Aerodynamics-assisted, efficient and scalable kirigami fog collectors

Durable Superhydrophobic Surfaces with Self-Generated Wenzel Sites for Efficient Fog Collection

Harvesting freshwater from fog is one of the possible solutions to the global water scarcity crisis. Surfaces with both hydrophobic and hydrophilic regions are extensively employed for this purpose. Nevertheless, the longevity of these surfaces is still constrained by their delicate surface structures. The hydrophilic zones may become damaged or contaminated after repeated use, thereby compromising their effectiveness in fog collection. The preparation of generally applicable durable superhydrophobic coatings with self-generated Wenzel sites is reported here for long-term efficient and stable fog collection. The coatings are prepared by depositing the poly(tannic acid) coating as the primer layer on various substrates, self-assembly of trichlorovinylsilane into staggered silicone nanofilaments, and then thiol-ene click reaction with 1H,1H,2H,2H-perfluorodecanethiol. The coatings demonstrate remarkable static superhydrophobicity, robust impalement resistance, and stable self-generated Wenzel sites for water droplets. Therefore, the fog collection rate (FCR) of the coatings reaches 2.13 g cm-2 h-1 during 192 h continuous fog collection, which is triple that of bare substrate and outperforms most previous studies. Moreover, the systematic experiments and models have revealed that the key factors for achieving high FCR on superhydrophobic coatings are forming condensed droplets ≈1 mm in critical radius and a Wenzel site proportion of 0.3-0.4.

Kirigami enabled reconfigurable three-dimensional evaporator arrays for dynamic solar tracking and high efficiency desalination

A kirigami-engineered composite hydrogel membrane is exploited for the construction of three dimensional (3D) solar-tracking evaporator arrays with outstanding evaporation performance and salt tolerance. The hybrid nanofiber network in the hydrogel membrane offers favorable water transport dynamics combined with excellent structural robustness, which are beneficial for the engineering of 3D dynamic structures. Periodic triangular cuts patterned into the membrane allow formation and reconfiguration of 3D conical arrays controlled by uniaxial stretching. With these structures, the tilt angles of the membrane surface are actively tuned to follow the solar trajectory, leading to a solar evaporation rate ~80% higher than that of static planar devices. Furthermore, the tapered 3D flaps and their micro-structured surfaces are capable of localized salt crystallization for prolonged solar desalination, enabling a stable evaporation rate of 3.4 kg m-2 hour-1 even in saturated brine. This versatile design may facilitate the implementation of solar evaporators for desalination and provide inspirations for other soft functional devices with dynamic 3D configurations.

Improved Fog Collection on a Hybrid Surface with Acylated Cellulose Coating

Fog collection serves as an efficient method to alleviate water scarcity in foggy, water-stressed regions. Recent research has focused on constructing a hybrid surface to enhance fog collection efficiency, with one approach being the prevention of liquid film formation at hydrophilic sites. Inspired by the desert beetle, a coating (10-MCC) made by partially acylating microcrystalline cellulose (MCC) exhibits hydrophilic sites alongside a hydrophobic skeleton enabling rapid droplet capture despite its overall hydrophobicity. The captured droplets quickly coalesce into a large droplet driven by the wetting gradient created by the hydrophobic backbone and hydrophilic sites. To achieve greater fog collection efficiency, a hydrophobic-superhydrophobic hybrid surface is formed by combining a coating of 10-MCC with a superhydrophobic surface. The construction of superhydrophobic surfaces typically involves creating a rough surface with a distinctive structure produced by the anodization technique and modifying it with stearic acid. The superhydrophobic surface exhibits excellent corrosion resistance and mechanical stability. Moreover, the hybrid surface shows high efficiency in fog collection, with a tested maximum efficiency of approximately 1.5092 g/cm2/h, 1.77 times that of the original Al sheets. The results demonstrate a remarkable enhancement in fog collection capacity. Furthermore, this work serves as an inspiration for the low-cost and innovative design of engineered surfaces for efficient fog collection.

