Xiaolong Yang,Biao Qi,Yao Lu,Wang Zhang,Xiaolei Wang
Control of droplet sliding and its interfacial behavior such as sliding resistance and friction have important applications in microfluidic and energy-related fields. Nature provides many examples of interface-driven droplet sliding control; yet, to date, the continuous governing of the multiphase process and precise steering of droplet sliding remain challenging. Here, directional-dependent ultraslippery patterned surfaces with significant droplet sliding anisotropy were created by coordinating the heterogeneous wettability of the back of the dessert beetle, directional-dependent architecture of the butterfly wing, and ultraslippery configuration of the Nepenthes alata . Analysis of the sliding resistance on typical ultraslippery patterned surfaces reveals that the directional-dependent triple phase line (TPL) immigration on the ultraslippery patterns dominates the strong sliding anisotropy, which can be modeled using the classic Furmidge equation. In particular, the sliding anisotropy for the semicircular ultraslippery patterned surface shows threefold higher than that of natural butterfly wings due to the most significant difference in TPL immigration in two opposite directions, which enables the simultaneous handling of multiple droplets without mass loss and steering of droplet sliding/friction. This work may transform the design space for the control of multiphase interface motion and the development of new lab-on-a-chip and droplet-based microsystems.
Huaifang Qin,Liang Xu,Shiquan Lin,Fei Zhan,Kai Dong,Kai Han,Huamei Wang,Yawei Feng,Zhong Lin Wang
As an emerging technology for energy harvesting and distributed power supply, triboelectric nanogenerators are mainly based on a dielectric capacitive structure. Here, a new mechanism by introducing an oil phase into a water–solid interface is demonstrated for energy harvesting based on electric double layer (EDL) capacitance. Through squeezing and releasing oil droplets on a dielectric surface in water environment, charge transfer is observed in the back electrode accompanying the movement of the oil–water–solid three-phase line. The charge transfer is mainly attributed to the effect that the oil phase sweeps away ions near the dielectric surface in the EDL due to the discrepancy of EDL between water–solid and oil–solid interfaces. Under the water environment, the device is shown to be capable of direct energy harvesting and self-powered sensing without costly packaging. As a new working mode relying on EDL, it allows developing nanogenerators adaptive to severe environments even underwater with low friction and wear, and narrowing the gap between energy harvesting devices and electro-chemical devices. Through further enhanced EDL, it is reasonable to anticipate devices with an ultrahigh charge density comparable with EDL super capacitors, opening up an avenue toward new nanogenerators with overwhelming performance for practical applications ranging from blue energy harvesting to electro-catalysis.
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