Non-uniform absorption and evaporation at a droplet interface

A water droplet on a solid substrate can evaporate and simultaneously absorb vapors from the surrounding atmosphere. If alcohol vapors are near the water droplet, the vapour-driven solutal Marangoni flows are generated, which can be used for various applications including droplet splitting, mixing, and coating. To control the solutal Marangoni flow, it is important to understand the molecule transport at the vapor-liquid interface. We believe that the vapour absorption and evaporation should be considered at the same time. However, it has been rarely investigated for these features. Thus, in this work, we experimentally and numerically investigated how the solutal Marangoni flow patterns changed depending on vapor distributions and different absorption conditions. Both experimental and numerical results showed that the absorption and evaporation rates are non-uniform along the radial direction and the two phenomena competed each other, so that the internal flow structures were changed depending on the contact angle of the droplet and the alcohol vapor source location. During the talk, physical arguments will be provided to explain the working mechanism of the solutal Marangoni flow.