Fog Capture Research Articles

Nanotree array textured lubricant-infused frame for efficient fog harvesting

Owing to its passive collection, low cost and little energy consumption, fog harvesting is a sustainable technology to obtain fresh water resources. Inspired by creatures, surfaces with unique wettability are prepared, especially the lubricant-infused surface have drawn immense attention in recent years. The lubricant-infused surface, however, tends to be unstable, losing control over the fog capture and droplet movement. In this work, nanotree array textured lubricant-infused frame (LIF) was prepared. Notably, due to the cooperation of the fine micro/nanostructure and covalent bond Zn−O−Si between lubricant and substrate, the lubricant retention capacity was enhanced. Under hostile conditions, such as high-speed centrifugation, long-term storage, acidic solution and high temperature environment, the slippery surface still display excellent stability. Furthermore, the slippery surface exhibited high fog harvesting efficiency, about 85% higher fog harvesting efficiency compared to the original surface. Therefore, the lubricant-infused frame is promising for practical applications.

Speculative relations in Lima

This article draws on two examples of encounters with the limits of fog capture in Lima to frame limitations as creative resources for ethnographic inquiry. In both examples, fog capture rendered speculatively conceivable previously backgrounded urban and ecological (dis)connections to residents on the city’s periphery, including the possibility to envisage certain relational reconfigurations. By analogously framing these experimental effects as one potential outcome of ethnographic practice, the article locates the kernel of such outcomes in the inescapability of limitations. This not only acknowledges the many obstructions and exclusions inherent to anthropological research, but taps into them as that which might allow for fieldwork encounters to properly bear on theory and analysis. Rather than things to avoid or overcome, I argue that limits by and of themselves have the capacity to suspend and modify abstractions and the course of events.

Fog Harvesting Devices Inspired from Single to Multiple Creatures: Current Progress and Future Perspective

AbstractThe increasing demand for clean water driven by the rapid growth of the population and the pollution of water necessitates the development of direct and rapid water harvesting methods. Fog harvesting is proven as a highly efficient water capture method in dry but foggy areas. Herein, the state‐of‐the‐art developments on the multiple biomimetic fog harvesting devices (FHDs) are presented. First, the fundamental and specific mechanisms of fog harvesting involving the Namib Desert beetle, spider silk, cactus, and Nepenthes alata are described in detail, respectively. Second, an in‐depth discussion on the mechanisms of fog harvesting including fog capture and water transport is proposed. Third, a detailed account of the innovative design strategies and fabrication technologies of FHDs is proposed, from single to multiple biomimetic FHDs with typical examples and the merits and demerits are compared. Finally, a critical analysis of current challenges and future development is presented, aiming to promote next‐generation FHDs from scientific research to practical application.

Superhydrophilic-Superhydrophobic Multifunctional Janus Foam Fabrication Using a Spatially Shaped Femtosecond Laser for Fog Collection and Detection.

Fog collection is an effective method for addressing water shortages in arid areas. By constructing a Janus structure with asymmetric wettability on its two sides, flexible and efficient fog capture can be achieved. However, in situ detection and fog collection on a Janus surface are still challenging tasks. Herein, a novel method for producing a superhydrophilic-superhydrophobic Janus fog collector is proposed; the method utilizes a combined process in which a spatially shaped femtosecond laser treatment (superhydrophilic) is applied to one side of a copper foam and a chemical replacement reaction (superhydrophobic) is applied to the other side of the copper foam. Two configurations of the Janus structure were designed to study different water transport behaviors. Furthermore, the Au micro-nanoparticle prepared adhered to the Janus structure, indicating the effectiveness of surface-enhanced Raman spectroscopy detection. The Janus foam shows excellent sensitivity and stability on testing the fog mixed with rhodamine 6G. This surface allows for the simultaneous collection and detection of fog, which can provide insights into the preparation of Janus multifunction structures and how such structures can play a key role in the subsequent purification and usage of water resources.

Ecology of Capture: Creating Land Titles Out of Thin Air in Coastal Peru

ABSTRACT In coastal Peru, fog has recently been re-apprehended as an alternative water source for residents on the urban periphery. This article describes how a local NGO’s fog capture project repurposed its multi-national big tech funder into an engine of informal urbanisation. I demonstrate how by instigating a process of multi-directional capture between NGO, funder, government, and recipients, the NGO’s fog catchers mediated their beneficiaries’ hopes about the acquirement of land titles, thereby drawing the state in as a potential supplier of the very infrastructure to which fog capture was being presented as an alternative. Against this backdrop, I propose an approach to micro-infrastructures as political materials with the capacity to reconfigure sociopolitical realities.

