Quantum Friction Governs the Flow of Water on a Carbon Surface, New Study Reveals

In physics, water and carbon make a good pair governed by a strange phenomenon called quantum friction. For the past two decades, experts have been baffled by the behavior of water near carbon surfaces. It could flow much faster than expected from traditional flow theories or form strange patterns such as square ice. A new research study demonstrates this event at the intersection between liquid water and graphene.

The Unusual Nature of Water-Carbon Interface

An international group of researchers from the Catalan Institute of Nanoscience and Nanotechnology in Spain, the Max Plank Institute for Polymer Research of Mainz in Germany, and the University of Manchester in England confirmed the ability of water to interact with the electrons of carbon directly. This quantum event is a very unusual occurrence in fluid dynamics.

A previous theoretical study tried to explain the water-carbon interface. It was assumed that solids and liquids could only interact through the collisions of the molecules of liquid with the atoms of solid. The paradigm-shifting research proposed that liquid molecules and solid electrons, known as quantum friction, push and pull each other in effect. However, this suggestion has not been experimentally verified yet.

To witness quantum friction at work, Dr. Nikita Kavokine led the research team to study a graphene sample using a technique known as the optical pump-terahertz probe (OPTP) spectroscopy. Using ultrashort red laser pulses, the graphene's electron cloud was heated up instantaneously. As it cools, it is monitored using terahertz laser pulses known for being sensitive to the temperature of graphene's electrons.

The team observed that the cloud of electrons cooled faster upon immersing graphene in water. Meanwhile, immersing graphene in ethanol does not change the cooling rate. Surprisingly, the water used in this experiment shows vibrations that are in sync with the vibrations of the graphene electrons. The vibrations allow the graphene-water heat transfer to be enhanced by resonance.

The result of the study connects a measurement tool, an experimental system, and a theoretical framework which do not usually come together. The researchers are hopeful that their discovery will impact filtration and desalination processes. These actions use quantum friction in tuning the permeation behaviors of nanoporous membranes.

Does Quantum Friction Really Exist?

Quantum friction is a theory that predicts that the movement of two uncharged polarized bodies relative to each other experience a quantum force that tends to resist the relative motion. Assumed to take place even at zero temperature, this effect is also predicted to occur when the surfaces of the moving bodies are flat and regarded as continuous media.

In other words, the idea of quantum friction describes two materials moving past each other which experience lateral forces arising from quantum variation in the vacuum. For several decades, experts have been intrigued if quantum friction exists. It was previously calculated that this event could happen from the Casimir force between two plates.

A group of scientists from the UK performed detailed investigations and claimed that there is no lateral force, and quantum friction does not exist. However, another group of scientists also assumes that there is a need for a lateral force between the plates in the form of quantum-mechanical friction. They propose that the changes in reflection or the bouncing of electromagnetic waves alter the perpendicular component of the Casimir force.

In a study conducted by John Pendry of Imperial College in London, he claims that he has experimentally observed the quantum-frictional effects in the resistance of a material made of two field-effect transistors.