Effect of a structure breaking salt on the mobility of nanoconfined water

Structure and dynamics of water vary dramatically between bulk state, confined state, and solution impacting various processes associated with energy storage applications and the transport of ions in biological membranes. Here, using quasielastic neutron scattering technique, we have investigated the effect of confinement in 3 nm silica pores on water diffusivity in aqueous solutions of archetypical structure-making (kosmotrope) NaCl and structure-breaking (chaotrope) KCl salts, up to 1.0 M in concentration. The water diffusivity in bulk aqueous solutions in this concentration range is known to decrease very slightly in the presence of NaCl and increase very slightly in the presence of KCl. However, the water diffusivity in confined H2O-KCl increases by a factor of 2 compared to the pure water diffusivity in the same confinement. This unusually strong cumulative effect of confinement and a structure-breaking salt may have profound implications for the mobility and transport of aqueous species in nature and technological applications.