbles force the transport of the liquid in the glass, and thus facilitate the release and spread of aromatic notes and flavors”, the researcher adds. From the section of the paper devoted to drinks and cocktails, we will also learn what makes the foam in beer so thick and stable, why aniseed drinks such as rakija and ouzo get cloudy when enough water is added (the phenomenon is even called the “ouzo effect”), and what “tears of wine” are.

When water surfs the pan

Moving on to the main course, the scientists explain the role of heat and its effect on food textures, aromas, and flavors. Among other things, they describe the Leidenfrost effect, in which a drop of liquid placed on a very hot surface forms an insulating layer of vapor, that prevents rapid boiling. “Water drops thrown onto the pan ‘surf’ and even bounce off the surface, instead of evaporating immediately”, Lisicki says. 

Proper temperature is crucial in the preparation of many foods. “It doesn’t take a Ph.D. in physics to fry the perfect steak. Everyone knows that one needs to quickly sear the meat in a sufficiently hot pan. As a result, the proteins on the surface of the steak coagulate and the moisture is kept inside”, the researcher explains. 

A Ph.D. in dishwashing

The text also includes examples of scientific discoveries that researchers have made without leaving their own kitchens. One of them is related to the biography of Agnes Pockels.

“Her story speaks of the inequality in science. She was a woman in Germany in the late 19th century, so she was not allowed to attend university for formal training, making it difficult for her to submit her research to journals,” Mathijssen says.

Running her parents’ household and spending a lot of time in the kitchen, she quickly began experimenting there. “Observing the formation of foam and films on the surface of dirty dishes, she was the first to describe the phenomenon of surface tension and developed an instrument to measure it. Initially, scientific journals were reluctant to publish the results of her experiments due to her lack of formal training and affiliation with university staff. Her first paper was published through Lord Rayleigh in Nature and contributed to the understanding of surface effects in liquids. Agnes Pockels then became well-known and respected, and all her subsequent work was published in high-profile journals. This example shows that it is possible to become a respected scientist without leaving home,” notes Maciej Lisicki.

Salad dressing vs. nanoengineering

Research in fluid mechanics can help improve food processing technologies, as well as find applications in other fields such as nanoengineering and medicine. “In an earlier study (“Rechargeable self-assembled droplet microswimmers driven by surface phase transitions”, published in Nature Physics) conducted by my team, we used a simple emulsion that is the basis of salad dressings – oil with water. We were able to make droplets of such an emulsion, with the addition of a surfactant, form tendrils under temperature and move like bacteria. Such nontoxic, biocompatible microfluidics could be used in the future, for example, to precisely deliver drugs anywhere in our bodies”, Lisicki explains. 

The review also highlights the applicability of these technologies in areas such as food safety and quality control. By deploying devices that can detect food-borne pathogens or toxins using principles of fluid dynamics, the scientific community can contribute significantly to public health.

Another key aspect of their review is the potential impact it could have on policy decisions, particularly those related to environmental sustainability and food safety. The authors highlight the significance of science-based policies, for example – referencing the announced EU ban on PFAS non-stick coatings by 2030. Using the scientific understanding offered by studies like these, policy makers can make informed decisions to foster a more sustainable and safer food future.

“Kitchen flows show us that significant scientific problems are available at our fingertips and do not always require space technology to explore them. On the other hand, more than a few cosmic technologies were born from inspiration by everyday phenomena. The kitchen can therefore entertain us, but also teach us – in this case, physics. This is why it is worth a try to unleash your curiosity and experiment!” Lisicki adds.

This research was supported by the United States Department of Agriculture (USDA-NIFA AFRI 2020-67017-30776 and 2020-67015-32330).

Faculty of Physics of the University of Warsaw
Physics and astronomy at the University of Warsaw appeared in 1816 as part of the then Faculty of Philosophy. In 1825, the Astronomical Observatory was established. Currently, the Faculty of Physics at the University of Warsaw consists of the following institutes: Experimental Physics, Theoretical Physics, Geophysics, the Department of Mathematical Methods and the Astronomical Observatory. The research covers almost all areas of modern physics, on scales from quantum to cosmological. The Faculty’s research and teaching staff consists of over 200 academic teachers, 88 of whom are professors. About 1,100 students and over 170 doctoral students study at the Faculty of Physics at the University of Warsaw.

