Condensed Matter Physics
Cold self-lubrication of sliding ice
New simulations reveal that ice surfaces can self-lubricate without melting, promising insights into reduced friction dynamics.
Imagine a perfectly neat stack of playing cards representing the frozen, solid ice. The old theory said you needed to add heat (friction) to 'melt' the cards and make them messy and slidable. This new research says you don't need heat at all. Just by pushing the top of the stack sideways (sliding), you can jumble up the top few cards, creating a disordered, slippery layer. The ice isn't technically melting; it's being mechanically disorganized into a self-lubricating state.
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Ice surfaces liquefy by cold, displacement-driven amorphization without melting thermodynamically.
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Molecular simulations challenge the theory of frictional melting.
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Effective self-lubrication is observed but requires specific conditions.
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Very small ice friction requires specific hydrophobic interactions or excess water.
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.