Ion-Induced Friction Reduction in Water Nanoflow over Graphene

Our extensive nonequilibrium and equilibrium molecular dynamics simulations reveal the ion-induced interfacial friction reduction of NaCl-containing water nanoflow over graphene. Even under a normal pressure, with the increase in ion concentration, the friction coefficients of water nanoflow at the water/graphene interfaces decrease, and the slip lengths and shear viscosities of water nanoflow increase. The interfacial friction reduction with the increase in ion concentration is mainly attributed to the decrease in interfacial hydrated ions and the weaker binding of water molecules with graphene at a higher ion concentration. The presence of ions changes the hydrogen bond networks and structural configuration of water molecules close to the underlying graphene sheets and plays a key role in reducing the interfacial friction between water nanoflow and graphene.