From
ice superlubricity to quantum friction: Electronic repulsivity and phononic
elasticity
Friction 3(2015),294
Xi Zhang, Yongli Huang, Zengsheng Ma, Lengyuan Niu, Chang Qing Sun
Superlubricity
means non-sticky and frictionless when two bodies are set contacting motion.
Although this occurrence has been extensively investigated since 1859 when
Faraday firstly proposed a quasiliquid skin on ice, the mechanism behind the
superlubricity remains uncertain. This report features a consistent
understanding of the superlubricity pertaining to the slipperiness of ice,
self-lubrication of dry solids, and aqueous lubricancy from the perspective of
skin bond-electron-phonon adaptive relaxation. The presence of nonbonding
electron polarization, atomic or molecular undercoordination, and solute ionic
electrification of the hydrogen bond as an addition, ensures the superlubricity.
Nonbond vibration creates soft phonons of high magnitude and low frequency with
extraordinary adaptivity and recoverability of deformation. Molecular
undercoordination shortens the covalent bond with local charge densification,
which in turn polarizes the nonbonding electrons making them localized dipoles.
The locally pinned dipoles provide force opposing contact, mimicking magnetic
levitation and hovercraft. O:H−O bond electrification by aqueous ions has the
same effect of molecular undercoordination but it is throughout the entire body
of the lubricant. Such a Coulomb repulsivity due to the negatively charged skins
and elastic adaptivity due to soft nonbonding phonons of one of the contacting
objects not only lowers the effective contacting force but also prevents charge
from being transited between%