Namib Desert Beetle Research Articles

Biomimetic Superhydrophobic Triboelectric Surface Prepared by Interfacial Self‐Assembly for Water Harvesting

AbstractExtracting water from air offers a promising route to address the global challenge of water scarcity. However, bionic engineering surfaces for water harvesting often struggle with efficiently coordinating droplet nucleation and desorption. The recently emerging triboelectric effect at the liquid–solid interface offers a novel approach for developing bionic fog harvesting surfaces. In this study, inspired by Namib Desert beetles and lotus leaves, a biomimetic superhydrophobic surface with nanoscale hydrophilic domains is prepared via interfacial self‐assembly, exhibiting heterogeneous wettability for effective water harvesting. The essence of interfacial self‐assembly lies in the synergy of non‐covalent interaction forces, driving the self‐assembly of nanoparticles into surface micro‐nano hierarchical structures, thereby regulating wettability and increasing potential nucleation sites. Additionally, the triboelectric effect can directly utilize the triboelectric charges to facilitate droplet migration. The triboelectric effect can be generated by flexible mechanical input induced by walking, which enhances interfacial mass transfer, thereby rapidly improving droplet removal and achieving a 39.02% increase in water harvesting efficiency. This study has opened up a new breakthrough for the design of portable and efficient water harvesting systems.

Diatoms Inspired Green Janus Fabric for Efficient Fog Harvesting

AbstractFog harvesting is a promising path against the global freshwater scarcity. Asymmetric wettability fabric‐based fog collection materials inspired by the Namib desert beetle have been reported widely due to their easy access and adjustable structures. Nevertheless, the single drive force for water transportation produced by the asymmetric wettability is insufficient, causing a non‐ideal fog harvesting efficiency. Moreover, sustainability challenges persist for fog collection materials, primarily due to their heavy dependence on chemical treatments. Herein, a diatom‐inspired Janus fabric (Ly/Csp‐3) based on asymmetric wettability and aperture gradient is developed without additional physical or chemical treatment. The wettability gradient and aperture gradient generate dual directional drive forces that regulate the water transport direction more accurately and enhance the transportation rate more effectively. Ly/Csp‐3 reaches a one‐way transport index of 390.7% and a water collecting rate (WCR) of 1170.5 mg cm−2 h−1, while exhibiting the capability of anti‐acid rain and the resistance to sunlight. This work provides an efficient and programmable biomimetic design proposal for fibrous fog harvesting devices.

Biomimetic Fog Collector with Hybrid and Gradient Wettabilities.

Water scarcity is a global problem and collecting water from the air is a viable solution to this crisis. Inspired by Namib Desert beetle, leaf venation and spider silk, we designed an integrated biomimetic system with hybrid wettability and wettability gradient. The hybrid hydrophilic-hydrophobic wettability design that bionomics desert beetle's back can construct a three-dimensional topography with a water layer on the surface, expanding the contact area with the fog flow and thus improving the droplet trapping efficiency. The venation-like structure with wettability gradient not only provides a planned path for water transportation, but also accelerates water removal under the synergistic effect of gravity and wettability driving force, thus further improving the surface regeneration rate. The collector combines droplet capture, coalescence, transportation, separation, and storage capabilities, which provides new ideas for the design of future high-efficiency fog collectors.

In Situ Collection and SERS Detection of Nitrite in Exhalations on Facemasks Based on Wettability Differences.

As one of the common carriers of biological information, along with human urine specimens and blood, exhaled breath condensate (EBC) carries reliable and rich information about the body's metabolism to track human physiological normal/abnormal states and environmental exposures. What is more, EBC has gained extensive attention because of the convenient and nondestructive sampling. Facemasks, which act as a physical filter barrier between human exhaled breath and inhaled substances from the external environment, are safe, noninvasive, and economic devices for direct sampling of human exhaled breath and inhaled substances. Inspired by the ability of fog collection of Namib desert beetle, a strategy for in situ collecting and detecting EBC with surface-enhanced Raman scattering is illustrated. Based on the intrinsic and unique wettability differences between the squares and the surrounding area of the pattern on facemasks, the hydrophilic squares can capture exhaled droplets and spontaneously enrich the analytes and silver nanocubes (AgNCs), resulting in good repeatability in situ detection. Using R6G as the probe molecule, the minimal detectable concentration can reach as low as 10-16 M, and the relative standard deviation is less than 7%. This proves that this strategy can achieve high detection sensitivity and high detection repeatability. Meanwhile, this strategy is applicable for portable nitrite analysis in EBC and may provide an inspiration for monitoring other biomarkers in EBC.