Engineering Kirigami Frameworks Toward Real-World Applications

The surge in advanced manufacturing techniques has led to a paradigm shift in the realm of material design from developing completely new chemistry to tailoring geometry within existing materials. Kirigami, evolved from a traditional cultural and artistic craft of cutting and folding, has emerged as a powerful framework that endows simple 2D sheets with unique mechanical, thermal, optical, and acoustic properties, as well as shape-shifting capabilities. Given its flexibility, versatility, and ease of fabrication, there are significant efforts in developing kirigami algorithms to create various architectured materials for a wide range of applications. This review summarizes the fundamental mechanisms that govern the transformation of kirigami structures and elucidates how these mechanisms contribute to their distinctive properties, including high stretchability and adaptability, tunable surface topography, programmable shape morphing, and characteristics of bistability and multistability. It then highlights several promising applications enabled by the unique kirigami designs and concludes with an outlook on the future challenges and perspectives of kirigami-inspired metamaterials toward real-world applications.

A review of the methods of harvesting atmospheric moisture

Moisture is an inherent constituent of air present across the world. The relative humidity varies with the change in temperature and climate specific to a region. In some regions of the world, there may be a relatively inadequate number of grains of moisture in the air in comparison with other regions. These factors widen the scope for the deployment of decentralized technology to capture water. The effectiveness in capturing moisture gains significance in these regions. Among the numerous forms of moisture, fog and dew are studied in depth. Over time, flora and fauna in different ecosystems have adapted to capture moisture as well as repel excesses of it according to their requirements. Therefore, bio-inspired studies and tailored engineering strategies have been incorporated in this review. Since efficient technologies are required at moisture-scarce locations, active moisture harvesting has also been studied. The use of innovative materials along with different energy sources to capture water is elaborated. The effects of climate change and environmental contamination on harvested moisture are therefore assessed. Community participation and economical use of harvested fog or dew influence the sustainability of moisture-capture projects. Therefore, this article also provides an insight into the services of decentralized water-harvesting projects run by diverse organizations and researchers across the globe.

Laser-Textured Hybrid Brass Pattern Array Surface for High-Efficiency Fog Collection

Fog collection holds promise for addressing water shortage. However, the conventional fabrication of fog collection devices, normally chemical methods, suffers many challenges, such as complicated preparation and environmental issues. Herein, we proposed a green fabrication strategy to construct superhydrophobic/hydrophilic surfaces on the brass substrate via the combination of laser fabrication and heat treatment. The wettability of brass is directly dictated by the laser process parameters. The different superhydrophobic/hydrophilic hybrid pattern surface with a rectangular/triangular array was designed for an optimal fog collection performance. The maximum water collection efficiency of the prepared surface is measured up to 427.36 mg h-1 cm-2, which is 97% higher than that of the control sample. Furthermore, the surface can be folded into different forms to realize a flexible collector. We envision that our work provides a green fabrication strategy to construct a superwetting surface for highly efficient fog collection.

Modular design of curved beam-based recyclable architected materials

Advances in manufacturing technologies have enabled architected materials with unprecedented properties. These materials are typically irreversibly designed and fabricated with characteristic geometries and specific mechanical properties, thus rendering them suitable for pre-specified requests. However, these materials cannot be recycled or reconstructed into different shapes and functionalities to economically adapt to various environments. Hence, we present a modular design strategy to create a category of recyclable architected materials comprising elastic initially curved beams and rigid cylindrical magnets. Based on numerical analyses and physical prototypes, we introduce an arc-serpentine curved beam (ASCB) and systematically investigate its mechanical properties. Subsequently, we develop two sets of hierarchical modules for the ASCB, thus expanding the constructable shape of architected materials from regular cuboids to complex curved surfaces. Furthermore, we demonstrate that the magnets attached to the centers of specific serpentine patterns of the modules allows the effective in-situ recycling of the designed materials, including sheet materials for non-damage storage, bulk materials for tunable stiffness, and protective package boxes for reshaping into decorative lampshades. We expect our approach to improve the flexibility of architected materials for multifunctional implementation in resource-limited scenarios.

Kirigami Makes a Soft Magnetic Sheet Crawl

Limbless crawling on land requires breaking symmetry of the friction with the ground and exploiting an actuation mechanism to generate propulsive forces. Here, kirigami cuts are introduced into a soft magnetic sheet that allow to achieve effective crawling of untethered soft robots upon application of a rotating magnetic field. Bidirectional locomotion is achieved under clockwise and counterclockwise rotating magnetic fields with distinct locomotion patterns and crawling speed in forward and backward propulsions. The crawling and deformation profiles of the robot are experimentally characterized and combined with detailed multiphysics numerical simulations to extract locomotion mechanisms in both directions. It is shown that by changing the shape of the cuts and orientation of the magnet the robot can be steered, and if combined with translational motion of the magnet, complex crawling paths are programed. The proposed magnetic kirigami robot offers a simple approach to developing untethered soft robots with programmable motion.

