In saltwater solutions, water molecules move rapidly around salt ions at rates of more than a trillion times per second, according to both experiments and simulations led by scientists at New York University and the Sorbonne.
“There’s more to saline solutions than meets the eye,” said Alexei Yershov, a professor in the NYU Department of Chemistry and one of the lead authors of the study. “This became clear when we both measured and modeled the very fast dynamics of sodium chloride ions and surrounding water molecules.”
The results, published in nature communicationwill allow researchers to create more reliable models to predict ion dynamics that could be used in a variety of scientific endeavors, from improving rechargeable batteries to MRIs.
Ions are ubiquitous and essential to life. Many ions, such as sodium and potassium, are ubiquitous in the human body and determine cell viability, nerve signaling, and the structural integrity of tissues. How ions interact with solvents also plays a crucial role; for example, rechargeable batteries rely on the movement of ions through electrolyte solutions.
Ions in a water-based solution are typically surrounded by four to six water molecules, but the extent to which these molecules move as a unit and how much movement the water molecules experience is not well understood. Previously used models were insufficient to capture the concerted motion between water and the ions.
To study the movement of salt and water molecules, the researchers used nuclear magnetic resonance (NMR) spectroscopy, a versatile tool routinely used to determine the structure of molecules, and combined the experimental data with detailed computer simulations modeling the dynamics can salt ions at the atomic level.
Testing saltwater over a wide range of concentrations and temperatures, the researchers combined experimental data and computer simulations and observed that water molecules weave around the sodium and chloride ions at an extremely fast pace – more than a trillion times per second. In addition, it was previously assumed that ions move together with surrounding solvent molecules as a unit, but experiment showed that this is not the case; Instead, the water molecules wiggle much faster than the ion-water complex.
“We found excellent agreement between experiment and simulation, which allows us to build reliable models for ion dynamics,” said Jerschow.
“We are now turning to more complex electrolytes and what happens near solid surfaces, and combining experiments with simulations will again be essential to make progress,” said Benjamin Rotenberg of Sorbonne Université and France’s Center national de la recherche scientifique (CNRS). the other senior author of the study.
“We expect that this work can provide insights in many areas – from medicine to energy storage – that build on a good understanding of ion dynamics in solution,” added Jerschow.
The research was supported by the National Institutes of Health (R01EB026456), the European Research Council (863473) and the National Science Foundation (CHE2108205).