Gradient-Janus Wires for Simultaneous Fogwater Harvesting and Electricity Generation.

A Gradient-Janus wire (GJW) with a diameter of 0.3 mm has been fabricated on a large scale through liquid confined modification, enabling the opposite conical wetting phenomenon along the same orientation of the GJW, characterized by an increasing superhydrophilic region and a decreasing hydrophobic region. This property allows the GJW to exhibit controllable water hovering, transport, and pinning during fog harvesting, i.e., at a large tilting angle α of 60° (mass increased with decreased α), the GJW can hover 0.6 mg of harvested fogwater in 30 s, can transport 3 mg of fogwater along the gradient in 30 s at α = 4° (with maximal mass reaching up to 4.3 mg at α = -10°), and finally, pin the water droplet at the end of the GJW. Such ability generates an effective torque that serves as the driving force for rotation. We designed a GJWs-wheel by radially arranging 60 GJWs together, resulting in an extremely lightweight structure weighing only 1.9 g. The cumulative torque generated during fog harvesting activates the rotation of the GJWs-wheel. When loaded with a coil within a magnetic field, electricity is generated as output power peaks at around 0.25 µW while maintaining a high water harvesting efficiency averaging approximately 38 ± 2.12 mg/min. This finding is significant as it provides valuable insights into designing materials capable of efficiently harnessing both energy and water resources.

Robust Photothermal Icephobic Surface with Mechanical Durability of Multi-Bioinspired Structures.

Photothermal superhydrophobic surfaces are potential to become ideal anti-/deicing surfaces due to their rapid water removal, icing delay, and photothermal deicing performance. Here, a robust photothermal icephobic surface with mechanical durability is shown that is integrated with a microspine array inspired by honeycomb and cactus thorn (i.e., MAHC), which is developed by a laser-layered microfabrication strategy. The maximum stress on the microspine of the MAHC is reduced by ≈2/3, due to the protection of the bionic honeycomb structure. Even after 200 linear abrasions by a steel blade, the MAHC remains superior water repellency with a water contact angle of 150.7° and roll-off angles of 10.3°, stable icing delay time (578.2 s), and rapidly photothermal deicing capabilities (401 s). As the MAHC is fabricated on a curvature surface such as a copper alloy transmission line for an overhead high-speed rail, a stable photothermal anti-/deicing in a low-temperature environment still can be achieved effectively. The freezing rain covering the functional transmission line completely slides off within 758 s under one sun illumination. This studying offers insight into the design of novel materials with stable anti-icing/icephobic structures, which would be extended into some applied realms, for example, transportation fields or power systems in cold or low-temperature climates.

Highly Efficient Photothermal Icephobic/de-Icing MOF-Based Micro and Nanostructured Surface.

Photothermal materials have gained considerable attention in the field of anti-/de-icing due to its environmental friendliness and energy saving. However, it is always significantly challenging to obtain solar thermal materials with hierarchical structure and simultaneously demonstrate both the ultra-long icing delay ability and the superior photothermal de-icing ability. Here, a photothermal icephobic MOF-based micro and nanostructure surface (MOF-MNS) is presented, which consists of micron groove structure and fluorinated MOF nanowhiskers. The optimal MOF-M250 NS can achieve solar absorption of over 98% and produce a high temperature increment of 65.5 °C under 1-sun illumination. Such superior photothermal-conversion mechanism of MOF-M250 NS is elucidated in depth. In addition, the MOF-M250 NS generates an ultra-long icing delay time of ≈3960 s at -18 °C without solar illumination, achieving the longest delay time, which isn't reported before. Due to its excellent solar-to-heat conversation ability, accumulated ice and frost on MOF-M250 NS can be rapidly melted within 720 s under 1-sun illumination and it also holds a high de-icing rate of 5.8 kg m-2 h-1 . MOF-M250 NS possesses the versatility of mechanical robustness, chemical stability, and low temperature self-cleaning, which can synergistically reinforce the usage of icephobic surfaces in harsh conditions.

