The dry friction coefficient increased with waiting time, as mentioned in (35). The change in the dry friction coefficient within the time window of measurement was only a few percent (1.05×), while the change in the lubricated friction coefficient was almost two times compared with the initial value. Thus, we neglected the change of the dry friction coefficient with time in our measurements.

The dry friction coefficient increased by only a few percent with increase in roughness. Meanwhile, the change in lubricated friction coefficient (Fig. 3B) was almost fivefold. Thus, the change of the friction coefficient with roughness can be neglected. Currently, we are studying these phenomena in more detail.