Evaporation-driven directed motion of droplets on the glass

Manipulating and guiding the droplet movement on a substrate by vapor-mediated actuation is a new approach for microfluidic devices. In this work, the evaporation-driven self-propulsion of the droplets such as N,N-dimethylacetamide, and N-methylformamide on the glass is demonstrated. By the addition of the Silwet surfactant, the aforementioned liquids change from total wetting to partial wetting and the two-component droplet is formed on the glass. The random walk behavior of the droplet can be directed by the linear and octagonal runways on a substrate, of which both hydrophobic sides are constructed by the polysilazane coating. The long-range transport of the droplet is observed, and the effect of the Silwet concentration on the self-propelled velocity is examined. Finally, the evaporation-driven mechanism is investigated by employing the open and closed environments for one-droplet and two-droplet systems. It is found that the self-propelled behavior of Silwet-laden droplets vanishes in the closed environment.