Efficient Atmospheric Water Harvesting of Superhydrophilic Photothermic Nanocapsule.

Drought and water scarcity are two of the world's major problems. Solar-powered sorption-based atmospheric water harvesting technology is a promising solution in this category. The main challenge is to design materials with high water harvesting performance while achieving fast water vapor adsorption/desorption rates. Here, a superhydrophilic photothermic hollow nanocapsule (SPHN) is represented that achieves efficient atmospheric water harvesting in outdoor climates. In SPHN, the hollow mesoporous silica (HMS) is grafted with polypyrrole (PPy) and also loaded with lithium chloride (LiCl). The hollow structure is used to store water while preventing leakage. The hydrophilic spherical nanocapsule and the trapped water produce more free and weakly adsorbed water. Significantly lower the heat of desorption compared to pure LiCl solution. Such SPHN significantly improves the adsorption/desorption kinetics, e.g., absorbs 0.78-2.01 g of water per gram of SPHN at 25 °C, relative humidity (RH) 30-80% within 3 h. In particular, SPHN has excellent photothermal properties to achieve rapid water release under natural sunlight conditions, i.e., 80-90% of water is released in 1 h at 0.7-1.0 kW m-2 solar irradiation, and 50% of water is released even at solar irradiation as low as 0.4 kW m-2 . The water collection capacity can reach 1.2 g g-1 per cycle by using the self-made atmospheric water harvesting (AWH) device. This finding provides a way to design novel materials for efficient water harvesting tasks, e.g., water engineering, freshwater generator, etc.

Elastic Microstaggered Porous Superhydrophilic Framework as a Robust Fogwater Harvester.

A robust fogwater harvester with an elastic microstaggered porous superhydrophilic framework (EMSF) has been designed. The EMSF can be fabricated by using polydimethylsiloxane and polyvinyl alcohol (PVA) via an etching method of sugar crystals pile-up cube as a template. The EMSF possesses a high porosity of 76%, of which the saturated fogwater-capturing capacity is 4 times higher than its weight, achieving a high fogwater harvesting rate (ε) of 62.7 g/cm3·h. It is attributed to the strong hydrogen bond (H-bond) interaction between hydroxyl groups (-OH) in PVA and water molecules for rapidly harvesting water and storing water in a staggered porous structure by means of a capillary force. The elasticity of EMSF allows to achieve a higher fogwater harvesting rate (ε) of 73.2 g/cm3·h via releasing the as-stored water in the EMSF under periodic external pressing. In addition, a durable corrosion resistance is demonstrated on the EMSF. This study offers a way to design novel materials that would further be extended into applications, for example, fog engineering in industry, agriculture, forest, and so forth.

Polysulfide microspheres with chemical modification for generation of interfaces with macroscopic colour variation and biomimetic superhydrophobicity.

Both superwettability and structural colours have attracted considerable attention in recent years. In addition, the combination of structural colours and superwettability could endow materials with broader application prospects. The combination provides a new strategy to design novel functional materials, and there are many studies pertaining to these materials that have been reported in recent years. Herein, a polysulfide (PSF) superhydrophobic coating was synthesized successfully. The PSF superhydrophobic coating possesses excellent superhydrophobicity, oleophobicity for diesel and macroscopic structural colour variation when wetted. The colour is changed when the coating is wetted and it returns to its original colour after drying. In addition, the surface presents better reusability and thermostability which satisfies various daily needs. The PSF superhydrophobic coating can be considered as an excellent candidate for designing wetting responsive materials, and it has enormous application potential in the fields of detection, sensing, anti-counterfeiting and security. For the first time, we present a novel and low-cost strategy to fabricate materials with both superhydrophobicity and structural colour, offering significant insights into the practical application of these functional materials.

Efficient Fog Harvesting Based on 1D Copper Wire Inspired by the Plant Pitaya.

