Friction increases with load. This is Amontons' first law, validated at macroscopic scales for three centuries, and it matches intuition — press harder and things grip more. The proportionality constant is the friction coefficient: a number that describes the surface pair and stays roughly constant as you vary the force.
At the nanoscale, borate ionic liquids on graphite violate this. At low loads, the friction coefficient is moderate — around 0.023. As normal load increases past approximately thirty nanonewtons, corresponding to about 2.4 gigapascals of contact pressure, the friction coefficient drops by an order of magnitude to 0.0013. The surfaces enter a superlubric state. Pressing harder makes things more slippery (ACS Sustainable Chemistry & Engineering, 2026).
The mechanism is molecular reorganization. The borate anions have long alkyl chains — hydrocarbon tails that can adopt many conformations. At low pressure, these chains are disordered. They interlock with the graphite surface and with each other, creating structural resistance to sliding. When the load exceeds the threshold, the pressure forces the alkyl chains to align — lying flat, parallel, ordered. The interlocking disappears. The interface transforms from a rough, tangled boundary to a smooth, aligned one.
Critically, this is not chemistry. AFM-IR and angle-resolved XPS confirm no tribochemical reaction occurs. No bonds break or form. The molecules don't change — they rearrange. The transition is mechanical, not chemical: the load is sufficient to overcome the entropic preference for disorder and impose geometric order on the interfacial layer. It is a pressure-driven phase transition confined to a molecular film.
The general principle: friction is not a property of two surfaces. It is a property of what happens at their boundary, and boundaries can reorganize. In this system, the disordered boundary layer is what causes friction, and sufficient pressure eliminates the disorder that causes the friction. The applied force destroys the very structure that resists the applied force.
This is a load-triggered instability — the system's response to increased stress is to undergo a structural transition that reduces its resistance. The harder you push, the less resistance you encounter, but only above a threshold. Below it, friction behaves normally. The superlubric regime is hidden behind a pressure barrier that everyday experience never crosses.