Cunming Yu

Hydrophobic/Hydrophilic Cooperative Janus System for Enhancement of Fog Collection.

Harvesting micro-droplets from fog is a promising method for solving global freshwater crisis. Different types of fog collectors have been extensively reported during the last decade. The improvement of fog collection can be attributed to the immediate transportation of harvested water, the effective regeneration of the fog gathering surface, etc. Through learning from the natures strategy for water preservation, the hydrophobic/hydrophilic cooperative Janus system that achieved reinforced fog collection ability is reported here. Directional delivery of the surface water, decreased re-evaporation rate of the harvested water, and thinner boundary layer of the collecting surface contribute to the enhancement of collection efficiency. Further designed cylinder Janus collector can facilely achieve a continuous process of efficient collection, directional transportation, and spontaneous preservation of fog water. This Janus fog harvesting system should improve the understanding of micro-droplet collection system and offer ideas to solve water resource crisis.

Superhydrophobic helix: controllable and directional bubble transport in an aqueous environment

Manipulating air bubbles in an aqueous medium exhibits both scientific and technologic value in gas-collection, selective aeration, and pollutant disposal. Superhydrophobic substrates, known as underwater superaerophilic substrates, offer numerous opportunities to develop advanced gas controlling systems, arising from its strong affinity to air bubbles in water. Herein, we present a superhydrophobic helix that is able to achieve controllable and directional bubble delivery. In an aqueous environment, the bubble tends to stay on the summit of the helix structure and moves along with the helix rotation. The velocity of the bubble delivery can be facilely tuned in terms of the spacing length of the helix. Continuous bubble collection and delivery were realized by integrating the helix with a gas needle and anti-buoyancy transport of the air bubbles was demonstrated using a tilted superhydrophobic helix. Taking advantage of the bubble controllability, a bubble based micro-reaction of H2 and O2 was conducted depending on the special helix structure with two directionalities. This contribution should provide new ideas for the exploration of functional superwettability materials and promote the development of gas-involved multi-phase systems.

Unidirectional water delivery on a superhydrophilic surface with two-dimensional asymmetrical wettability barriers

A superhydrophilic surface decorated with 2D hydrophobic water barriers is proven to be a potential platform for unidirectional liquid transport. Differing from the existing systems based on 3D micro-structures, this functional surface features a simplified structure and high adaptiveness that provide more possibilities for the development of fluid manipulating materials.

Bioinspired Pressure-Tolerant Asymmetric Slippery Surface for Continuous Self-Transport of Gas Bubbles in Aqueous Environment

Biosurfaces with geometry-gradient structures or special wettabilities demonstrate intriguing performance in manipulating the behaviors of versatile fluids. By mimicking natural species, that is, the cactus spine with a shape-gradient morphology and the Picher plant with a lubricated inner surface, we have successfully prepared an asymmetric slippery surface by following the processes of CO2-laser cutting, superhydrophobic modification, and the fluorinert infusion. The asymmetric morphology will cause the deformation of gas bubbles and subsequently engender an asymmetric driven force on them. Due to the infusion of fluorinert, which has a low surface energy (∼16 mN/m, 25 °C) and an easy fluidic property (∼0.75 cP, 25 °C), the slippery surface demonstrates high adhesive force (∼300 μN) but low friction force on the gas bubbles. Under the cooperation of the asymmetric morphology and fluorinert infused surface, the fabricated asymmetric slippery surface is applicable to the directional and continuous bubble delivery in an aqueous environment. More importantly, due to the hard-compressed property of fluorinert, the asymmetric slippery surface is facilitated with distinguished bubble transport capability even in a pressurized environment (∼0.65 MPa), showing its feasibility in practical industrial production. In addition, asymmetric slippery surfaces with a snowflake-like structure and a star-shaped structure were successfully fabricated for the real-world applications, both of which illustrated reliable performances in the continuous generation, directional transportation, and efficient collection of CO2 and H2 microbubbles.

Foolproof Method for Fast and Reversible Switching of Water-Droplet Adhesion by Magnetic Gradients

Reversible switching of water-droplet adhesion on solid surfaces is of great significance for smart devices, such as microfluidics. In this work, we designed a foolproof method for fast and reversible magnet-controlled switching of water-droplet adhesion surfaces by doping iron powders in soft poly(dimethylsiloxane). The water adhesion is adjusted by magnetic field-induced structure changes, avoiding complex chemical or physical surface design. The regulation process is so convenient that only tens of milliseconds are needed. The on-site responsive mechanism extends its use to unusual curved surfaces. Moreover, the excellent reversibility and stability make the film an ideal candidate for real-time applications.

Is Superhydrophobicity Equal to Underwater Superaerophilicity: Regulating the Gas Behavior on Superaerophilic Surface via Hydrophilic Defects

Superhydrophobic surfaces have long been considered as superaerophilic surfaces while being placed in the aqueous environment. However, versatile gas/solid interacting phenomena were reported by utilizing different superhydrophobic substrates, indicating that these two wetting states cannot be simply equated. Herein, we demonstrate how the hydrophilic defects on the superhydrophobic track manipulate the underwater gas delivery, without deteriorating the water repellency of the surface in air. The versatile gas-transporting processes can be achieved on the defected superhydrophobic surfaces; on the contrary, in air, a water droplet is able to roll on those surfaces indistinguishably. Results show that the different media pressures applied on the two wetting states determine the diversified fluid-delivering phenomena; that is, the pressure-induced hydrophilic defects act as a gas barrier to regulate the bubble motion behavior under water. Through the rational incorporation of hydrophilic defects, a series of gas-transporting behaviors are achieved purposively, for example, gas film delivery, bubble transporting, and anisotropic bubble gating, which proves the feasibility of this underwater air-controlling strategy.

Hierarchical hydrophilic/hydrophobic cooperative fog collector possessing self-pumped droplet delivering ability

Harvesting micro-droplets from fog flow has emerged as a promising strategy for supplying clean water in foggy but arid regions. Ideal fog harvesting devices should possess both high efficiency for fog collection and an economic process of water accumulation. To optimize the water transporting pathway in gravity-driven fog collectors, here we present a hierarchical hydrophilic/hydrophobic (3H) cooperative fog collecting surface with the function of self-pumped droplet absorption. The directional water delivery completely depends on the surface energy release of the hanging droplets with a spherical shape. This 3H fog harvesting surface, composed of upright steel needles, hydrophilic foam of melamine resin and hydrophobic silica stripes, exhibits enhanced fog collecting ability, i.e., four times higher than that of the pristine hydrophilic foam surface and two times higher than that of the hydrophilic/hydrophobic surface without a hierarchical structure. More importantly, the pathway of water preservation is improved to overcome the drawback of traditional systems. Fog-water can be effectively captured by the protrusion structure and subsequently absorbed by the hydrophilic foam driven by the wettability gradient. Further incorporation of striped water barriers promotes one-way water transport even against gravity. Propelled by the surface energy, this 3H fog collector can achieve a gravity-independent process of efficient fog capture, directional water delivery, and rapid water storage all in one step. This design gives an example of advanced fog harvesting interfaces and can extend the application scope of self-propelled fluid delivery systems.