Simulations and experiments can provide detailed information about the motion of water in salt water. Experiments can be used to measure the properties of water, such as its density and viscosity, and to study the effects of different parameters, such as temperature and pressure, on water’s motion.
Scientists at New York University and the Sorbonne have conducted calculations and experiments that show that water molecules travel swiftly around salt ions in saltwater solutions at a rate of more than a trillion times per second.
“There is more to salt solutions than meets the eye,” said Alexej Jerschow, a professor in NYU’s Department of Chemistry and one of the study’s senior authors. “This was evident when we both measured and modeled the very fast dynamics of sodium chloride ions and surrounding water molecules.”
The discoveries, which were reported in Nature Communications, would enable scientists to create more trustworthy models for predicting ion dynamics, which might be applied to a number of scientific projects, from enhancing rechargeable batteries to MRIs.
Ions are ubiquitous and critical to life. Numerous ions, including sodium and potassium, are widely distributed throughout the human body and control tissue structural integrity, nerve signaling, and cell viability. Another important factor is how ions interact with solvents; for example, rechargeable batteries depend on the movement of ions through electrolyte solutions.
Four to six water molecules usually surround ions in a water-based solution, however, it is unclear how much these molecules move together and how much motion the water molecules themselves go through. The coordinated motion between water and the ions has not been adequately modeled in the past.
The scientists combined the experimental data with thorough computer simulations that can simulate the dynamics around salt ions on an atomic scale in order to study the movement of salt and water molecules. The researchers used nuclear magnetic resonance (NMR) spectroscopy, a versatile technique that is frequently used to determine the structure of molecules.
There is more to salt solutions than meets the eye. This was evident when we both measured and modeled the very fast dynamics of sodium chloride ions and surrounding water molecules.
Professor Alexej Jerschow
The scientists noticed that water molecules move around the sodium and chloride ions at an incredibly fast rate more than a trillion times per second while testing salt water over a wide variety of concentrations and temperatures and combining experimental results with computer calculations.
The experiment also demonstrated that the ion-water complex, which was previously thought to move as a single unit with the surrounding solvent molecules, does not move as quickly as the water molecules.
“We found excellent agreement between experiment and simulations, which allows us to build reliable models for ion dynamics,” said Jerschow.
“We are now turning to more complex electrolytes and to 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 Centre national de la recherche scientifique (CNRS), and the study’s other senior author.
“We anticipate that this work can provide insights in many areas from medicine to energy storage that builds on a good understanding of ion dynamics in solution,” added Jerschow.
Overall, simulations and experiments are effective methods for figuring out how water behaves in salt water, which can help us comprehend the oceans and the climate of the Earth.
The National Institutes of Health (R01EB026456), European Research Council (863473), and National Science Foundation (CHE2108205) supported the research.
