Volatility effect on internal flow and contact line behavior during evaporation of binary mixture droplets

Selective evaporation of binary mixture droplets (BMDs), a phenomenon in which the more volatile com-ponents preferentially evaporate, affects contact line behavior, the total evaporation time, and internal flows, such as the solutal Marangoni flow. The surface tension gradient on a BMD is related to the local concentration of its constituents. We analyzed the dependence of the internal flow and contact line be-havior on the relative volatilities of the components of ethanol-water and ethylene glycol-water BMDs. Particle image velocimetry (PIV) and shadowgraph methods were simultaneously used to measure the in-ternal flow field and contact line behavior for a BMD, respectively. The results showed that the volatility properties of BMDs affect nonmonotonic contact line behavior during evaporation. Furthermore, the se-lective evaporation of a highly volatile component of BMDs results in vorticities, and internal circulation flow directions depend on the liquid composition. The averaged absolute vorticity was used to distinguish different stages of internal flow transitions of BMDs.(c) 2023 Elsevier Ltd. All rights reserved.