Patterned Quasi‐Liquid Surfaces for Condensation of Low Surface Tension Fluids

AbstractExtensive research concerns dropwise condensation of low surface tension fluids to promote energy efficiency and decarbonization in thermal energy systems. However, it is challenging as these fluids typically result in filmwise condensation. Drawing inspiration from the Namib desert beetle that enhances condensation through patterned wettability, conventional beetle‐inspired surfaces excel in water condensation but flood when condensing low surface tension fluids. In this work, a patterned quasi‐liquid surface is reported that achieves exceptional dropwise condensation of low surface tension fluids. The surface consists of alternating stripes with low surface energy, that is, a perfluoropolyether (PFPE) and fluorinated quasi‐liquid surface (FQLS), that shows ultralow contact angle hysteresis for ethanol and hexane. The PFPE stripes are slightly more slippery, acting as slippery bridges that accelerate droplet coalescence and removal. It is experimentally demonstrated that the striped PFPE‐FQLS pattern exhibits a heat transfer coefficient 85%, 330%, and 550% higher than that of PFPE, fluorinated silane, and filmwise condensation, respectively. This study reveals that a high contact angle is desired to sustain dropwise condensation, irrespective of contact angle hysteresis. These findings provide a new paradigm for promoting the dropwise condensation of low surface tension fluids and offer valuable insights into surface design for energy sustainability.

Enhancing gas film stability by alternating superhydrophobic and hydrophobic surfaces for stable drag reduction

Superhydrophobic surfaces can significantly reduce the resistance of underwater vehicles, but as the speed increases, the gas film is prone to be destroyed, leading to a decrease in the drag reduction effect or even an increase in the drag. Therefore, enhancing the stability of the gas film is crucial for maintaining the drag reduction effect. Inspired by the honeycomb array pit structures, the high adhesion hydrophobic properties of rose petals, and the wetting gradient surface of Namib desert beetles, an alternating superhydrophobic and hydrophobic surface (ASHHs) was constructed by femtosecond laser to enhance the stability of the gas film. The high adhesion hydrophobic surface (HAHs) provides greater adhesive force, allowing the gas film to firmly pin at the junction of a low-adhesion superhydrophobic surface (LASHs) and HAHs, thereby enhancing the stability of the gas film. The critical failure velocity of ASHHs can reach 2.3 m/s, which is significantly greater than that of low-adhesion superhydrophobic surface samples (LASH-S) (1.7 m/s). ASHHs maintains a stable drag reduction effect of 37% at a velocity of 2.3 m/s, while that of LASH-S is only 6%. It is envisioned that such superhydrophobic surfaces that enhance gas film stability should find widespread applications in minimizing resistance and reducing energy consumption in the marine engineering field.

Geometry for low-inertia aerosol capture: Lessons from fog-basking beetles.

Water in the form of windborne fog droplets supports life in many coastal arid regions, where natural selection has driven nontrivial physical adaptation toward its separation and collection. For two species of Namib desert beetle whose body geometry makes for a poor filter, subtle modifications in shape and texture have been previously associated with improved performance by facilitating water drainage from its collecting surface. However, little is known about the relevance of these modifications to the flow physics that underlies droplets' impaction in the first place. We find, through coupled experiments and simulations, that such alterations can produce large relative gains in water collection by encouraging droplets to "slip" toward targets at the millimetric scale, and by disrupting boundary and lubrication layer effects at the microscopic scale. Our results offer a lesson in biological fog collection and design principles for controlling particle separation beyond the specific case of fog-basking beetles.

