Research led by the University of Manchester’s National Graphene Institute, with the collaboration with IBEC, reveals that water that’s only a few molecules thick – like the water that covers every surface around us – behaves very differently to normal, ‘bulk’ water.
Water is one of the most fascinating substances on Earth. At the heart of its many unusual properties is its high polarizability – that is, its strong response to an applied electric field.
René Fábregas and Gabriel Gomila (IBEC)
Now, though, researchers have found that water that’s only a few molecules thick – like the water that covers every surface around us – behaves very differently to normal, ‘bulk’ water. Publishing in Science, they reveal that when in thin layers, water loses its polarizability, becoming electrically ‘dead’.
The research was led by Dr. Laura Fumagalli and Nobel Laureate Prof. Andre Geim, both at the National Graphene Institute at the University of Manchester, and involved IBEC group leader and Full Professor in the UB’s Department of Electronics and Biomedical Engineering Prof. Gabriel Gomila, as well as a group at Japan’s National Institute for Materials Science.
Using some new techniques, the researchers were able to measure, for the first time ever, the dielectric properties of water that is only a few molecules thick – and demonstrated that these atomically thin layers of water near solid surfaces do not respond to an electric field.
The finding has very important implications for the understanding of many phenomena where water is involved, including all living things.
For many decades scientists had tried without success to figure out how water behaves on a microscopic scale in the immediate vicinity of other substances, solid surfaces and macromolecules. “A layer of water only a few atoms thick covers every surface,” says lead author Dr. Fumagalli. “We can’t see it, but it is there, and its nature has been much debated for almost a century.”
Until now, this surface water was presumed to behave differently from normal water, which is famous for its anomalously high dielectric constant. Such water was predicted to exhibit a reduced electric response, but by how much remained unknown; and until now, it was a controversial issue in modern physical chemistry.
To resolve the debate, the collaborators had to develop new tools to controllably measure the dielectric constant on a very small scale. “To study the properties of this water, one needs to get rid from the effects of the bulk water that dominates its overall behavior,” says Prof. Gomila, who leads IBEC’s Nanoscale bioelectrical characterization group.
To achieve this, the scientists created special channels that were only several angstroms in size and which accommodated only a few layers of water, and then introduced a technique capable of probing water’s dielectric constant inside these nanochannels.
To their astonishment, the researchers found that the electric response of the confined water is not only suppressed but completely absent. In other words, the water inside nanochannels was electrically ‘dead’, with its dipoles immobilized and unable to screen an external field. This is in contrast to bulk water, whose molecules easily align along an electric field. The thickness of the dead layer was found to be less than one nanometer – that is, two to three molecules thick.
“This anomaly is not just an academic curiosity, but has clear implications for many fields, and for the life sciences in particular,” says Prof. Andre Geim, who was awarded the Nobel Prize for Physics in 2010. “Electric interactions with water molecules play an important role in shaping biological molecules such as proteins, so our results can help to improve the understanding of the role of water in technological processes, and why it is so crucial for life.”
The work was supported by Engineering and Physical Sciences Research Council, Lloyd’s Register Foundation, Royal Society, Graphene Flagship, European Research Council, Ministerio de Industria, Economia y Competitividad (MINECO) and ICREA Academia Award.
L. Fumagalli, A. Esfandiar, R. Fabregas, S. Hu, P. Ares, A. Janardanan, Q. Yang, B. Radha, T. Taniguchi, K. Watanabe, G. Gomila, K. S. Novoselov, A. K. Geim (2018). Anomalously low dielectric constant of confined water. Science, 22 Jun 2018: Vol. 360, Issue 6395, pp. 1339-1342. DOI: 10.1126/science.aat4191