Origami-like 3D Fog Water Harvestor with Hybrid Wettability for Efficient Fog Harvesting

Collecting water in fog has also become a breakthrough to solve the hidden danger of water shortage in some arid areas. The three-dimensional (3D) structure fog collection material can increase the surface area in direct contact with the fog flow and reduce the quick flow of fog, which can effectively improve the fog collection efficiency. Imitating the three-dimensional structure of corrugated paper, the 3D fog collecting material with hybrid wettability was prepared by chemical and physical means. We discuss the influence of different wettability combinations on the fog collection efficiency of 3D structures and study the influence of spraying times and illumination times on the surface wettability during the construction of wettability. We also study the influence of the concavity and tip as well as the bending angle on the fog collection in the 3D structure and obtain the most reasonable concavity and convex ratio and bending angle. The superhydrophilic and superhydrophobic 3D structure fog harvesting material prepared by us performs well in the fog harvesting process, and the fog harvesting efficiency reaches 1.442 g cm-2 h-1. The fog collection efficiency is 418% of the original zinc sheet. At the same time, compared with the superhydrophilic and superhydrophobic hybrid two-dimensional (2D) plane, the increase is 168%, and compared with the superhydrophobic 3D structure, the increase is 150%.

Effect of Wettability and Adhesion Property of Solid Margins on Water Drainage

Liquid flows at the solid surface and drains at the margin under gravity are ubiquitous in our daily lives. Previous research mainly focuses on the effect of substantial margin's wettability on liquid pinning and has proved that hydrophobicity inhibits liquids from overflowing margins while hydrophilicity plays the opposite role. However, the effect of solid margins' adhesion properties and their synergy with wettability on the overflowing behavior of water and resultant drainage behaviors are rarely studied, especially for large-volume water accumulation on the solid surface. Here, we report the solid surfaces with high-adhesion hydrophilic margin and hydrophobic margin stably pin the air-water-solid triple contact lines at the solid bottom and solid margin, respectively, and then drain water faster through stable water channels termed water channel-based drainage over a wide range of water flow rates. The hydrophilic margin promotes the overflowing of water from top to bottom. It constructs a stable "top + margin + bottom" water channel, and a high-adhesion hydrophobic margin inhibits the overflowing from margin to bottom and constructs a stable "top + margin" water channel. The constructed water channels essentially decrease marginal capillary resistances, guide top water onto the bottom or margin, and assist in draining water faster, under which gravity readily overcomes the surface tension resistance. Consequently, the water channel-based drainage mode achieves 5-8 times faster drainage behavior than the no-water channel drainage mode. The theoretical force analysis also predicts the experimental drainage volumes for different drainage modes. Overall, this article reveals marginal adhesion and wettability-dependent drainage modes and provides motivations for drainage plane design and relevant dynamic liquid-solid interaction for various applications.

Patterning Wettability for Open-Surface Fluidic Manipulation: Fundamentals and Applications

Effective manipulation of liquids on open surfaces without external energy input is indispensable for the advancement of point-of-care diagnostic devices. Open-surface microfluidics has the potential to benefit health care, especially in the developing world. This review highlights the prospects for harnessing capillary forces on surface-microfluidic platforms, chiefly by inducing smooth gradients or sharp steps of wettability on substrates, to elicit passive liquid transport and higher-order fluidic manipulations without off-the-chip energy sources. A broad spectrum of the recent progress in the emerging field of passive surface microfluidics is highlighted, and its promise for developing facile, low-cost, easy-to-operate microfluidic devices is discussed in light of recent applications, not only in the domain of biomedical microfluidics but also in the general areas of energy and water conservation.

Light‐ and Field‐Controlled Diffusion, Ejection, Flow and Collection of Liquid at a Nanoporous Liquid Crystal Membrane

Liquid manipulation at solid surfaces has attracted plenty of interest yet most of them are limited to one or two direction(s), while transport in three dimensions is largely unexplored. Here, we demonstrate three‐dimensionally steered dynamic liquid mobility at nanoporous liquid crystal polymer coatings. To this end, we orchestrate liquid motion via sequential triggers of light and/or electric field. Upon a primary flood exposure to UV light, liquid is ejected globally over the entire coating surfaces. We further reallocate the secreted liquid by applying a secondary electric field stimulus. By doing so, the liquid is transported and collected at pre‐set positions as determined by the electrode positions. We further monitor this process in real‐time and perform precise analysis. Interestingly, when applying those two triggers simultaneously, we discover a UV‐gated liquid‐release effect, which decreases threshold voltage as well as threshold frequency.

