Three-Dimensional Multilayer Vertical Filament Meshes for Enhancing Efficiency in Fog Water Harvesting

Abstract

Novel types of vertical filament mesh (VFM) fog harvesters, 3D VFM fog harvesters, and multilayer 3D VFM fog harvesters were developed by mimicking the water-harvesting nature of desert beetles and the spider silks from fog. Four different types of polymer filaments with different hydrophilic–hydrophobic properties were used. The polymer filaments were modified with the polyurethane–sodium alginate (PU–SA) mixture solution, and a simple spraying method was used to form alternating 3D PU–SA microbumps. Polymer VFMs exhibited a higher fog-harvesting efficiency than the vertical metal meshes. Moreover, the hydrophobic VFM was more efficient in fog harvesting than the hydrophilic VFM. Notably, the fog-harvesting efficiency of all VFMs increased by 30–80% after spraying with the mixed PU–SA solution to form a 3D geometric surface structure (3D PU–SA microbumps), which mimicked the desert beetle back surface. This modification caused the fog-harvesting efficiency of PTFE 3D VFM to be thrice higher than that of Fe VFM. This increase was attributed to the improved synergistic effects of fog capturing, droplet growing, and droplet shedding. The multilayer VFMs were more efficient in fog harvesting than the single-layer VFMs because of a larger droplet capture area. The fog-harvesting efficiency of two-layer and four-layer polymer VFMs was approximately 35% and about 45% higher than that of the single-layer polymer VFMs, respectively. The four-layer PTFE 3D VFM with the type B PU–SA bump surface (bump/PU–SA) had the highest efficiency of 287.6 mL/m2/h. Besides the high fog-harvesting efficiency, the proposed polymer VFMs are highly stable, cost-effective, rust-free, and easy to install in practical applications. These advantages are ascribed to the elasticity of the polymer filaments. This work provides new ideas and methods for developing high-performance fog harvesters such as the 3D VFM.

Enhancing Fog Harvest Efficiency by 3D Filament Tree and Elastic Space Fabric

“…A thin film easily formed on the filament surface, leading to a decrease in droplet capturing areas (ability condensation). 29 Figures 3a1−d1 and S13 (Supplementary Discussion 8) show the simulated filament clusters (modified filament surface similar to A-Tree 3D@SF, B-Tree 3D@SF, C-Tree 3D@SF and 3D@SF). Droplet shapes on the surfaces of highly hydrophobic filaments of A-Tree 3D@SF and B-Tree 3D@SF were more rounded compared to those on the C-Tree 3D@SF and 3D@SF surfaces.…”

“…This is positive for quick formation of large droplets on the filament surface at the bump area (Figures 2a, 5c, and 5e). The F Laplace force is based on eq 1: 29,58…”

“…However, the water harvesting rate was lower than those at 180 and 300 s. If the fog had not condensed into an optimal droplet volume on the filament (droplets are quickly removed), it could have caused the reduction in the fog capture area. 29 Establishing a new droplet formation cycle may take a long time. The stop time of press−relax may coincide with stage 1 and early stage 2.…”

3D-printed spider-web structures for highly efficient water collection

“…Fog is a natural freshwater resource, and it is difficult to capture and use, which limits people's research [ 2 , 3 , 4 ]. There are many creatures in nature that have interesting structures to collect and transport moisture in the moist air, such as the back of a desert beetle with a hydrophilic-hydrophobic mixed mode, cactus spines with a multi-directional branching structure also show the ability to collect fog water, and spider webs also has the amazing ability to collect micro-droplets and be able to guide the automatic transmission of the micro-droplets [ 5 , 6 , 7 , 8 , 9 ]. The researchers found that there are periodically arranged spindle structures on the spider silk.…”

Bioinspired nanoscale hierarchical pillars for extreme superhydrophobicity and wide angular transmittance

“…Hierarchical structures are effective in realizing smart biological behavior in nature by implementing or reinforcing various surface functionalities, such as self-cleaning, antireection, antibiofouling, water harvesting, structural color, and drag reduction. 1,2 These amazing properties enabled by hierarchical structures can be observed in the lotus leaf, [3][4][5][6] pitcher plant, [7][8][9][10][11] moth eye, [12][13][14][15][16] buttery wings, 17 cicada wings, 18 Namib desert beetle's back, [19][20][21] and shark skin. [22][23][24][25] In particular, the introduction of a hierarchical nanostructure on transparent surfaces can lead to signicant performance enhancement for the developing applications such as the cover glass of photovoltaics, building and car windows and lenses of optical sensors.…”