Janus gate: A unique topology blocks the flow of water in one direction but makes it run fast in the opposite direction.

Droplet impacting on solid or liquid interfaces is a ubiquitous phenomenon in nature. Although complete rebound of droplets is widely observed on superhydrophobic surfaces, the bouncing of droplets on liquid is usually vulnerable due to easy collapse of entrapped air pocket underneath the impinging droplet. Here, we report a superhydrophobic-like bouncing regime on thin liquid film, characterized by the contact time, the spreading dynamics, and the restitution coefficient independent of underlying liquid film. Through experimental exploration and theoretical analysis, we demonstrate that the manifestation of such a superhydrophobic-like bouncing necessitates an intricate interplay between the Weber number, the thickness and viscosity of liquid film. Such insights allow us to tune the droplet behaviours in a well-controlled fashion. We anticipate that the combination of superhydrophobic-like bouncing with inherent advantages of emerging slippery liquid interfaces will find a wide range of applications.

Energy harvesting devices that prosper in harsh environments are highly demanded in a wide range of applications ranging from wearable and biomedical devices to self-powered and intelligent systems. Particularly, over the past several years, the innovation of triboelectric nanogenerators (TENGs) that efficiently convert ambient kinetic energy of water droplets or wave power to electricity has received growing attention. One of the main bottlenecks for the practical implications of such devices originates from the fast degradation of the physiochemical properties of interfacial materials under harsh environments. To overcome these challenges, here we report the design of a novel slippery lubricant-impregnated porous surface (SLIPS) based TENG, referred to as SLIPS-TENG, which exhibits many distinctive advantages over conventional design including optical transparency, configurability, self-cleaning, flexibility, and power generation stability, in a wide range of working environments. Unexpectedly, the slippery and configurable lubricant layer not only serves as a unique substrate for liquid/droplet transport and optical transmission, but also for efficient charge transfer. Moreover, we show that there exists a critical thickness in the liquid layer, below which the triboelectric effect is almost identical to that without the presence of such a liquid film. Such an intriguing charge transparency behavior is reminiscent of the wetting transparency and van der Waals potential transparency of graphene previously reported, though the fundamental mechanism remains to be elucidated. We envision that the marriage of these two seemingly totally different arenas (SLIPS and TENG) provides a paradigm shift in the design of robust and versatile energy devices that can be used as a clean and longer-lifetime alternative in various working environments.

Nickel cobalt sulfide (NiCo ₂ S ₄ ) is a promising battery-type material for electrochemical energy storage.

Despite extensive progress, current icephobic materials are limited by the breakdown of their icephobicity in the condensation frosting environment. In particular, the frost formation over the entire surface is inevitable as a result of undesired inter-droplet freezing wave propagation initiated by the sample edges. Moreover, the frost formation directly results in an increased frost adhesion, posing severe challenges for the subsequent defrosting process. Here, we report a hierarchical surface which allows for interdroplet freezing wave propagation suppression and efficient frost removal. The enhanced performances are mainly owing to the activation of the microscale edge effect in the hierarchical surface, which increases the energy barrier for ice bridging as well as engendering the liquid lubrication during the defrosting process. We believe the concept of harnessing the surface morphology to achieve superior performances in two opposite phase transition processes might shed new light on the development of novel materials for various applications.

The directional and long-range droplet transportation is of great importance in microfluidic systems. However, it usually requires external energy input. Here we designed a wettability gradient surface that can drive droplet motion by structural topography. The surface has a wettability gradient range of over 150° from superhydrophobic to hydrophilic, which was achieved by etching silicon nanopillars and adjusting the area of hydrophilic silicon dioxide plane. We conducted force analysis to further reveal the mechanism for droplet self-propulsion, and found that the nanostructures are critical to providing a large driving force and small resistance force. Theoretical calculation has been used to analyze the maximal self-propulsion displacement on different gradient surfaces with different volumes of droplets. On this basis, we designed several surfaces with arbitrary paths, which achieved directional and long-range transportation of droplet. These results clarify a driving mechanism for droplet self-propulsion on wettability gradient surfaces, and open up new opportunities for long-range and directional droplet transportation in microfluidic system.