Strong Enhancement of Nanoconfined Water Mobility by a Structure Breaking Salt

Read how Naresh Osti, staff scientist, and Eugene Mamontov, senior scientist, describe differences in water mobility in confinement in a blink:

"In nature, water is present either in bulk form, confined in various media or in solution. Physico-chemical properties of water are dramatically different in those states and become very important in determining the fundamental processes associated with it, such as in energy storage applications as well as in transporting ions in biological membranes. It is important to explore the structure and dynamics of water associated with ions in bulk and in confinement at the molecular level to understand the fundamentals of not only the ion transport and energy storage mechanisms but also to advance the knowledge of bio-geo processes..

Therefore, the study of structure and dynamics of water always remains as an interesting topic in multiple research areas. Even though the dynamics of water in bulk and in various confinements have been studied for a long time using experimental, theoretical and simulations approaches, there is still a lot of interest in looking at the dynamics of water under different experimental conditions because of its unique behaviors that are not transferable from one condition to another. Therefore, in this research, we have explored the dynamics of water in confined aqueous salt solutions (NaCl and KCl) using quasielastic neutron scattering (QENS) for the first time.

Despite having same number of valance electrons, sodium forms a tight hydration shell around it compared to potassium, which facilitates breaking the hydrogen bond network of water and increasing the average translational mobility of water. However, KCl solutions experience the cumulative impact of the confinement and the presence of K+ ions, resulting in a 2-fold increase in the water diffusivity versus a few percent increase in the water diffusivity in the bulk solutions."