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a,b) The optical top and side view of slant lotus leaf. There is a similar elliptical shape on the lotus surface along the slant direction. The ellipse with smaller curvature radius at the peak region and larger curvature radius at the bottom of the lotus leaf is observed and shown as the black dotted curves. The mature leaf edge warps symmetrically on both side of the longer axis of its ellipse, but asymmetrically on both side of the short axes of ellipse, which induce gravity shift variance on the surface. With the long‐term operation, the leaf slants and even bends the petiole. c) The mature lotus leaf always slightly slants for removing the water or contaminant on the surface. d) The magnified optical view of the lotus surface. The surface is covered by submillimeter papillae (SP) and micro papillae. e,f) The SEM images of the lotus leaf surface. e) The SP are characterized by height of ≈100–120 µm, root diameter of ≈100‐120 µm, and streamlined chamfer at the root region, which distribute outside of the elliptical shape. From the external edge of ellipse to the leaf edge, the distribution density increases and the space between two neighbor papillae decreases from around 1000 µm to 400 µm. f) The micro papillae with average diameter of 10–12 µm distribute uniformly on the leaf surface.
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Automatic slant of lotus leaf achieving self‐motive unidirectional fluid transport is significant for self‐cleaning, decreasing load, enhancing respiration, and receiving more sunlight, which is the consequence of natural evolution. In this study, the mechanism of the automatic gradual slant process in its development is exposed and this function i...
Citations
... For example, the surface of nano-materials can be easily destroyed when a large strain occurs, and in fact, nano-materials are always destroyed by the application of dynamic force. 22,23 To enhance the duration of surfaces based on micro-/nano-topography, some protection strategies were proposed in previous studies. For example, Li et al. proposed using a multi-level structure design to improve the overall structural mechanical properties, 24 while Wang et al. suggested using an excellent structural design to avoid contact with nanomaterials from an external force. ...
Optimal design of flexible micro-topography is of fundamental importance for numerous applications, such as in membranes, sensors, and MEMS. Different from rigid micro-topography, surfaces displaying flexible micro-topography are able to absorb external energy by transforming their shape, which makes them suitable to be used under complex operating conditions. In this study, we find that the micro-structures occurring on biological natural surfaces all have a common structural feature, namely, an ellipsoid shape. The flexible sleek micro-structures without right angles are able to decrease the stress concentration and deformation in the loading process, which may prevent the nano-structures from being damaged on the upper surfaces. To clearly understand the performance of these micro-topographies, a series model is established by force analysis. The model uncovers the design principles that lead to the mechanical enhancement of natural composites for expanding the application of flexible micro-/nano-structured membranes.
... Increasing the temperature to the glass transition temperature of a flexible polymer can activate molecular chain mobility and alter the elasticity of the polymer [54][55][56][57][58]. Employing such a flexible polymer with shape memory can achieve the reversible control of surface microstructure, which further controls the adhesion [54,59,60]. ...
Diverse unique surfaces exist in nature, e.g. lotus leaf, rose petal and rice leaf. They show similar contact angles but different adhesion properties. According to the different wettability and adhesion characteristics, this review reclassifies different contact states of droplets on surfaces. Inspired by the biological surfaces, smart artificial surfaces have been developed which respond to external stimuli and consequently switch between different states. Responsive surfaces driven by various stimuli, e.g. stretching, magnetic, photo, electric, temperature, humidity and pH, are discussed. Studies reporting on either atmospheric or underwater environments are discussed. The application of tailoring surface wettability and adhesion includes microfluidics/droplet manipulation, liquid transport and harvesting, water energy harvesting and flexible smart devices. Particular attention is placed on the horizontal comparison of smart surfaces with the same stimuli. Finally, the current challenges and future prospects in this field are also identified.
... 5,15 In addition, solid dust may be easily captured by a water droplet, and once it is wetted, it cannot get out of the water droplet due to the large surface tension and excellent wettability of water. [16][17][18][19][20] Fig. S1 and Movie Online Resource 2 † show a captured solid particle that oats in the water droplet. In this process, water lters the air. ...
Stomata, specialized functional openings distributed on the leaf surface, are used for plant respiration by allowing gas exchange, i.e., taking in carbon dioxide and releasing oxygen, and for water content regulation. Their function is vital to plant survival. Leaves with different wettability exhibit different stomata densities. In this study, we find that stomata on Pistia stratiotes L. leaves are protected by superhydrophobic setae, which prevent direct contact between the stomata and water in humid environments by suspending water droplets on the top of the setae. Thus, oxygen and carbon dioxide are freely exchanged through the stomata. This structure inspired us to design and develop a mask for filtering solid particles and noxious gas from the atmosphere. The incoming gas is in convective contact with water, achieving a filtering efficiency. The solid particles and potential harmful gas in air are wetted and captured by water, leaving fresh air for healthy breathing. This novel design has potential applications in the treatment of respiratory diseases.
