Tag Archives: Max Planck Institute for Polymer Research

Water talks to electrons in graphene (i.e., carbon)?

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Institutions from Spain, Germany, and England collaborated on the study announced in this June 23, 2023 news item on Nanowerk, Note: A link has been removed,

For the last 20 years, scientists have been puzzled by how water behaves near carbon surfaces. It may flow much faster than expected from conventional flow theories or form strange arrangements such as square ice.

Now, an international team of researchers from the Max Plank Institute for Polymer Research of Mainz (Germany), the Catalan Institute of Nanoscience and Nanotechnology (ICN2, Spain), and the University of Manchester (England), reports in a study published in Nature Nanotechnology (“Electron cooling in graphene enhanced by plasmon–hydron resonance”) that water can interact directly with the carbon’s electrons: a quantum phenomenon that is very unusual in fluid dynamics.

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Pictured above: Water-graphene quantum friction (Credits: Lucy Reading-Ikkanda / Simons Foundation)

There are two press releases with almost identical text, the June 22, 2023 Max Planck Institute press release with its additional introductory paragraph is below,

Water and carbon make a quantum couple: the flow of water on a carbon surface is governed by an unusual phenomenon dubbed quantum friction. A work published in ‘Nature Nanotechnology’ experimentally demonstrates this phenomenon – which was predicted in a previous theoretical study— at the interface between liquid water and graphene, a single layer of carbon atoms. Advanced ultrafast techniques were used to perform this study. These results could lead to applications in water purification and desalination processes and maybe even to liquid-based computers.

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A liquid, such as water, is made up of small molecules that randomly move and constantly collide with each other. A solid, in contrast, is made of neatly arranged atoms that bathe in a cloud of electrons. The solid and the liquid worlds are assumed to interact only through collisions of the liquid molecules with the solid’s atoms: the liquid molecules do not “see” the solid’s electrons. Nevertheless, just over a year ago, a paradigm-shifting theoretical study proposed that at the water-carbon interface, the liquid’s molecules and the solid’s electrons push and pull on each other, slowing down the liquid flow: this new effect was called quantum friction. However, the theoretical proposal lacked experimental verification.

“We have now used lasers to see quantum friction at work,” explains study lead author Dr Nikita Kavokine, a researcher at the Max Planck Institute in Mainz and the Flatiron Institute in New York. The team studied a sample of graphene – a single monolayer of carbon atoms arranged in a honeycomb pattern. They used ultrashort red laser pulses (with a duration of only a millionth of a billionth of a second) to instantaneously heat up the graphene’s electron cloud. They then monitored its cooling with terahertz laser pulses, which are sensitive to the temperature of the graphene electrons. This technique is called optical pump – terahertz probe (OPTP) spectroscopy.

To their surprise, the electron cloud cooled faster when the graphene was immersed in water, while immersing the graphene in ethanol made no difference to the cooling rate. “This was yet another indication that the water-carbon couple is somehow special, but we still had to understand what exactly was going on,” Kavokine says. A possible explanation was that the hot electrons push and pull on the water molecules to release some of their heat: in other words, they cool through quantum friction. The researchers delved into the theory, and indeed: water-graphene quantum friction could explain the experimental data.

“It’s fascinating to see that the carrier dynamics of graphene keep surprising us with unexpected mechanisms, this time involving solid-liquid interactions with molecules none other than the omnipresent water,” comments Prof Klaas-Jan Tielrooij from ICN2 (Spain) and TU Eindhoven (The Netherlands). What makes water special here is that its vibrations, called hydrons, are in sync with the vibrations of the graphene electrons, called plasmons, so that the graphene-water heat transfer is enhanced through an effect known as resonance.

The experiments thus confirm the basic mechanism of solid-liquid quantum friction. This will have implications for filtration and desalination processes, in which quantum friction could be used to tune the permeation properties of the nanoporous membranes. “Our findings are not only interesting for physicists, but they also hold potential implications for electrocatalysis and photocatalysis at the solid-liquid interface,” says Xiaoqing Yu, PhD student at the Max Planck Institute in Mainz and first author of the work.

The discovery was down to bringing together an experimental system, a measurement tool and a theoretical framework that seldom go hand in hand. The key challenge is now to gain control over the water-electron interaction. “Our dream is to switch quantum friction on and off on demand,” Kavokine says. “This way, we could design smarter water filtration processes, or perhaps even fluid-based computers.”   

