How Cations - Silica Surface Interactions Affect Water Dynamics in Nanoconfined Electrolyte Solutions

Probing electrolytes behavior at the atomic level provides valuable insights into understanding the reactive transport of electrolyte solutions in nanoconfinement and help explaining and predicting the macroscopic properties of industrial or natural nanoporous materials. In this study, we focused on the behavior of water and ions in 2.6 nm silica nanocylinders filled with electrolyte solutions, XCl at 1M with X = Li, Na and Cs, monovalent cations presenting various kosmotropic/chaotropic properties. Using a combination of experiments and theoretical modeling, we analyzed the water dynamics based on three primary effects: the confinement, the electrolyte, and the interfacial ions-porous material surface interaction. Comparing the water dynamics obtained with divalent cations previously studied by Baum et al., we highlight that monovalent cations present weaker interactions with silica surfaces than divalent cations. This significantly impacts the water dynamics in addition to the confinement and electrolyte effects. This study pinpoints the importance of ions behavior within the interfacial layer and its impact on water transport in nanoconfinement.