Perhaps the paper provides more information about the ice cream research depicted in the visual image at the top of this posting. Here’s a link to and a citation for the paper,

Culinary fluid mechanics and other currents in food science by Arnold J. T. M. Mathijssen, Maciej Lisicki, Vivek N. Prakash, and Endre J. L. Mossige. Rev. Mod. Phys. Vol. 95, Iss. 2 — April – June 2023 025004 DOI: https://doi.org/10.1103/RevModPhys.95.025004 Published: 5 June 2023 © 2023 American Physical Society

This paper is behind a paywall.

Extreme water repellency achieved by combining nanostructured surfaces with Leidenfrost effect

Apparently a new twist has been added to the water repellency story. From a May 17, 2016 news item on ScienceDaily,

What do you get if you combine nanotextured ‘Cassie’ surfaces with the Leidenfrost effect? Highly water-repellent surfaces that show potential for developing future self-cleaning windows, windshields, exterior paints and more [sic]

Combining superhydrophobic surfaces with Leidenfrost levitation–picture a water droplet hovering over a hot surface rather than making physical contact with it–has been explored extensively for the past decade by researchers hoping to uncover the holy grail of water-repellent surfaces.

A May 17, 2016 American Institute of Physics news release on EurekAlert, which originated the news item, provides more detail about the work,

In a new twist, a group of South Korean researchers from Seoul National University and Dankook University report an anomalous water droplet-bouncing phenomenon generated by Leidenfrost levitation on nanotextured surfaces in Applied Physics Letters, from AIP Publishing.

“Wettability plays a key role in determining the equilibrium contact angles, contact angle hysteresis, and adhesion between a solid surface and liquid, as well as the retraction process of a liquid droplet impinged on the surface,” explained Doo Jin Lee, lead author, and a postdoctoral researcher in the Department of Materials and Engineering at Seoul National University.

Nonwetting surfaces tend to be created by one of two methods. “First, textured surfaces enable nonwettability because a liquid can’t penetrate into the micro- or nano-features, thanks to air entrapment between asperities on the textured materials,” Lee said.

Or, second, the Leidenfrost effect “can help produce a liquid droplet dancing on a hot surface by floating it on a cushion of its own vapor,” he added. “The vapor film between the droplet and heated surface allows the droplet to bounce off the surface–also known as the ‘dynamic Leidenfrost phenomenon.'”

Lee and colleagues developed a special “nonwetting, nanotextured surface” so they could delve into the dynamic Leidenfrost effect’s impact on the material.

“Our nanotextured surface was verified to be ‘nonwetting’ via thermodynamic analysis,” Lee elaborated. “This analytical approach shows that the water droplet isn’t likely to penetrate into the surface’s nanoholes, which is advantageous for designing nonwetting, water-repellant systems. And the water droplet bouncing was powered by the synergetic combination of the nonwetting surface–often called a ‘Cassie surface’–and the Leidenfrost effect.”

By comparing the hydrophobic surface and nanotextured surface, the group discovered that enhanced water droplet bouncing was created by the combined impact of the Leidenfrost levitation and the nonwetting Cassie state.

“A thermodynamic approach predicts the nonwettability on the nanotextured surface, and a scaling law between the capillary and vapor pressure of the droplet explains the mechanism of the dynamic Leidenfrost phenomenon,” said Lee.

These findings should “be of value for a wide range of research areas, such as the study of nonwetting surfaces by the Leidenfrost effect and nanotextured features, enhanced liquid droplet bouncing, and film boiling of liquid droplets on heated Cassie surfaces,” he added.

Significantly, the group’s work furthers the fundamental understanding of the dynamic Leidenfrost droplet levitation and droplet-bouncing phenomena on hydrophobic and nanoengineered surfaces. This means that it will be useful for developing highly water-repellant surfaces for industrial applications such as self-cleaning windows, windshields, exterior paints, anti-fouling coatings, roof tiles, and textiles in the future.

