Evaporation and liquid-phase separation of ethanol-cyclohexane binary drops under acoustic levitation

Evaporation of cyclohexane and ethanol binary drops under acoustic levitation was investigated. The aim was to understand the effect of acoustic levitation on the evaporation dynamics and involved physical processes of the binary drops. We report the occurrence of liquid-phase separation of the binary drop during evaporation under acoustic levitation. Through systematic experiments, it was found that the enhanced evaporation rate of the drop under acoustic levitation led to a significant temperature decrease. In addition, driven by external acoustic streaming, water vapor tended to be enriched and condensed on the drop surface. Because ethanol is extremely soluble in water, tiny cyclohexane droplets were extracted from ethanol owing to water condensation. In addition, driven by the internal flow of the acoustically levitated drop, the extracted cyclohexane droplets coalesced, eventually resulting in macro-segregation in the drop. These findings provide new insights into the evaporation dynamics of acoustically levitated drops, thus, shedding light on industrial purification and separation of volatile liquids with opposite water solubilities, such as cyclohexane and ethanol.