Multi-inspired Janus fabrics with asymmetric coolmax patterns for rapid sweat diffusion and effective sweat-shedding

Janus fabrics with unidirectional liquid transport property have attracted wide attention for their ability to remove excess sweat and lower skin temperature. However, most Janus fabrics face the sweat removal issue on their outer surface when the sweat absorption capacity of their hydrophilic surface reaches limit, which inevitably slows down one-way sweat transport rate and induces the fabrics to become heavy/clingy. Herein, inspired by natural Namib Desert beetles and drip tips, circular Coolmax patterns (severed as sweat extraction points near the skin) and triangular Coolmax patterns (severed as sweat removal zones on the outside of the fabric) are asymmetrically sewn on superhydrophobic cotton fabrics to enable continues one-way sweat transport and allow effective sweat diffusion/shedding on its outer surface. During the sweat transporting and evaporation process, a large amount of heat is dissipated. As a result, the created Janus fabrics can maintain human body temperature about 1.3 ℃ lower than the conventional cotton fabric. Moreover, the low adhesion (∼0.2 mN cm−2) between the wet skin and the fabric makes wearers feel more comfortable. The method can be potentially used for the large-scale commercial production of Janus fabrics and provide insights for the development of smart fabrics in the future.

Bionic Surfaces for Fog Collection: A Comprehensive Review of Natural Organisms and Bioinspired Strategies.

Water scarcity has become a critical global threat, particularly in arid and underdeveloped regions. However, certain insects and plants have evolved the capability to obtain water from fog under these arid conditions. Bionic fog collection, characterized by passive harvesting, minimal energy requirements, and low maintenance costs, has proven to be an efficient method for water harvesting, offering a sustainable water source. This review introduces two superwettable surfaces, namely, superhydrophilic and superhydrophobic surfaces, detailing their preparation methods and applications in fog collection. The fog collection mechanisms of three typical natural organisms, Namib Desert beetles, spider silk, and cactus, along with their bionic surfaces for fog collection devices, are discussed. Additionally, other biological surfaces exhibiting fog transport properties are presented. The main challenges regarding the fabrication and application of bionic fog collection are summarized. Furthermore, we firmly believe that environmentally friendly, low-cost, and stable fog collection materials or devices hold promising prospects for future applications.

Laser-textured biomimetic copper leaf with structural-wettability dual gradient for efficient fog harvesting

Water collection has gradually become research hot topic owing to its potential for alleviating water shortages in arid areas. To date, numerous artificial materials with hierarchical structure have been fabricated to improve water-collecting efficiency. Here, a multi-bioinspired fog-harvesting artificial Cu-Leaf, deriving from Leaf skeletons, Namib desert beetle, and Cactus spines, is fabricated by ultrafast laser selective ablation, chemical etching and chemical vapor deposition, which achieve efficient water-collecting by combining fog capture, droplet growing and directional transportation together. The four-level wedge-shaped tracks of Cu-Leaf skeleton and its wetting property were finely adjusted and their correlations with the fog-harvesting capability were systematically studied. Force analysis related to fog capture, droplet growing and the droplet directional transportation on the hydrophobic/hydrophilic patterned skeleton surfaces have been highlighted. The optimal biomimetic Cu-Leaf performed superior fog-harvesting property with harvesting rate of 544.03 mg/h cm2, which is 2.5 times that of the original Cu sheet. Moreover, we designed an integrated fog-harvesting device (FHD) that could realize the dynamic fog-harvesting and efficient water storage. Therefore, this work enhances the understanding of the fundamental research and provides valuable strategy for design and preparation of sustainable and efficient fog harvesting systems.

Nature-inspired surface for simultaneously harvesting water and triboelectric energy from ambient humidity using polymer brush coatings

Atmospheric water harvesting provides a promising, sustainable solution for alleviating the ever-growing water and energy crisis. Here, inspired by the Namib desert beetle, a wettability patterned surface was designed to simultaneously harvest water and triboelectric energy from ambient moisture. Indium tin oxide (ITO) conductive glass was coated by environmentally friendly perfluoropolyether (PFPE) polymer brushes to obtain a hydrophobic surface, decorated by hydrophilic patterns. The PFPE brushes enabled the droplet to slide down and served as the tribonegative material. The water and triboelectric energy harvesting performance of the hydrophilic-hydrophobic “patterned water and energy harvesting” (P-WEH) system was then investigated. In this regard, a water collection rate of 703 mg cm-2 h-1 was achieved when the P-WEH was placed within an artificial fog. The influence of pattern size and tilt angle, and their relationship with water droplet volume and speed on the triboelectric output, were measured. The effect of the water harvesting area on the output performance of the P-WEH was investigated. The P-WEH with an area of 100 cm2 and a tilt angle of 60° exhibited a high output current of 8.15 µA and a maximum output power of 3.35 µW. Finally, the P-WEH was integrated into a four-season greenhouse to demonstrate its application in reducing external water-energy consumption. This study presents insights into the design of simultaneous water and energy harvesting systems and may contribute to building a sustainable society.

