Effect of hydrated ions and wettability on ice friction

Ice friction is a vital phenomenon in both fundamental research and practical applications. However, one unsolved puzzle regarding ice friction is the effect of hydrated ions and wettability on its tribological properties. Here, we report the effects of the extent of hydrated ions, surface wettability, and their combination on ice friction. By selecting the type and concentration of ions, the coefficients of ice friction were reduced by more than 70%. Experimental spectra, low-field nuclear magnetic resonance (LF-NMR), density functional theory (DFT) calculations, and molecular dynamics (MD) simulations demonstrated that the addition of ions could break H-bonds. For negatively charged surfaces, cations play an important role in ice friction. Ionic ice has a lower friction coefficient because of the repulsive force of hydration, and more free water molecules are produced by H-bond breaking. Wettability regulates ice friction coefficients by changing the adhesion between water and solids, and a hydrophilic surface results in a stronger adhesion force. The regulation of surface wettability can modulate ice friction by approximately 20%. Compared with that of hydrated ions, the ability to regulate wettability to modulate the ice friction coefficient is relatively weak. This study provides guidance for the selection of ions and surface wettability to modulate ice friction.