Recent Development of Atmospheric Water Harvesting Materials: A Review

The lack of freshwater has been threatening many people who are living in Africa, the Middle East, and Oceania, while the discovery of freshwater harvesting technology is considered a promising solution. Recent advances in structured surface materials, metal-organic frameworks, hygroscopic inorganic compounds (and derivative materials), and functional hydrogels have demonstrated their potential as platform technologies for atmospheric water (i.e., supersaturated fog and unsaturated water) harvesting due to their cheap price, zero second energy requirement, high water capture capacity, and easy installation and operation compared with traditional water harvesting methods, such as long-distance water transportation, seawater desalination, and electrical dew collection devices in rural areas or individual-scale emergent usage. In this contribution, we highlight recent developments in functional materials for "passive" atmospheric water harvesting application, focusing on the structure-property relationship (SPR) to illustrate the transport mechanism of water capture and release. We also discuss technical challenges in the practical applications of the water harvesting materials, including low adaptability in a harsh environment, low capacity under low humidity, self-desorption, and insufficient solar-thermal conversion. Finally, we provide insightful perspectives on the design and fabrication of atmospheric water harvesting materials.

Unclogged Janus Mesh for Fog Harvesting

Janus membranes with asymmetric surface wettability have been extensively utilized in various fields, including fog harvesting, because of their novel liquid transport properties. However, Janus membranes have an inherent disadvantage in terms of aerodynamic efficiency in harvesting fog because of the clogged water bridges caused by the small pore size. In the present work, we applied Janus wettability to mesh geometry with systematically varying hole sizes. For a clogged mesh with a small hole size, capillary water transport to the mesh back via the wettability gradient in the direction of fog flow helps harvest more fog by enhancing water drainage, similarly to the Janus membrane. The advantage of the capillary water transport extends to a clog-free mesh with larger hole sizes but more preferably to a Janus mesh with a superhydrophilic back, which presents the highest level of fog-harvesting yield because of the fast shedding frequency and short onset time. In contrast, a Janus mesh with a superhydrophobic front, which also has a wettability gradient along the fog flow, produces a lower fog-harvesting performance, particularly at slow fog speeds, because of the dropwise deposition of large water drops that locally disturb fog flow around a protruding water surface. On the other hand, the other type of Janus mesh with a superhydrophilic front is observed to minimize this disadvantage in the local fog flow by virtue of the filmwise deposition. It is also found that some Janus treatments can help protect mesh holes from clogging up by either forming a thin water meniscus or resisting water transport through the mesh holes.

Topological alternation from structurally adaptable to mechanically stable crosslinked polymer

Stimuli-responsive polymers with complicated but controllable shape-morphing behaviors are critically desirable in several engineering fields. Among the various shape-morphing materials, cross-linked polymers with exchangeable bonds in dynamic network topology can undergo on-demand geometric change via solid-state plasticity while maintaining the advantageous properties of cross-linked polymers. However, these dynamic polymers are susceptible to creep deformation that results in their dimensional instability, a highly undesirable drawback that limits their service longevity and applications. Inspired by the natural ice strategy, which realizes creep reduction using crystal structure transformation, we evaluate a dynamic cross-linked polymer with tunable creep behavior through topological alternation. This alternation mechanism uses the thermally triggered disulfide-ene reaction to convert the network topology - from dynamic to static - in a polymerized bulk material. Thus, such a dynamic polymer can exhibit topological rearrangement for thermal plasticity at 130°C to resemble typical dynamic cross-linked polymers. Following the topological alternation at 180°C, the formation of a static topology reduces creep deformation by more than 85% in the same polymer. Owing to temperature-dependent selectivity, our cross-linked polymer exhibits a shape-morphing ability while enhancing its creep resistance for dimensional stability and service longevity after sequentially topological alternation. Our design enriches the design of dynamic covalent polymers, which potentially expands their utility in fabricating geometrically sophisticated multifunctional devices.