A Quadruple-Biomimetic surface for spontaneous and efficient fog harvesting

Rational manipulation of liquid motion on functional surfaces are of high interest for the fabrication of advanced water-harvest devices. Great efforts have dedicated to the improvement of water condensation, coalescence and transportation in previous works, allowing efficient fog capture and droplet motion. However, the collection barrier greatly deciding water collection performance has rarely been concerned. Learning from unique skills of multiple creatures, we design to construct and optimize superhydrophilic patterns on slippery surfaces. Such patterned slippery-superhydrophilic surfaces are capable of effectively nucleating water droplets by the superhydrophilic arrays, promoting droplet coalescence and delivery with the wedge structure and slippery feature, and reducing collection barrier with the nephrolepis auriculata-like architecture. Notably, the spontaneously water-harvest system presents water collection efficiency of 2166 ± 71 mg cm-2h−1 that is improved by 139% compared with that of slippery surface. The multi-inspired strategy regarding the synergistical optimization of the whole harvesting process brings new opportunities to environmental and energy applications.

Near-bulge oil meniscus-induced migration and condensation of droplets for water collection: Energy saving, generalization and recyclability

It should be noted that the multifunctional surface is ideal for manipulation droplets to play different roles in various fields, especially for water collection. Here, a unique design scheme, a multibioinspired slippery surface for water collection, is proposed derived from the Namib desert beetle, cactus, aquatic vegetations and Nepenthes, which synergistically combines fog capture, condensation and transportation, indicating better performance than other synthetic surfaces. Without relying on additional energy input or droplet coalescence, this multi-bioinspired slippery surface shows ideal droplet pumping and water collection efficiency. Moreover, the morphology of the triple contact lines is simulated by Surface Evolver, and the state of droplet’s migration is discussed from the perspective of force analysis and energy calculation. The experimental results show that the as-prepared substrate had excellent stability and weather resistance under different circumstance. Compared with the single original Zn sheet, the water collection efficiency of this unique water collection device is increased by about 257.9%. Therefore, this reasonable design strategy and the corresponding theoretical simulation can be applied to a wide range of water harvesting and other fields.

The (ontological) politics of fog capture in Lima, Peru

Fog oasis conservationists in Lima attend to fog as a material possibility for capturing and enfolding in infrastructures of reforestation. Yet, their efforts become deliberately obstructed by the informal squatters whom conservationists perceive to threaten these ecosystems. Fog capture thus raises questions not only about the relation between infrastructure and environment but also the urban inequalities that must be addressed for such more‐than‐human relations to become differently configured.

Bioinspired Nanofibril-Humped Fibers with Strong Capillary Channels for Fog Capture.

Bioinspired nanofibril-humped fibers (BNFs) are fabricated by using thermoplastic polyester elastomer and chitosan, via combining the electrospinning technique and fluid coating method to achieve periodic humps composed of interlaced random nanofibrils and a joint composed of aligned nanofibrils, which are highly similar to the micro/nanostructures of wetted spider silk. Especially, nanofibrils can increase the specific area of the hump to capture fog droplets effectively and transport water in channels between the nanofibrils under humid conditions, and thus the fog droplets can coalesce and be highly efficiently transported toward humps for water collection directionally. Such an ability of highly efficient fog capture is attributed to cooperation of an efficient transportation inside the outer shell of BNFs and outside transportation. Inside transportation is induced by anisotropic capillary channels between nanofibrils. When BNFs are wetted, the inside transportation mode is dominated for water collection, induced by anisotropic capillary channels between nanofibrils. BNF web is also used to investigate the droplet transportation in different cross-fiber contact modes in the process of fog capture on a large scale. This study offers an insight into the design of novel materials, which is expected to be developed for some realms of applications, such as fog harvesting engineering, filtration, and others.

A Bioinspired Slippery Surface with Stable Lubricant Impregnation for Efficient Water Harvesting.

