Superlubricity Between Alkane Molecules and Graphite: Effect of Alkane Chain Length

Graphite used as an oil lubricant additive demonstrates superior friction-reducing capability, but the optimal oil molecular structure for achieving the best lubrication state remains debated. In this study, the synergistic lubrication between alkane molecules with different chain lengths and graphite is investigated and compared using atomic force microscopy (AFM), scanning tunneling microscopy (STM), and molecular dynamics (MD) simulations. Superlubricity occurred in the hexadecane environment with an extremely low friction coefficient of 0.001, representing a reduction of over 80% compared to the dodecane (µ = 0.006) and nonane (µ = 0.009) environments. The observed structural superlubricity arises from the ordered alignment of long-chain alkane molecules along the zigzag direction of the graphite surface, which promotes the formation of stable confined molecular layers. Furthermore, their boundary slip on the graphite surface with low energy barriers contributes to the realization of ultralow friction. This observation elucidates the critical role of alkane chain length in modulating the synergistic lubrication mechanism of graphite nanoflakes, providing fundamental guidance for designing high-performance lubrication systems.