The almost identical June 26, 2023 University of Manchester press release is here.

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

Electron cooling in graphene enhanced by plasmon–hydron resonance by Xiaoqing Yu, Alessandro Principi, Klaas-Jan Tielrooij, Mischa Bonn & Nikita Kavokine. Nature Nanotechnology (2023) DOI: https://doi.org/10.1038/s41565-023-01421-3 Published: 22 June 2023

This paper is open access.

Organic neuromorphic electronics

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A December 13, 2021 news item on ScienceDaily describes some research from Germany’s Max Planck Institute for Polymer Research,

The human brain works differently from a computer – while the brain works with biological cells and electrical impulses, a computer uses silicon-based transistors. Scientists have equipped a toy robot with a smart and adaptive electrical circuit made of soft organic materials, similarly to the biological matter. With this bio-inspired approach, they were able to teach the robot to navigate independently through a maze using visual signs for guidance.

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A December 13, 2021 Max Planck Institute for Polymer Research press release (also on EurekAlert), which originated the news item, fills in a few details,

The processor is the brain of a computer – an often-quoted phrase. But processors work fundamentally differently than the human brain. Transistors perform logic operations by means of electronic signals. In contrast, the brain works with nerve cells, so-called neurons, which are connected via biological conductive paths, so-called synapses. At a higher level, this signaling is used by the brain to control the body and perceive the surrounding environment. The reaction of the body/brain system when certain stimuli are perceived – for example, via the eyes, ears or sense of touch – is triggered through a learning process. For example, children learn not to reach twice for a hot stove: one input stimulus leads to a learning process with a clear behavioral outcome.

Scientists working with Paschalis Gkoupidenis, group leader in Paul Blom’s department at the Max Planck Institute for Polymer Research, have now applied this basic principle of learning through experience in a simplified form and steered a robot through a maze using a so-called organic neuromorphic circuit. The work was an extensive collaboration between the Universities of Eindhoven [Eindhoven University of Technology; Netherlands], Stanford [University; California, US], Brescia [University; Italy], Oxford [UK] and KAUST [King Abdullah University of Science and Technology, Saudi Arabia].

“We wanted to use this simple setup to show how powerful such ‘organic neuromorphic devices’ can be in real-world conditions,” says Imke Krauhausen, a doctoral student in Gkoupidenis’ group and at TU Eindhoven (van de Burgt group), and first author of the scientific paper.

To achieve the navigation of the robot inside the maze, the researchers fed the smart adaptive circuit with sensory signals coming from the environment. The path of maze towards the exit is indicated visually at each maze intersects. Initially, the robot often misinterprets the visual signs, thus it makes the wrong “turning” decisions at the maze intersects and loses the way out. When the robot takes these decisions and follows wrong dead-end paths, it is being discouraged to take these wrong decisions by receiving corrective stimuli. The corrective stimuli, for example when the robot hits a wall, are directly applied at the organic circuit via electrical signals induced by a touch sensor attached to the robot. With each subsequent execution of the experiment, the robot gradually learns to make the right “turning” decisions at the intersects, i. e. to avoid receiving corrective stimuli, and after a few trials it finds the way out of the maze. This learning process happens exclusively on the organic adaptive circuit. 

“We were really glad to see that the robot can pass through the maze after some runs by learning on a simple organic circuit. We have shown here a first, very simple setup. In the distant future, however, we hope that organic neuromorphic devices could also be used for local and distributed computing/learning. This will open up entirely new possibilities for applications in real-world robotics, human-machine interfaces and point-of-care diagnostics. Novel platforms for rapid prototyping and education, at the intersection of materials science and robotics, are also expected to emerge.” Gkoupidenis says.

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

Organic neuromorphic electronics for sensorimotor integration and learning in robotics by Imke Krauhausen, Dimitrios A. Koutsouras, Armantas Melianas, Scott T. Keene, Katharina Lieberth, Hadrien Ledanseur, Rajendar Sheelamanthula, Alexander Giovannitti, Fabrizio Torricelli, Iain Mcculloch, Paul W. M. Blom, Alberto Salleo, Yoeri van de Burgt and Paschalis Gkoupidenis. Science Advances • 10 Dec 2021 • Vol 7, Issue 50 • DOI: 10.1126/sciadv.abl5068

This paper is open access.