Multi-bioinspired Janus-shedding fabric: One-way sweat transport and rapid sweat removal for improved personal moisture management

In recent years, Janus fabrics that can effectively facilitate personal moisture management have received great attention. However, they are still limited in sweat shedding issue of their superhydrophilic outer surface. Here, inspired by the lotus leaf and Namib Desert beetles, we propose a Janus-shedding fabric with superhydrophilic/hydrophobic patterns and asymmetric wetting property. Through femtosecond-laser microfabrication, we successfully construct superhydrophilic/hydrophobic patterns on the outside surface of Janus fabrics. The method prevents the usage of toxic chemical reagent, thus is completely environmentally-friendly. The as-prepared Janus-shedding fabrics possess one-way liquid transport property. More importantly, the fabrics can achieve rapid liquid/sweat removal on their hydrophilic outer surfaces. The liquid shedding mechanism can be explained that the hydrophilic/hydrophobic patterns on the outer fabric surface can create less surface tension of water which can only fix small volume of water. Moreover, they can maintain human body temperature 3.2 ℃ lower than covered with pristine cotton fabrics. This work provides new insights for the design and fabrication of advanced smart fabrics with both sweat transport and removal property for satisfying the growing demands of personal comfort.

3D-printing-assisted fabrication of hierarchically structured biomimetic surfaces with dual-wettability for water harvesting

Freshwater acquisition methods under various environments are required because water scarcity has intensified worldwide. Furthermore, as water is an essential resource for humans, a freshwater acquisition method that can be utilized even under harsh conditions, such as waterless and polluted water environments, is highly required. In this study, a three-dimensional (3D) printing-assisted hierarchically structured surface with dual-wettability (i.e., surface with both hydrophobic and hydrophilic region) for fog harvesting was developed by mimicking the biological features (i.e., cactus spines and elytra of Namib Desert beetles) that have effective characteristics for fog harvesting. The cactus-shaped surface exhibited self-transportation ability of water droplet, derived from the Laplace pressure gradient. Additionally, microgrooved patterns of the cactus spines were implemented using the staircase effect of 3D printing. Moreover, a partial metal deposition method using wax-based masking was introduced to realize the dual wettability of the elytra of the Namib Desert beetle. Consequently, the proposed surface exhibited the best performance (average weight of 7.85 g for 10 min) for fog harvesting, which was enhanced by the synergetic effect between the Laplace pressure gradient and surface energy gradient. These results support a novel freshwater production system that can be utilized even in harsh conditions, such as waterless and polluted water environments.

On the effects of hybrid surface wettability on the structure of cavitating flow using implicit large eddy simulation

BackgroundSupercavitation flow is characterized by the presence of a supercavity, which can be unstable and cause unwanted motion or even loss of control of an object. To address this issue, flow control techniques are often employed. These techniques aim to manipulate the flow of liquid around the object and improve stability and control. Some of these methods include using control surfaces, injecting fluids, or more advanced techniques such as active flow control or smart materials. MethodThe aim of this study is to use computational methods to investigate the behaviour of supercavitation flow over a Clark-Y hydrofoil with different contact angle patterns (hybrid wettability) inspired by the Namib desert beetle. The hybrid wettability consists of six distinct patterns with a 160-degree contact angle for superhydrophobic surfaces and a five-degree contact angle for superhydrophilic surfaces. To predict the dynamic and unsteady behaviours of the supercavitation flow with a cavity number of 0.4, the implicit large eddy simulation (ILES) technique and Kunz mass transfer model are used. The compressive volume of fluid technique is used in conjunction with dynamic adaptive mesh refinement to track the interface between the vapour and liquid phases. The simulations are conducted using the interPhaseChangeFoam two-phase flow solver within the OpenFOAM framework. This study analyses the time-averaged and instantaneous fluid dynamic properties of the supercavitation flow of the hydrofoil with a hybrid surface, including pressure, velocity, vorticity fields, wake flow, recirculation zone, and liquid volume fraction. In addition, it examines the instantaneous cavity leading edge and flow separation, the vortical flow structure, vorticity stretching and dilatation, spanwise flow details, the creation of a low-pressure zone behind the hybrid hydrofoil, streamwise velocity fluctuations, and the cavity dynamics over an entire cycle. FindingsThe results show that the contact angle has a significant effect on the structure of the supercavitation flow. Specifically, the use of a superhydrophobic surface on the pressure side and trailing edge of a hydrofoil, along with a superhydrophilic surface on the leading edge, can reduce the thickness of the wake zone, the length of the cloud cavity, and flow instability. Additionally, this approach can delay the onset of cavitation.

