Simulations and experiments reveal unprecedented detail about the movement of water in salt water

In salt water solutions, water molecules move rapidly around salt ions on a scale of more than a trillion times per second, according to experiments and simulations led by scientists at NYU and the Sorbonne.

“There are more solutions to salt than meets the eye,” said Alexej Jerschow, a professor in the Department of Chemistry at New York University and one of the study’s senior authors. “This was evident when we measured and modeled the very fast dynamics of the surrounding NaCl ions and water molecules.”

Results published in Nature Communicationswill allow researchers to build more reliable models for predicting the dynamics of ions, which can be used in a variety of scientific endeavors, than to improve rechargeable batteries to an MRI.

Ions are ubiquitous and essential to life. Many ions, such as sodium and potassium, diffuse through human body Cell viability, nerve signaling, and the structural integrity of tissues are dictated. How the ions interact with the solvent also plays an important role; For example, rechargeable batteries rely on the movement of ions through electrolyte solutions.

Ions in an aqueous 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 the water molecules experience. Previously used models were insufficient in capturing the coordinated motion between water and ions.

To study the movement of salt and water molecules, researchers used it NMR (Nuclear Magnetic Resonance), a versatile tool that is routinely used to determine the structure of molecules, and to combine experimental data with details Computer simulation that can model the dynamics around it salt ions on an atomic scale.

Testing salt water over a wide range of concentrations and temperatures, and combining experimental data with computer simulations, the researchers observed that water molecules oscillate around sodium and chloride ions at an extremely fast rate — more than a trillion times per second. In addition, it was previously assumed that the ions move with the surrounding solvent molecules as a single unit, but experiment has shown that this is not the case; Instead, it is water molecules Much faster oscillation than compound ionic water.

“We found excellent agreement between experiment and simulation, which allows us to build reliable models of ion dynamics,” Gershaw said.

“We are now moving on to more complex electrolytes and to what happens near solid surfaces, and the combination of experiments and simulations will again be necessary to make progress,” said Benjamin Rotenberg of the Sorbonne and the National Center for Scientific Research (CNRS) in France. The other lead author of the study.

“We anticipate that this work can provide insights in many areas – from medicine to… Energy storage“That builds on a good understanding of the dynamics of the ions in solution,” Gershaw added.