Transport of Water and Salt Through Desalination Membranes: A Computational Study

The dynamics of ions and solvent molecules in desalination membranes is key to water purification technologies in which selective transport of the different components are desired. Recent experimental results have shown that transport properties of ions in charged membranes are impacted by aqueous salt concentrations and ion identities. Motivated by such observations, here we have probed a series of atomistic molecular dynamics simulations of charged membranes in aqueous mono and divalent salt solutions at different concentrations (ranging from 0.06 to 1 M) to investigate the molecular level understanding the effects of multicomponent salt solutions on fundamental salt and water transport properties. Our finding shows that diffusion of salt ions and water are influenced by cation sizes, salt concentrations, and ionic strength of polymers. Divalent ions are more strongly coupled with ionic groups which reduce their motions as increasing concentration in fixed charged membranes. These simulations are in qualitative agreement with experimental results. Further, water molecules clustering around the ionic groups forms long-range networks in turn provide paths for salt transport and water diffusion.