Macroscale Superlubricity and Polymorphism of Long-Chain <i>n</i>-Alcohols

Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviors under elastohydrodynamic lubrication (EHL) conditions, found inside bearings gears. Using tribometer, diamond anvil cell (DAC), differential scanning calorimetry (DSC) experiments, we that liquid 1-dodecanol undergoes a pressure-induced solidification when entrained into EHL contacts. Different solid polymorphs are formed the contact depending on temperature pressure conditions. Surprisingly, at moderate pressure, forms polymorph exhibits robust macroscale superlubricity. The DAC DSC experiments superlubricity is facilitated by formation of lamellar, hydrogen-bonded structures hexagonally close-packed molecules, which promote interlayer sliding. This novel mechanism similar to proposed for two-dimensional materials commonly employed lubricants, but it also enables practical advantages lubricants be maintained. When increased, polymorphic transformation phase gives higher friction. indicate high-friction an orthorhombic crystal. coincides with onset dimple in films, revealing film shapes caused rigid crystals contact. first demonstration lubricated nonaqueous arises from bulk effects rather than tribochemical transformations surfaces. Since observed here results transformations, continuously self-replenishing insensitive surface chemistry topology. discovery creates possibility implementing wide range machine components, would result enormous improvements efficiency durability.