Radiative cooling layer boosting hydrophilic-hydrophobic patterned surface for efficient water harvesting

Water harvesting from fog is of considerable interest as a nominated solution to freshwater shortage in arid and underdeveloped regions. The unique hydrophilic and hydrophobic patterns on the dorsal surface of the Namib Desert Beetle have been shown to be an evolving and effective strategy for harvesting water from air. Illuminated by the Namib desert beetle, different elaborate patterns based on aluminum plates were established and their water harvesting efficiency was investigated from a comparative perspective. The results showed that the vein-like patterned surfaces had the highest (786.15 mg∙cm−2 h−1) water collection efficiency. However, the heat released during the condensation process affected the water collection rate. In order to reduce the re-evaporation rate of water droplets, a radiant cooling layer was designed on the other side of the water collection plate to release the condensation heat. The radiation cooling layer employed MgHPO4ꞏ0.78 H2O as the functional particle and P(VDF-HFP) as the adhesive. Benefitted from radiative cooling layer, the water collection efficiency could be increased by 198.51 mg∙cm−2 h−1. The water collection material with double-sided function structure has low preparation costs and green raw materials. This work provides an effective way to develop key materials with freshwater harvesting capabilities.

Bioinspired flexible and highly responsive PVDF-based humidity sensors for respiratory monitoring

Humidity sensors have been essential applications in the field of environment protection, agriculture, health care, and so on. It is still focused on preparing sensor materials that can serve as both substrate and humidity sensing layer with low cost, good mechanical flexibility, excellent sensitivity, and reliability. Inspired by the microstructure of the Namib Desert Beetle, in this article, we design a facile method to combine hydrophobic structure with hydrophilic structure and achieve a flexible, responsible, stable sensor (BNFM) based on Zinc oxide NPs-Polyvinylidene fluoride (ZnO-PVDF) with functions of humidity-sensing. Benefiting from the beetle-like microstructure and the specific surface area of the nanofibrous membrane, the BNFM humidity sensor is characterized by an excellent sensitivity of more than 0.7 pF/RH% as well as good response/recovery time (15/7s) within the humidity range from 19 to 92% relative humidity. Besides, the BNFM humidity sensor can be arched inside a mask for real-time detection of human breath conditions. The facile and efficient fabrication technique presents a great platform for the exploration of multifunctional humidity sensors. • Inspired by the microstructure of the Namib desert beetles, designing a facile method to combine hydrophobic structure with hydrophilic structure and preparing a humidity sensor. • The humidity sensor exhibits an excellent sensitivity of more than 0.7 pF/RH% as well as good response/recovery time (15/7s) within the humidity range from 19 to 92% relative humidity. • The sensor can be integrated with a mask and applied to monitor a variety of physiological signals, which effectively verifies the excellent sensing performance of the humidity sensor. • Showing the sensing mechanism for the Beetle-like structured humidity sensor to explain the highly sensitive properties of the fabricated sensor.

