Light Droplet Levitation in Relation to Interface Morphology and Liquid Property.

Light droplet levitation is an elegant technique allowing for contact-less manipulation in a wall-free environment. However, direct generation of light levitated droplets remains limited by small-curvature interface and underlying mechanism remains unclear. Here we report that small-curvature interface limitation encountered in liquid water is overcome by using liquids with extremely small saturated vapor pressure, which allows for direct generation of light levitated droplets above large-curvature interface. It is demonstrated that the interface morphology and extremely small saturated vapor pressure of liquids together contribute to creation of the gravity-lift and evaporation-condensation balances, enabling droplet levitation even above large-curvature interface. We also propose a levitation number Lv to judge whether droplets can be directly levitated above a curved interface or not, which successfully predicts the occurrence of light droplet levitation. When Lv falls in the range of 2.25 × 10 -4 ∼ 6 × 10 -3 , tiny condensed droplets can be stably levitated above the gas-liquid interface no matter interface morphology and liquid type. The study deepens the understanding of the underlying mechanism for generating light levitated droplets.