Ultraconfinement of aqueous electrolytic solutions within hydrophilic nanotubes

Abstract

By means of molecular simulations we shed light on the interplay of surface, confinement and salt effects on the structure and dynamics of water and ions highly confined within a hydrophilic silica nanotube. By a local description of the hydrogen bonding network, the structure and the dynamics we disentangle the confinement and the surface effects. In general, the concentration dependence of the structure and the dynamics is strongly exacerbated under high confinement. Thus, the confinement effect enhances the formation of Na–Cl clusters which strongly affect the dynamics of water. We show that the interlayer which corresponds to a minimum in radial density is linked to an unexpected increase in the hydrogen bonds number while dynamically we highlight a subdiffusive regime together with an increase of the interfacial dipolar relaxation time for water molecules as the NaCl concentration increases. Energetically speaking we demonstrate that the cohesion of the HB network decreases significantly under highly restrictive geometry.