Inspired by Nepenthes pitcher plants, slippery liquid-infused porous surfaces (SLIPS) have recently attracted increasing attention for directional transport and movement manipulation of water droplets. Nevertheless, infused lubricants are generally instable and easy to deviate from such surfaces during applications, resulting in the lost control on the fog capture and motion of droplets as well as serious risk of water safety. Here, a highly stable SLIPS with improved lubricant storage is developed through the structure design of synergistically constructing regular micro-pincushion and nanoparticles. Notably, on the basis of the microstructure, the presence of nano-architecture shows great contribution to obviously increased capillary force as well as suppressed lubricant loss during water collection. Featuring the stable surface-slippery property, the biomimetic SLIPS displays well maintained dropwise coalescence of water from fog and efficient water harvesting performance. The water collection efficiency is as high as 852 mg cm-2 h-1 and is stable within continuous 20 h application. This fundamental illustration of structural synergism can be further applied to construct more new water manipulation and harvesting platforms with stably slippery surfaces/interfaces.

Sensitivity of a tropical montane cloud forest to climate change, present, past and future: Mt. Marsabit, N. Kenya

During the Last Glacial Maximum (LGM) lowland forests contracted throughout the tropics but, by contrast, many montane forest taxa moved to lower elevations. These taxa are often found in cloud forests, which are globally important ecosystems that depend on the capture of atmospheric water from fog drifting through the canopy, here referred to as occult precipitation. Understanding the response of tropical montane taxa to climate variations is limited by a lack of modern data on fog capture; whereas palaeoecological data only provide indirect evidence for its importance. Hence, the response of vegetation to fog capture is not considered in palaeo-estimates of precipitation. We develop a method that uses satellite Normalized Difference Vegetation Index (NDVI) data to estimate the annual amount of occult precipitation and investigate the sensitivity of a cloud forest to past and future changes in both rainfall and occult precipitation. We apply this method using satellite and meteorological data from 1982 to 2015 collected at Mt Marsabit, which is located in northern Kenya (2.34∘ N, 37.97∘ E, summit 1707 m a.s.l.). Mt Marsabit has a sub-humid tropical montane cloud forest at its summit that is excessively green for the amount of rain it receives. We estimate the annual amount of occult precipitation for current conditions at about 900 mm y−1 which is more than the average annual rainfall of 700 mm y−1. This is consistent with the observation that, for the wider Marsabit area, interannual variations in NDVI are more closely linked to changes in cloud-base height (r2=0.87) than to changes in rainfall (r2=0.67). We investigate the sensitivity of forest extent to past and future changes; for the LGM we estimate that cloud-base height decreased by 500 m in response to a 4 ∘C cooling and that this caused a 20%–100% increase in forest area despite a 30% decrease in rainfall, a 22% decrease in atmospheric humidity and a substantial reduction of atmospheric CO2 levels (values representative for mountains in Kenya during the LGM). An expected increase of 250 m in the cloud-base height associated with a future 2 ∘C global warming is likely to reduce forest extent by 50%–100%. Our results indicate that the satellite vegetation record is useful to estimate modern hydrological inputs into drier cloud forests (up to 2000 mm y−1) and that this information can be used to estimate the contribution of occult precipitation to altitudinal displacements of tropical montane cloud-forest species during the Quaternary.

Medium, Vector, and Connector: Fog and the Maintenance of Ecosystems

Fog and low-lying cloud (fog) play a significant role in the maintenance of ecosystems, from desert to alpine and from coastal to inland systems. Our central thesis is that fog provides ecosystems with critical water and nutrient subsidies, and also delivers pollutants, that often control ecosystem function. Fog is a medium, vector, and connector. In this mini-review, we synthesize recent research advances that reveal the diverse ways that fog shapes ecosystem processes. Crown wetting, elemental deposition, and light scattering and absorption are fundamental mechanisms by which fog has been shown to influence water fluxes, productivity, and decomposition in hyper-arid to ever-wet regions. These impacts are ultimately mediated by the structure and composition of biological systems that allow fog capture and utilization of resource subsidies. Climate change, and changes in land use, ocean circulation, and atmospheric pollution are simultaneously altering the nature of fog itself, and the architecture of the ecosystems adapted to capture it. The coupling between atmosphere and biosphere in fog-enshrouded areas raises new questions about past and future fog-dominated ecosystems, and their maintenance and diversity, in the face of global change.

