Ice friction at the nanoscale

TL;DR

This study uses computer simulations to explore the atomic-scale mechanisms of ice friction, revealing how premelting layers and substrate interactions influence slipperiness across temperatures and pressures.

Contribution

It provides the first detailed atomistic understanding of ice friction, highlighting the roles of premelting, pressure, and substrate hydrophobicity or hydrophilicity.

Findings

Premelting layers of ~1 nm provide lubrication with bulk-like properties.

Hydrophobic surfaces exhibit large slip, hydrophilic surfaces show stick boundary conditions.

Pressure and frictional heating significantly affect ice's lubricating behavior.

Abstract

The origin of ice slipperiness has been a matter of great controversy for more than a century, but an atomistic understanding of ice friction is still lacking. Here, we perform computer simulations of an atomically smooth substrate sliding on ice. In a large temperature range between 230 and 266 K, hydrophobic sliders exhibit a premelting layer similar to that found at the ice air interface. On the contrary, hydrophilic sliders show larger premelting and a strong increase of the first adsorption layer. The non equilibrium simulations show that premelting films of barely one nanometer thickness are sufficient to provide a lubricating quasi liquid layer with rheological properties similar to bulk undercooled water. Upon shearing, the films display a pattern consistent with lubricating Couette flow, but the boundary conditions at the wall vary strongly with the substrates interactions. Hydrophobic walls exhibit large slip, while hydrophilic walls obey stick boundary conditions with small negative slip. By compressing ice above atmospheric pressure, the lubricating layer grows continuously, and the rheological properties approach bulk-like behavior. Below 260 K, the equilibrium premelting films decrease significantly. However, a very large slip persists on the hydrophobic walls, while the increased friction on hydrophilic walls is sufficient to melt ice and create a lubrication layer in a few nanoseconds. Our results show the atomic scale frictional behavior of ice is a combination of spontaneous premelting, pressure melting and frictional heating.