Stagnation Point of Surface Flow during Drop Evaporation.

Capillary flow and Marangoni flow influence flow patterns of an evaporating liquid drop. While it is obvious that Marangoni stress on the drop surface affects the surface flow direction, we found that capillary flow also has an impact. The numerical results of this study showed a stagnation point near the contact line, which was further explained by the lubrication theory. The stagnation point is produced by the competing effects of Marangoni flow and capillary flow and emerges when the contact angle is small because the divergence of the capillary flow near the contact line increases as the contact angle decreases. The radial position of the stagnation point from the numerical results ( rnumerical ≈ 0.995) agreed with the experimentally observed stagnation point ( rexperimental > 0.992).