Onset time of fog collection.

Fog collection is a promising solution to the worldwide water scarcity problem and is also of vital importance to industrial processes, such as recapturing water in cooling towers and mist elimination. To date, numerous studies have investigated the fog collection rate, a parameter that denotes the average performance over a long period of time. However, the initial period (referred to as onset time) between the start of the fog-laden flow and the actual collection of the captured liquid (a delay in time caused by droplet growth to a critical weight that exceeds droplet-surface retention force) has not been systematically understood. A longer onset time may result in a more serious clogging issue that deteriorates the collection rate and, hence, understanding this phenomenon is important. Here, we study how the onset time is determined by the capture and transport of fog using individual, vertical wires with various surface wettabilities and diameters, under different wind speeds. This approach allows us to derive a scaling law that correlates the onset time with the fog capture process and droplet-surface retention force, governed by aerodynamics and interfacial phenomena, respectively. In particular, the onset time decreases with an increasing rate of fog capture or a decreasing droplet-surface retention force. This study introduces an important aspect in the evaluation of fog collection and provides insights for the optimal design of fog collectors and mist eliminators.

Regeneration and Expansion of Quercus tomentella (Island Oak) Groves on Santa Rosa Island

Quercus tomentella (island oak) is an endemic species that plays a key functional role in Channel Island ecosystems. Growing in groves on highland ridges, Q. tomentella captures fog and increases water inputs, stabilizes soils, and provides habitat for flora and fauna. This cloud forest system has been impacted by a long history of ranching, and restoration efforts are underway that include erosion control, leaf litter capture, fog capture, and reforestation. To inform retoration efforts, we explored tree regeneration and the potential for Q. tomentella grove expansion on Santa Rosa Island. We delineated current and historic groves at Black Mountain by comparing stand maps from 1989 and aerial photographs from 1994 and 2015. We evaluated regeneration in the outlying areas by recording the location, diameter at breast height, number of trunks, height class, percent crown mortality, nurse plant species (if present), and reproductive status for all 4355 outlying seedlings, saplings, and mature trees. We defined outliers as individuals that were 15 m outside of the canopy of island oak groves. There are 14 groves at Black Mountain, and grove size expanded by an average of 36.9% (SD 18.5%) between 1994 and 2015. Nurse plants correlated positively with outlier tree height and reduced percent crown mortality. This effect is potentially due to increased fog drip from nurse plant species such as Quercus pacifica (island scrub oak), Heteromeles arbutifolia (toyon), and Baccharis pilularis (coyote brush). These results indicate that Q. tomentella is regenerating and that nurse plants can serve as catalysts for ecosystem restoration.

The Influence of Slope on Vegetation Recovery Following Nonnative Grazer Removal on Santa Rosa Island, California

Ecosystem restoration efforts have been ongoing on the Channel Islands of California since the 1980s. Although these island ecosystems evolved without ungulate grazers, large nonnative grazers, including sheep, cattle, feral pigs, deer, and elk, were present on the islands for over 160 years. Intensive grazing led to reductions in the extent of woody vegetation, increases in the area of grassland and bare ground, and widespread landsliding and gully erosion. This study focuses on Santa Rosa Island, the second largest (215.3 km2) island in Channel Islands National Park. After the park was created in 1980, the National Park Service progressively removed nonnative grazers to facilitate the restoration of native vegetation and the wildlife communities they support. We constructed a time series (1989 to 2015) of Landsat TM5 and Landsat 7 ETM+ images to evaluate large-scale and long-term vegetation change in response to grazer removal on Santa Rosa Island. We also evaluated the influence of slope percent, which can be an indicator of past grazing accessibility, on ecosystem recovery. Results indicate that removing nonnative grazers led to passive restoration of 42.1 km2 of scrub, chaparral, and woodland vegetation. In contrast, the area of grassland vegetation decreased by 31.2 km2 and bare ground decreased by 12.0 km2. The extent of scrub and woodland vegetation recovery was greater on gentle and moderate slopes compared to steep slopes, indicating that terrain does influence passive restoration. Despite changes in vegetation cover, 5.4 km2 has remained bare. Much of the bare ground is on ridgelines that were denuded down to the bedrock or regolith. Active restoration will be necessary on bare ridgelines, such as erosion control, fog capture, and oak woodland reforestation.

