Carbon and water form a quantum couple; the progression of water on a carbon surface is represented by an uncommon peculiarity named quantum contact. This phenomenon, which was predicted in a previous theoretical study, is experimentally demonstrated at the interface between liquid water and graphene, a single layer of carbon atoms, in a new study that was published in Nature Nanotechnology. Progressed ultrafast procedures were utilized to play out this review. Applications in water purification and desalination processes and possibly even liquid-based computers may result from these findings.
How water behaves near carbon surfaces has baffled scientists for two decades. It could flow much more quickly than conventional flow theories predict, or it could form odd arrangements like square ice. Now, in a study that was published on June 22, 2023, in Nature Nanotechnology, a group of international researchers from the Max Plank Institute for Polymer Research in Mainz, Germany, the Catalan Institute of Nanoscience and Nanotechnology (ICN2, Spain), and the University of Manchester, England, report that water can interact directly with the electrons of carbon, a quantum phenomenon that is very unusual in fluid dynamics.
“It’s fascinating to see how the carrier dynamics of graphene continue to surprise us with unexpected mechanisms, this time involving solid-liquid interactions with molecules other than the ubiquitous water,”
Prof Klaas-Jan Tielrooij from ICN2 (Spain) and TU Eindhoven (The Netherlands).
Small molecules that move at random and constantly collide with one another make up a liquid like water. In contrast, a solid is made up of atoms that are well-arranged and bathed in an electron cloud. Since liquid molecules do not “see” the electrons of solid molecules, it is assumed that the only way the solid and liquid worlds interact is through collisions between their molecules. However, just over a year ago, a paradigm-shifting theoretical study proposed that the electrons of the solid and the molecules of the liquid push and pull on one another at the water-carbon interface, slowing the flow of the liquid. Quantum friction was the new term for this phenomenon. However, there was no experimental validation of the theoretical proposal.
Dr. Nikita Kavokine, who is a researcher at the Max Planck Institute in Mainz and the Flatiron Institute in New York, is the study’s lead author and states, “We have now used lasers to see quantum friction at work.” A single monolayer of carbon atoms arranged in a honeycomb pattern was the focus of the team’s research on a sample of graphene. The graphene’s electron cloud was instantly heated with ultrashort red laser pulses that lasted only a millionth of a billionth of a second. Terahertz laser pulses, which are sensitive to the temperature of the graphene electrons, were then used to monitor its cooling. Optically pump-terahertz probe (OPTP) spectroscopy is the name given to this method.
When graphene was submerged in water, the electron cloud cooled more quickly, surprising them; submerging graphene in ethanol had no effect on the rate of cooling. “We still had to understand what exactly was going on,” Kavokine says, “even though this was yet another indication that the water-carbon couple is somehow special.” One possible explanation is that the water molecules are warmed up by the hot electrons pressing and pulling on them. Simply put, they cool down as a result of quantum friction. The researchers looked into the theory, and it turned out that water-graphene quantum friction might be able to explain the data from the experiments.
Prof. Klaas-Jan Tielrooij of ICN2 (Spain) and TU Eindhoven (The Netherlands) says, “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.” The fact that water’s vibrations—called hydrons—are in sync with those of the graphene electrons—called plasmons—enhances the effect of resonance that enhances heat transfer between graphene and water.
As a result, the experiments show that quantum friction between liquids and solids works as intended. Quantum friction could be used to adjust the nanoporous membranes’ permeation properties in filtration and desalination processes because of this. First author Xiaoqing Yu, a Ph.D. student at the Max Planck Institute in Mainz, says, “Our findings are not only interesting for physicists, but they also hold potential implications for electrocatalysis and photocatalysis at the solid-liquid interface.”
The discovery was made by combining a theoretical framework, a measurement instrument, and an experimental system that rarely work together. Gaining control over the water-electron interaction is the main obstacle right now. According to Kavokine, “Our goal is to turn on and off quantum friction on demand.” We might be able to create fluid-based computers or smarter water filtration processes in this way.”
More information: Xiaoqing Yu et al, Electron cooling in graphene enhanced by plasmon–hydron resonance, Nature Nanotechnology (2023). DOI: 10.1038/s41565-023-01421-3