The leaf of the plant pitaya shows excellent fog harvesting behavior through its 1D thorns with wire-like microstructures. The thorns of it cannot provide enough driving force for the droplet transportation by the special structure and chemistry gradient as the cactus thorns, but it showed efficient water supply which improved the fog harvesting greatly. The mechanism is studied based on 1D copper wire with similar 1D wire-like microstructure and wettability. This structure can significantly reduce the deviation of the fog-laden winds, and the surface intrinsic hydrophility makes water accumulate on it in the form of droplets, which endow it with an efficient water supply that is ∼100 times faster than that on a 2D-flat surface. In addition, it can also enhance the fog capture and water removal. The 3D fog collector composed of 1D microcopper wires has been fabricated which show a high fog harvesting efficiency of ∼13%. This work explains the role of 1D wire-like microstructure in efficient fog harvesting in a different view and provides new insight into the application of developing a more efficient fog collector.

Diving-floating locomotion induced by capturing and manipulating bubbles in an aqueous environment.

A superhydrophobic and superaerophilic surface was fabricated by facile self-assembly of silica nanoparticle/PDMS composites. The relevant superaerophilic surface showed excellent adhesion to air bubbles in an aqueous environment. With bubbles adhering to the superaerophilic surface, the density of the whole system was adjustable, which was applied to induce a diving-floating locomotion in an aqueous environment.

Novel fabrication of polymer/carbon nanotube composite coated Janus paper for humidity stress sensor.

In this work, we constructed a sensing system on Janus paper with hydrophilic side and hydrophobic side via depositing polymer precursor onto one side of qualitative filter paper. Water in humid environment (including liquid water, condensed moisture airflow and gaseous humid atmosphere) will be captured and gathered in the hydrophilic region of Janus paper due to the asymmetric hydrophobicity and hygroscopicity, which can induce the novel directional deformation. Additionally, MWCNTs (multiwalled carbon nanotubes) were loaded onto hydrophobic region beforehand to construct conductive network. The resistance of the conductive network changes synergistically as the Janus paper deforms in humid environment. Thus, the novel Janus paper realized the induction of environment humid factors, and conversion from the deformation signals to the desirable electric signals. The Janus paper also shows excellent stability in cycle use.

Understanding how surface chemistry and topography enhance fog harvesting based on the superwetting surface with patterned hemispherical bulges.

The Namib Desert beetle-Stenocara can adapt to the arid environment by its fog harvesting ability. A series of samples with different topography and wettability that mimicked the elytra of the beetle were fabricated to study the effect of these factors on fog harvesting. The superhydrophobic bulgy sample harvested 1.5 times the amount of water than the sample with combinational pattern of hydrophilic bulgy/superhydrophobic surrounding and 2.83 times than the superhydrophobic surface without bulge. These bulges focused the droplets around them which endowed droplets with higher velocity and induced the highest dynamic pressure atop them. Superhydrophobicity was beneficial for the departure of harvested water on the surface of sample. The bulgy topography, together with surface wettability, dominated the process of water supply and water removal.

Effect of surface topography and wettability on the Leidenfrost effect.

When deposited on a superheated surface, a droplet can be levitated by its own vapour layer, a phenomenon that is referred to as the Leidenfrost effect. This dynamic effect has attracted interest for many potential applications, such as cooling, drag reduction and drop transport. A lot of effort has been paid to this mechanism over the past two and half centuries. Herein, we not only review the classical theories but also present the most recent theoretical advances in understanding the Leidenfrost effect. We first review the basic theories of the Leidenfrost effect, which mainly focuses on the relationship between the drop shape, vapour layer and lifetime. Then, the shift in the Leidenfrost point realized by fabricating special surface textures is introduced and the mechanisms behind this are analyzed. Furthermore, we present the reasons for the droplet transport in both classical Leidenfrost and pseudo-Leidenfrost regimes. Finally, the promising breakthroughs of the Leidenfrost effect are briefly addressed.