Cold self-lubrication of sliding ice

The low kinetic friction between ice and numerous counterbodies is commonly attributed to an interfacial water layer, which is believed to originate from pre-existing surface water or from melt water induced by high contact pressures or frictional heat. However, even the currently leading theory of frictional melting appears to defy direct experimental verification. Here we present molecular simulations of ice interfaces that reveal that ice surfaces liquefy without melting thermodynamically but predominantly by cold, displacement-driven amorphization. Despite effective self-lubrication, very small ice friction is found to require water to slip past a hydrophobic counterface -- or an excess amount of water, produced by, e.g., extreme sliding velocities.