Flexible bioinspired PDMS-paper based surface with hybrid wettability for droplet collection and detection

The superwettable surface inspired by Namib Desert beetle and lichen have provided outstanding ability in controlling droplets and great potential for the development of functional surfaces. However, the expensive, time-consuming and complex fabrication process limits extensive application. In this work, a superwettable surface including polydimethylsiloxane (PDMS)-based superhydrophobic (SPO) area and paper-based superhydrophilic (SPI) sites is prepared by laser-etched without special chemical modification, which is simply, pattern controllable and environmentally friendly. On SPO area, the water contact angle (WCA) is 151.3° and water sliding angle (WSA) is 4°, but the WCA of SPI site is almost 0°. Therefore, droplets are repelled by SPO area and tightly locked in SPI sites without spilling. The surface with excellent stability and flexibility is extended to portable testing materials for droplet collection, arrays and colorimetric detection. The PDMS-paper based surface is proved feasibility in application of colorimetry, such as pH, nitrite, starch and protein. This work provides inspiration for simply manufacturing of flexible superwettable patterned surfaces and shows potential applications in sample collection and portable testing, which is of significance to the design of portable testing materials, development of small devices and application of intelligent detection.

Heterostructured MoS2 quantum dot/GO lamellar membrane with improved transport efficiency for organic solvents inspired by the Namib Desert beetle

Graphene oxide lamellar 2D membranes are widely researched for ion separation and molecular sieving in aqueous solution. Extension of the research of GO-based membranes for organic solvent nanofiltration has drawn much attention but is still in its infancy. The relatively low solvent permeability remains a difficult problem to overcome. Inspired by the shell of the Namib Desert beetle, a heterostructured lamellar membrane was prepared by incorporating MoS 2 quantum dots (MQDs) into the graphene oxide membrane. A dual-functional zone was formed, where hydrophilic areas exhibited excellent absorption performance for polar solvents and hydrophobic regions were propitious to the discharge of polar solvents when incorporating a moderate amount (10%) MQDs, denoted as GM-10 (nonpolar solvents presented the opposite performance). The synergistic effects of the dual-functional zone successfully improved the transport efficiency for various solvents, and the flux of various solvents for GM-10 was over three times higher than that of the pure GO membrane. Simultaneously, the composite biomimetic membrane showed excellent stability. This paper provides a novel strategy for constructing a heterostructured dual-functional zone for 2D lamellar membrane modification without the sacrifice of rejection, revealing the potential for further optimization of separation performance and membrane stability. • The biomimetic membrane was prepared by adding MoS 2 quantum dots into graphene oxide membrane. • Heterostructured dual-functional zone was formed, enhancing the transport efficiency. • The membrane showed excellent balanced separation performance for various dye organic solvents. • The membrane showed high stability in harsh condition and long-term operation.

Rapid and efficient oil removal from O/W emulsions by hydrophobic porous polystyrene microspheres embedded with hydrophilic surface micro-regions

Inspired by Namib Desert beetle’s back which is patterned with different wetting properties, hydrophobic porous polystyrene microspheres embedded with hydrophilic surface micro-regions (HPHs) were designed and fabricated by the radical copolymerization in the W1/O/W2 double Pickering emulsions with high internal water phase. The synergistic effect of the hydrophobic surface and the hydrophilic surface micro-regions results in HPHs exhibiting superior performances for separating both surfactant-free and surfactant-stabilized O/W emulsions. After 60 s hand-shaking, the oil was absorbed and stored within HPHs which could be separated from the water using a 600-mesh sieve, and the TOC values of purified water could be reduced to 2.06 ± 0.06–67.38 ± 2.02 ppm when the initial oil content was 1 vol%. Meanwhile, HPHs could be recovered and reused through a simple treatment. The excellent oil removal efficiency was kept even after 50 cycles. High oil removal efficiency, general applicability, easy operation and excellent recyclability endow HPHs with great potential for practical applications. And this work provides a facile and general way to prepare porous polymer microspheres with wettability contrast surfaces.

Design of a Venation-like Patterned Surface with Hybrid Wettability for Highly Efficient Fog Harvesting.

Inspired by Namib Desert beetle and leaf venation, a wettability-integrated system consisting of wettability-hybrid coatings and venation-like patterns was designed and successfully fabricated via a simple, low-cost, and eco-friendly route. The as-prepared surface can construct a 3D topography with a water layer and efficiently drain through the venation-like patterns. The combination of multiple mechanisms enhances the fog harvesting ability significantly. Meanwhile, the synergistic mechanisms of fog harvesting enhancement by a wettability-integrated surface were further studied and discussed.