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.

Superfast Liquid Transfer Strategy Through Sliding on a Liquid Membrane Inspired from Scorpion Setae

AbstractAlthough diversified biological structures have evolved fog collection abilities, the typical speeds of the condensed water droplets on these surfaces are too slow to have practical utility. The main challenge focuses on the elimination of the interfacial hydrodynamic resistance without external energy support. Here, an unusual strategy for superfast self‐support transfer condensed droplets is supported by sliding on seta of desert scorpion. It can be rapidly wetted by the fog droplets owing to its conical shape with linear gradient channels. A loss of interfacial resistance by this hydrodynamically lubricating water membrane could significantly accelerate the movement of the droplets, thus making its velocity increasing by one order of magnitude, or even more. Inspired by this novel strategy, the novel bioinspired materials are fabricated with the similar gradient channel structures and droplet transportation mode, which can make the condensed droplets spontaneously slide on the low‐friction liquid membrane. The fundamental understanding of superfast fog capture and the sliding dynamics of condensed droplets in this system could inspire to develop novel materials or various systems to transfer liquid fast and efficiently without external energy support.

Fog collection on a conical copper wire: effect of fog flow velocity and surface morphology

The conical copper wires (CCWs) were subjected to alkali assistant oxidation or electrochemical deposition to form superhydrophilic wettability of ∼4° with needle-like or leaf-like morphology, respectively. The superhydrophobic CCWs with water contact angles of ∼156° were further constructed by modification with 1-dodecanethiol. The CCWs were used to study the effect of fog flow velocity and surface morphology on fog collection. With the fog flow velocity increased, the dominant factor for fog collection changed from fog capture to droplet motion. The surfaces with needle-like morphology displayed better fog capture ability while the surfaces with leaf-like morphology were more prone to driving droplet motion.

Bioinspired fog capture and channel mechanism based on the arid climate plant Salsola crassa

Salsola crassa plant hairs collect fog in their natural arid climate habitat through the capture and growth of water droplets. These then, either drip onto the ground below due to gravity, or coalesce into larger attached water droplets, whilst concurrently rolling downwards along the curvature of the Salsola crassa leaf (fog collection and water channelling mechanism). Non-woven and cotton fibrous materials are shown to mimic the fog harvesting behaviour of Salsola crassa hairs, where the overall mist collection efficiency can be enhanced by over 300 percent through the incorporation of multiple length scale (hierarchical) channel structures in conjunction with hydrophobic surface functionalisation.

Active Antifogging Property of Monolayer SiO2 Film with Bioinspired Multiscale Hierarchical Pagoda Structures.

Antifogging surfaces with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, a major challenge remains in achieving high-speed antifogging performance and revealing the hydrophilic-based antifogging mechanism of glass or other transparent materials under aggressive fogging conditions. Herein, with inspiration from the fog-free property of the typical Morpho menelaus terrestris butterfly (Butler, 1866) wing scales, a monolayer SiO2 film with multiscale hierarchical pagoda structures (MHPSs) based on glass substrate was designed and fabricated using an optimized biotemplate-assisted wet chemical method without any post-treatments. The biomimetic monolayer film (BMF) composed of nanoscale SiO2 3D networks displayed excellent antifogging properties, which is superior to that of the glass substrate itself. The MHPS-based BMF even kept high transmittance (∼95%) under aggressive fog conditions, and it almost instantaneously recovered to a fog-free state (<5 s). Moreover, the underlying active antifogging strategy gathering initial fog capture and final antifog together was revealed. The fogdrops spontaneously adhered on the BMF surface and rapidly spread along the MHPSs in an anisotropic way, which made the fogdrops evaporate instantaneously to attain an initial fog-free state, leading to an efficient active antifogging performance. These properties mainly benefit from the synergistic effect of both hydrophilic chemical compositions (nanoscale SiO2) and physical structures (biomimetic MHPSs) of the BMF. High-speed active antifogging performance of the glass materials enabled the retention of a high transmittance property even in humid conditions, heralding reliable optical performance in outdoor practical applications, especially in aggressive foggy environments. More importantly, the investigations in this work offer a promising way to handily design and fabricate quasi-textured surfaces with multiscale hierarchical structures that possess high-performance physicochemical properties.