No abstract

The behavior of droplets trapped in geometric structures is essential to droplet manipulation applications such as for droplet transport. Here we show that directional droplet movement can be realized by a V-shaped groove with the movement direction controlled by adjusting the surface wettability of the groove inner wall and the cross sectional angle of the groove. Experiments and analyses show that a droplet in a superhydrophobic groove translates from the immersed state to the suspended state as the cross sectional angle of the groove decreases and the suspended droplet departs from the groove bottom as the droplet volume increases. We also demonstrate that this simple grooved structure can be used to separate a water-oil mixture and generate droplets with the desired sizes. The structural effect actuated droplet movements provide a controllable droplet transport method which can be used in a wide range of droplet manipulation applications.

No abstract

Self-propelled droplet jumping plays a crucial role in numerous applications such as condensation heat transfer, self-cleaning, and water harvesting. Compared to individual droplet jumping, the coalescence-induced droplet jumping in a domino manner has attracted more attention due to its potential for the high performance of droplet mobility and heat transfer. However, there is an apparent gap in the current literature regarding the demonstration of the advantage of this preferred droplet transport in a well-controlled way. In this study, we report the attainment of droplet jumping relay by designing a nanosheet-covered superhydrophobic surface with V-shaped macrogrooves (Groove-SHS). We find that the macrogroove arrays can significantly modify the droplet dynamics in the presence of a non-condensable gas (NCG) by coupling rapid droplet growth and efficient droplet removal by jumping relay. The condensate droplets formed through the NCG diffusion layer on top of the cones and between the grooves serve as more efficient conduits for heat transfer. The droplets with higher mobility formed on the bottom of the grooves can undergo a series of coalescence which results in the preferred droplet jumping relay. Such a droplet jumping relay can induce a considerable vibration for triggering the removal of droplets on top of the cones. The condensation performance of the Groove-SHS is increased by 60% compared to that of the flat superhydrophobic surface due to the synergistic effect of rapid droplet growth and efficient droplet removal facilitated by the integration of the droplet jumping relay. The mechanisms revealed in this work pave the way for dropwise condensation enhancement.