“Our future work will focus on developing multiscale structures with microscale and nanoscale regularities, and explore the nonwetting characteristics of their surfaces with the dynamic Leidenfrost effect,” Lee noted.

Here’s a link to and a citation for the paper,

Anomalous water drop bouncing on a nanotextured surface by the Leidenfrost levitation by Doo Jin Lee and Young Seok Song.  Appl. Phys. Lett. 108, 201604 (2016); http://dx.doi.org/10.1063/1.4948769

This paper appears to be open access.

Hands off the bubbles in my boiling water!

The discovery that boiling water bubbled was important to me. I’ve never really thought about it until now when researchers at Northwestern University have threatened to take my bubbles away, metaphorically speaking. From the Sept. 13, 2012 news item on ScienceDaily,

Every cook knows that boiling water bubbles, right? New research from Northwestern University turns that notion on its head.

“We manipulated what has been known for a long, long time by using the right kind of texture and chemistry to prevent bubbling during boiling,” said Neelesh A. Patankar, professor of mechanical engineering at Northwestern’s McCormick School of Engineering and Applied Science and co-author of the study.

This discovery could help reduce damage to surfaces, prevent bubbling explosions and may someday be used to enhance heat transfer equipment, reduce drag on ships and lead to anti-frost technologies.

The Sept. 13, 2012 news release from McCormick University (which originated the news item) provides details,

This phenomenon is based on the Leidenfrost effect. In 1756 the German scientist Johann Leidenfrost observed that water drops skittered on a sufficiently hot skillet, bouncing across the surface of the skillet on a vapor cushion or film of steam. The vapor film collapses as the surface falls below the Leidenfrost temperature. When the water droplet hits the surface of the skillet, at 100 degrees Celsius, boiling temperature, it bubbles.

To stabilize a Leidenfrost vapor film and prevent bubbling during boiling, Patankar collaborated with Ivan U. Vakarelski of King Abdullah University of Science and Technology, Saudi Arabia. Vakarelski led the experiments and Patankar provided the theory. The collaboration also included Derek Chan, professor of mathematics and statistics from the University of Melbourne in Australia.

In their experiments, the stabilization of the Leidenfrost vapor film was achieved by making the surface of tiny steel spheres very water-repellant. The spheres were sprayed with a commercially available hydrophobic coating — essentially self-assembled nanoparticles — combined with other water-hating chemicals to achieve the right amount of roughness and water repellency. At the correct length scale this coating created a surface texture full of tiny peaks and valleys.

When the steel spheres were heated to 400 degrees Celsius and dropped into room temperature water, water vapors formed in the valleys of the textured surface, creating a stable Leidenfrost vapor film that did not collapse once the spheres cooled to the temperature of boiling water. In the experiments, researchers completely avoided the bubbly phase of boiling.

To contrast, the team also coated tiny steel spheres with a water-loving coating, heated the objects to 700 degrees Celsius, dropped them into room temperature water and observed that the Leidenfrost vapor collapsed with a vigorous release of bubbles.

The scientists have provided a video illustrating their work,

This movie shows the cooling of 20 mm hydrophilic (left) and superhydrophobic (right) steel spheres in 100 C water. The spheres’ initial temperature is about 380 C. The bubbling phase of boiling is completely eliminated for steel spheres with superhydrophobic coating. (from Vimeo, http://vimeo.com/49391913)

I understand there are advantages to not having bubbles in hot water but it somehow seems wrong. I’ve given up a lot over the years: gravity, boundaries between living and non-living (that was a very big thing to give up), and other distinctions that I have made based on traditional science but, today, this is one step too far.

It may seem silly but that memory of my mother explaining that you identify boiling water by its bubbles is important to me. It was one of my first science lessons. I imagine I will recover from this moment but it does remind me of how challenging it can be when your notions of reality/normalcy are challenged by various scientific endeavours. The process can get quite exhausting as you keep recalibrating everything you ‘know’ all the time.