Impact of elastic instabilities on friction induced by capillary adhesion

Transient high friction force usually appears when a hard sphere slides on a soft substrate during the water evaporation. Such a special wetting condition featuring the friction enhancement, even exceeding the friction of dry condition, is termed as tacky regime. Herein, the impact of Schallamach waves on the friction enhancement induced by capillary adhesion is investigated by integrating microtribometer measurements, interference microscopy visualization, and finite element analysis. It is found that the friction peak decreases or even disappears with decreasing elastic modulus of soft substrate, which is attributed to the nucleation and propagation of Schallamach waves. The increase of friction during the tacky transition depends on the competition between capillary adhesion and stress relief of Schallamach wave.