Structural memory of water and the picosecond timescale

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Water is a unique liquid and researchers from Germany and the Netherlands can detail at least part of why that’s so according to a Sept. 18, 2015 news item on Nanowerk,

A team of scientists from the Max Planck Institute for Polymer Research (MPI-P) in Mainz, Germany and FOM Institute AMOLF in the Netherlands have characterized the local structural dynamics of liquid water, i.e. how quickly water molecules change their binding state. Using innovative ultrafast vibrational spectroscopies, the researchers show why liquid water is so unique compared to other molecular liquids. …

With the help of a novel combination of ultrafast laser experiments, the scientists found that local structures persist in water for longer than a picosecond, a picosecond (ps) being one thousandth of one billionth of a second ((1012 s). This observation changes the general perception of water as a solvent.

A Sept. 18, 2015 Max Planck Institute for Polymer Research press release (also on EurekAlert), which originated the news item, details the research,

… “71% of the earth’s surface is covered with water. As most chemical and biological reactions on earth occur in water or at the air water interface in oceans or in clouds, the details of how water behaves at the molecular level are crucial. Our results show that water cannot be treated as a continuum, but that specific local structures exist and are likely very important” says Mischa Bonn, director at the MPI-P.

Water is a very special liquid with extremely fast dynamics. Water molecules wiggle and jiggle on sub-picosecond timescales, which make them undistinguishable on this timescale. While the existence of very short-lived local structures – e.g. two water molecules that are very close to one another, or are very far apart from each other – is known to occur, it was commonly believed that they lose the memory of their local structure within less than 0.1 picoseconds.

The proof for relatively long-lived local structures in liquid water was obtained by measuring the vibrations of the Oxygen-Hydrogen (O-H) bonds in water. For this purpose the team of scientists used ultrafast infrared spectroscopy, particularly focusing on water molecules that are weakly (or strongly) hydrogen-bonded to their neighboring water molecules. The scientists found that the vibrations live much longer (up to about 1 ps) for water molecules with a large separation, than for those that are very close (down to 0.2 ps). In other words, the weakly bound water molecules remain weakly bound for a remarkably long time.

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

Strong frequency dependence of vibrational relaxation in bulk and surface water reveals sub-picosecond structural heterogeneity by Sietse T. van der Post, Cho-Shuen Hsieh, Masanari Okuno, Yuki Nagata, Huib J. Bakker, Mischa Bonn & Johannes Hunger. Nature Communications 6, Article number: 8384 doi:10.1038/ncomms9384 Published 18 September 2015

This is an open access paper,

Sea sponges inspire body armour of the future

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A Mar. 15, 2013 news item on ScienceDaily features research inspired by sea sponges,

Scientists at Johannes Gutenberg University Mainz (JGU) and the Max Planck Institute for Polymer Research (MPI-P) in Germany have created a new synthetic hybrid material with a mineral content of almost 90 percent, yet extremely flexible. They imitated the structural elements found in most sea sponges and recreated the sponge spicules using the natural mineral calcium carbonate and a protein of the sponge. Natural minerals are usually very hard and prickly, as fragile as porcelain.

Amazingly, the synthetic spicules are superior to their natural counterparts in terms of flexibility, exhibiting a rubber-like flexibility. The synthetic spicules can, for example, easily be U-shaped without breaking or showing any signs of fracture. …

Spicules are structural elements found in most sea sponges. They provide structural support and deter predators. They are very hard, prickly, and even quite difficult to cut with a knife. The spicules of sponges thus offer a perfect example of a lightweight, tough, and impenetrable defense system, which may inspire engineers to create body armors of the future.