Biomimetic synthesis provides potential guidance for the synthesis of bio‐nanomaterials by mimicking the structure, properties and functions of natural materials. Behavioral studies of biological surfaces with specific micro/nano structures are performed to explore the interactions of various molecules or organisms with biological surfaces. These explorations provide valuable inspiration for the development of biomimetic surfaces with similar effects. This work reviews some conventional preparation methods and functional modulation strategies for biomimetic interfaces. It aims to elucidate the important role of biomimetic interfaces with antifouling and low‐pollution properties that can replace non‐environmentally friendly coatings. Thus, biomimetic antifouling interfaces can be better applied in the field of marine antifouling and antimicrobial. In this review, the commonly used fabrication methods for biomimetic interfaces as well as some practical strategies for functional modulation is present in detail. These methods and strategies modify the physical structure and chemical properties of the biomimetic interfaces, thus improving the wettability, adsorption, drag reduction, etc. that they exhibit. In addition, practical applications are presented of various biomimetic interfaces for antifouling and look ahead to potential biomedical applications. By continuously discovering functional surfaces with biomimetic properties and studying their microstructure and macroscopic properties, more biomimetic interfaces will be developed.
Fast and stable water drainage is essential for living organisms, drainage plane construction, and protection of infrastructure from damage during rainfall. Unlike traditional anti-overflow drainage methods that rely on hydrophobic or sharped edges, this study demonstrates a bottom overflow-induced drainage model inspired by the water path employed by Pontederia crassipes leaves, leading to fast and stable drainage. A superhydrophilic bottom surface guides water to overflow and pin at the bottom of a thin sheet, resulting in dripping at a higher frequency and reduced water retention. This bottom drainage idea assists large-scale thin sheets to function as efficient and stable drainage surfaces in simulated rain environments. The flexible thin sheet can also be feasibly attached to dusty substrates to effectively remove dusty rainwater with slight dust residue. The bioinspired approach presented herein suggests a promising potential for efficient water drainage on outdoor functional photovoltaic surfaces, such as solar panels and radomes, thus ensuring effective energy conversion and stable signal transmission.
Metal materials are susceptible to the influence of environmental media, and chemical or electrochemical multiphase reactions occur on the metal surface, resulting in the corrosion of metal materials which can...
The robust self-cleaning of a lotus leaf is the most classic and powerful phenomenon in nature, whose hybrid papillae and biological wax guarantee its functions. The stability of the lotus leaf surface function is determined by its overall structural design, and is also the fundamental reason for its long-term survival in the natural environment. In fact, the durability of lotus leaf surface function is facilitated by the coordination of many factors which is why it is challenging to be investigated using bionic technology. In this review, we comprehensively examined the synergistic effects of flexible characteristics, surface topography, hollow interlayers, leaf shape, and bent petioles on the structural stability of the lotus leaf surface. The key significance of these factors is in transferring the stress and strain on the surface downwards, reducing the load on the surface, improving the durability of the self-cleaning function, and ultimately ensuring respiration and photosynthesis of leaves in the natural environment. This comprehensive scrutiny offers a novel classical bionic scheme for enhancing the structural stability of a surface, which has potential for applications in deepwater self-cleaning, anti-drag, anti-icing, thermal insulation, and mechanical enhancement of membranes and buildings.
High wetting resistance membranes are developed to reduce wetting issues during membrane distillation (MD). Functionalization agents are used to improve the wetting characteristics of the prepared membranes. In this study, two pristine membranes of polyvinylidene fluoride with different solvents (N-methyl-2-pyrrolidone and triethyl phosphate) were prepared to compare their wetting characteristics. The polyvinylidene fluoride/triethyl phosphate (PTEP) membrane exhibited a high liquid entry pressure (LEP) of 2.63 bar, while the polyvinylidene fluoride/N-methyl-2-pyrrolidone membrane obtained a lower LEP of 0.30 bar. In this work, an ideal natural water repellent was introduced to synthesize a high wetting resistance membrane with comparison of fluoroalkyl silane. The selected PTEP membrane was improved by adding functionalized montmorillonite (Mt) with 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane (FOTS, fs-Mt) and carnauba wax (fw-Mt). The addition of fs-Mt and fw-Mt particles to the PTEP membrane significantly increased the LEP and contact angle (CA) of the prepared membranes. The Pfw-Mt membrane obtained the highest LEP value (4.10 bar) with a CA of 124°. The permeate flux of Pfs-Mt and Pfw-Mt membranes improved to 6.86 and 4.12 L/m2h, respectively, after 16 h of separation. Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy proved the absence of Na and Cl elements in the inner morphology of Pfw-Mt membranes after 24 h of direct contact membrane distillation. Hence, Pfw-Mt membrane can be an alternative MD membrane for salt removal in long-term operation due to the self-cleaning effect that prevents membrane fouling.
