Water drop impingement on graphite substrates with random dilute defects

Droplet impingement experiments for a wide range of Weber numbers were conducted by digitizing silhouettes of impacting water drops onto a tailored grinded graphite substrate, typified by randomly distributed cavities on a generally smooth surface. The aim was to investigate if the anchoring of the triple line, due to friction forces generated by dilute superficial defects, could be observed for drop impingement experiments. During the early inertially dominated spreading phase, the drops showed similar behaviors independently of the initial impact velocities. However, just after this phase, droplets impacting at low Weber numbers indeed exhibited this peculiar friction-induced pinned configuration.