I found an image of a sea sponge (this may not be exactly the same type of sponge that inspired the latest work but I think there are enough similarities to the description the researchers give to  include it here) and more information in a Nov. 13, 2008 post by Ed Grabianows on IO9.com,

Downloaded from: http://io9.com/5085064/giant-deep-sea-sponges-evolved-fiber-optic-exoskeletons

Downloaded from: http://io9.com/5085064/giant-deep-sea-sponges-evolved-fiber-optic-exoskeletons

This gigantic sea sponge has an exoskeleton made of glass rods, and each rod can grow up to a meter in length. In the deep sea, these massive sponges contain a menagerie of other tiny lifeforms, all dependent on their sea sponge hosts for something in short supply far under the water. They need light – and some sponges have a [sic] evolved a way to provide it using fiber optics.Sea sponges are among the most primitive animals on Earth. …

Here’s more about the research (from the ScienceDaily news item),

 The researchers led by Wolfgang Tremel, Professor at Johannes Gutenberg University Mainz, and Hans-Jürgen Butt, Director at the Max Planck Institute for Polymer Research in Mainz, used these natural sponge spicules as a model to cultivate them in the lab. The synthetic spicules were made from calcite (CaCO3) and silicatein-α. The latter is a protein from siliceous sponges that, in nature, catalyzes the formation of silica, which forms the natural silica spicules of sponges. Silicatein-α was used in the lab setting to control the self-organization of the calcite spicules. The synthetic material was self-assembled from an amorphous calcium carbonate intermediate and silicatein and subsequently aged to the final crystalline material. After six months, the synthetic spicules consisted of calcite nanocrystals aligned in a brick wall fashion with the protein embedded like cement in the boundaries between the calcite nanocrystals. The spicules were of 10 to 300 micrometers in length with a diameter of 5 to 10 micrometers.

… the synthetic spicules have yet another special characteristic, i.e., they are able to transmit light waves even when they are bent.

The researchers have created a video animation to illustrate their work,

For those who would like to find out more about the research, there’s a citation for and a link to the researchers’ paper here.

Halleluiah! one step closer to self-cleaning glass

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I cannot tell you the joy this news gives me. From the Dec. 6, 2011 news item on Nanowerk,

Eyeglasses need never again to be cleaned, and dirty windscreens are a thing of the past! Researchers at the Max Planck Institute for Polymer Research in Mainz and the Technical University Darmstadt are now much closer to achieving this goal. They have used candle soot to produce a transparent superamphiphobic coating made of glass (“Candle Soot as a Template for a Transparent Robust Superamphiphobic Coating”). Oil and water both roll off this coating, leaving absolutely nothing behind. Something that even held true when the researchers damaged the layer with sandblasting. The material owes this property to its nanostructure. Surfaces sealed in this way could find use anywhere where contamination or even a film of water is either harmful or just simply a nuisance.

Actually, I’m hoping for a little more than eye glasses—I never want to wash another window or mirror. More from the news item,

The coating essentially consists of an extremely simple material: silica, the main constituent of all glass. The researchers coated this with a fluorinated silicon compound, which already makes the surface water and oil repellent, like a non-stick frying pan. The really clever part is the structure of the coating, however. This is what makes the glass super water repellent and super oil repellent. In a frying pan with this type of coating, water and oil would simply roll around in the form of drops. The structure of the layer resembles a sponge-like labyrinth of completely unordered pores, which is made up of tiny spheres.

Such a coating would be ideal for numerous applications, not least because it is so easy to produce. “We can even produce it in jam jars,” says Doris Vollmer [head of a research group at the Max Planck Institute for Polymer Research]. And the soot from a candle flame, from which the researchers made something akin to a glass imprint, served as the model for the porous structure of the spheres. The researchers began by holding a glass slide in a flame so that the soot particles, which measure around 40 nanometres in diameter, formed a sponge-like structure on the glass. The next step was to coat it with silica in a glass vessel – even a jam jar would do – by vapour depositing a volatile organic silicon compound and ammonia onto the soot deposit. When they subsequently heated the material, the soot decomposed. The next step was to vapour deposit a fluorinated silicon compound as well onto the hollow silica structure.

They then attempted to wet this coating with different liquids. However, they didn’t succeed, even when they let hexadecane drip from a great height onto it; in a non-stick frying pan, hexadecane spreads out like water in a washbasin. “Initially, a drop of the oil penetrated into the sponge-like structure, but then bounced back like a rubber ball,” explains Doris Vollmer. Although a portion of the liquid remained in the pores and wet the material, when most of the drop returned to the surface at a slower speed after bouncing up, it drew the small amount of the hexane that had remained out of the glass pores again. Finally, the reunited drop remained lying on the surface like a ball. The researchers in Mainz tested the superamphiphobic layer with a total of seven liquids and found that none was sucked up by the glass sponge.

Sadly, it seems I will have to wait a bit longer as there is no mention of a product being commercialized now or in the near future.