Groundbreaking research shows that water molecules at the surface of saltwater behave differently than previously thought, opening new perspectives for environmental science and technology. Textbook models will need to be redrawn after a group of researchers discovered that water molecules on the surface of saltwater are organized differently than previously thought.

Many important reactions related to climate and environmental processes occur where water molecules interact with air. For example, the evaporation of ocean water plays an important role in atmospheric chemistry and climate science. Understanding these reactions is critical to reducing human impact on our planet.

The distribution of ions at the interface between air and water can influence atmospheric processes. However, a precise understanding of the microscopic reactions at these important interfaces is still intensely debated.

Innovative research methods

In an article published today (January 15) in the magazine Nature Chemistry Researchers from the University of Cambridge and the Max Planck Institute for Polymer Research in Germany have shown that ions and water molecules on the surface of most saltwater solutions, known as electrolyte solutions, are organized in a very different way than traditionally understood. This could lead to better models of atmospheric chemistry and other applications.

The researchers decided to investigate how water molecules are affected by the distribution of ions at the point where air and water meet. Traditionally this has been done using a technique called Oscillatory Frequency Summation Generation (VSFG). With this laser technique, molecular vibrations can be measured directly at these key interfaces. However, although the strength of the signals can be measured, the method does not measure whether the signals are positive or negative; This has made interpretation of results difficult in the past. Additionally, using only experimental data may yield uncertain results.

The team overcame these challenges by using a more complex form of VSFG, called heterodyne-detected (HD)-VSFG, to study different electrolyte solutions. They then developed advanced computer models to simulate interfaces in various scenarios.

Revolution of traditional models

The combined results showed that both positively charged ions, called cations, and negatively charged ions, called anions, were depleted at the water/air interface. The cations and anions of simple electrolytes direct water molecules both up and down. This is a change from textbook models that teach that ions form an electrical double layer, directing water molecules in only one direction.

Co-author Dr. from Yusuf Hamid Department of Chemistry. Yair Litman said: “Our study shows that the surface of simple electrolyte solutions has a different ion distribution than previously thought, and that the ion-rich bottom surface determines how the interface is organized: several layers of pure water at the top, followed by a layer enriched with ions, and finally There is also a salt solution.’

Co-author Dr. from the Max Planck Institute. “This paper demonstrates that combining high-level HD-VSFG with simulations is an invaluable tool for advancing the understanding of liquid interfaces at the molecular level,” said Kuo-Yang Chiang.

Professor Misha Bonn, head of the Molecular Spectroscopy Unit at the Max Planck Institute, added: “Such interfaces are found all over the planet, so studying them not only helps our fundamental understanding but can also lead to better devices and technologies. Potential in batteries and energy storage “We apply the same techniques to study solid-liquid interfaces that may have applications.”