In saltwater solutions, water molecules move rapidly around salt ions at a scale of more than a trillion times per second, according to experiments and simulations led by scientists at New York University and the Sorbonne.
“There is more to salt solutions than meets the eye,” said Alexej Jerschow, a professor in New York University’s Department of Chemistry and one of the study’s lead authors. “This was evident when we measured and modeled the very fast dynamics of sodium chloride ions and the surrounding water molecules.”
The findings, published in nature communicationsIt will allow researchers to build more reliable models for predicting ion dynamics, which could be used for a variety of scientific endeavors, from improving rechargeable batteries to MRIs.
Ions are ubiquitous and critical to life. Many ions, such as sodium and potassium, are found throughout the human body and dictate cell viability, nerve signaling, and the structural integrity of tissues. The way in which the ions interact with the solvents also plays a fundamental role; for example, rechargeable batteries are based on the movement of ions through electrolyte solutions.
Ions in a water-based solution are usually surrounded by four to six water molecules, but it is not well understood how far these molecules move as a unit and how much movement water molecules experience. Previously used models have been inadequate to capture the concerted movement between water and ions.
To study the movement of water and salt molecules, the researchers used nuclear magnetic resonance (NMR) spectroscopy, a versatile tool commonly used to determine the structure of molecules, and combined the experimental data with detailed computer simulations that they can model the dynamics around salt ions on the atomic scale.
Testing salt water at a wide range of concentrations and temperatures, and combining experimental data and computer simulations, the researchers observed that water molecules move around sodium and chloride ions at an extremely fast rate, over a trillion times. times per second. Also, it was previously assumed that the ions move together with the surrounding solvent molecules as a unit, but experiment showed that this is not the case; instead, water molecules move much faster than the ion-water complex.
“We found excellent agreement between the experiment and the simulations, allowing us to build reliable models for ion dynamics,” Jerschow said.
“We are now turning to more complex electrolytes and what happens near solid surfaces, and combining experiments with simulations will once again be essential to move forward,” said Benjamin Rotenberg of the Sorbonne Université and the Center national de la recherche scientifique (CNRS). ) from France, and the other lead author of the study.
“We anticipate that this work can provide insights in many areas, from medicine to energy storage, that are based on a good understanding of ion dynamics in solution,” Jerschow added.
The research was supported by the National Institutes of Health (R01EB026456), the European Research Council (863473), and the National Science Foundation (CHE2108205).