Vapor-Induced Attraction of Floating Droplets.

Droplets partially submersed in an immiscible liquid pool attract each other. We experimentally study the interaction of floating droplets containing aqueous solution of a volatile liquid. A droplet affects its neighbors by generating a vapor gradient to the surroundings and responds by evaporating asymmetrically over its exposed cap. We show that the induced asymmetric temperature distribution causes a surface tension gradient driving the attracting motion. We highlight that the attracting dynamics starts with an accelerating stage, followed by a decelerating stage. We finally provide a theoretical model that quantitatively captures the interactive forces between droplets and predicts essential features of the attracting motion.