Self-transporting of water drops on a pattern with hydrophilic hierarchical micropores and microchannels

Droplet transport has numerous engineering applications, including fog drop collecting and thermal management. However it remains a challenge to transport microscale droplet quickly and over long distances. Herein, based on inspirations from aquatic vegetation and nepenthes, a wedge-shaped pumpless platform(WSPP) for droplet transport is proposed. The WSPP consists of a superhydrophobic background, hydrophilic channels and micropore arrays. In WSPP, the micropore arrays can anchor a certain volume of droplets, generating a driving force to transport droplet along hydrophilic channels in two kinds of modes: dynamic transport and static transport. The optimized WSPP can transport droplets with a average distance of ∼18 mm at a average velocity of ∼17.5 mm/s through theoretical calculations and experimental analysis. Furthermore, by tuning the width of hydrophilic channels, the volume range of transported droplet can be easily regulated and the prepared surface can transport micro-sized droplets as well as millimeter-sized droplets at the same time. Finally, a new pumpless platform that several WSPPs with shaped gradient are cascaded via hydrophilic channels(CWSPP) is further prepared to improve micro-sized droplet transport performance in a relay way. We demonstrate the maximum self-transporting distance can even reach 35 mm with a velocity of ∼10.8 mm/s. In addition, the CWSPP has excellent anti-gravity pumping function with a tilting angle of 75°,a transport distance of 25 mm, only decreasing by 28.5％ compared with the horizontal that. We believe this work can provide an effect method to address challenges in condensing heat transfer and related engineering applications.