Superlubricity was also observed between a gold AFM tip and Teflon substrate due to repulsive Van der Waals forces and hydrogen-bonded layer formed by glycerol on the steel surfaces. Formation of the hydrogen-bonded layer was also shown to lead to superlubricity between quartz glass surfaces lubricated by biological liquid obtained from mucilage of Brasenia schreberi. Other mechanisms of superlubricity may include: (a) thermodynamic repulsion due to a layer of free or grafted macromolecules between the bodies so that the entropy of the intermediate layer decreases at small distances due to stronger confinement; (b) electrical repulsion due to external electrical voltage; (c) repulsion due to electrical double layer; (d) repulsion due to thermal fluctuations.