Dual-Functional Superhydrophobic Textiles with Asymmetric Roll-Down/Pinned States for Water Droplet Transportation and Oil-Water Separation

Adaptive Surfaces with Stimuli-Responsive Wettability: From Tailoring to Applications

Adaptive surfaces with tunable wettability have attracted considerable attention due to their increasing importance in adapting to real applications. By incorporation of stimuli-sensitive materials that enable control over surface chemistry or topographical features, or both, a variety of adaptive surfaces are engineered to exhibit reversible tailoring in wettability. This Review provides a comprehensive review of the development of adaptive surfaces with stimuli-responsive wettability. It begins by outlining the background and significance of the adaptive surfaces. Then, this Review delves into the fundamental theories that govern surface wettability, focusing on the influence of external stimuli on wetting behavior. The discussion then shifts to highlighting various triggers, such as magnetism, photo, temperature, pH, electricity, and gas stimuli, that drive response in wettability, as well as surfaces that respond to dual or multiple stimuli. This Review further explores the primary and leading applications in droplet manipulation, oil-water separation, and water harvesting. To conclude, we encapsulate the challenges, potential solutions, and future directions for improving tunable wettability on these surfaces.

Fluorine-Free Multi-durable Superhydrophobic Cotton Fabrics Prepared by an Atomization Spraying Method for Self-Cleaning and Oil-Water Separation

Superhydrophobic textiles have special applications in many fields such as medical treatment, military protection, oil-water separation, etc. In the large-scale pad-dry-cure process, a large number of polymer binders are often added to improve the superhydrophobic durability, resulting in a significant reduction in air permeability. To address this issue, a low-liquid atomization spray method was adopted to fabricate multi-durable superhydrophobic cotton fabrics using N1,N6-bis(2,3-epoxypropyl)hexane-1,6-diamine, a silica precursor, and fluorine-free hexadecyltrimethoxysilane as the main modifiers. The prepared fabric maintained excellent water repellency even after being subjected various harsh conditions tests such as 2000 cycles of friction, 40 washing cycles, ultrasonic treatment for 120 min, 200 tape peelings, and acid-alkali-salt corrosion for 24 h. The air permeability of the superhydrophobic fabric was measured to be 370.2 L m-2 s-1, which was merely 5% lower than that of the original fabric, indicating that the modified fabric retains satisfactory air permeability. The modified fabric exhibited an excellent self-cleaning effect with respect to various liquids. In addition, the prepared fabric showed good oil-water separation capability for both heavy and light oils. For heavy oil-water mixtures, the fabric sample exhibited a maintenance of 98.13% separation efficiency and a high flux of 18 032 L m-2 h-1 after 10 uses. These findings will help to promote the practical application of low-feed interface modification technology in the production of durable functional textiles.

High-Durability Photothermal Slippery Surfaces for Droplet Manipulation Based on Ultraviolet Lithography

Photothermal slippery surface has broad applications in many research fields for noncontacting, loss-free, and flexible droplet manipulation capability. In this work, with specific morphologic parameters and modified base materials doped by Fe₃O₄, a high-durability photothermal slippery surface (HD-PTSS) was proposed and implemented based on ultraviolet (UV) lithography to achieve repeatability of more than 600 cycles. The instantaneous response time and transport speed of HD-PTSS were related to near-infrared ray (NIR) powers and droplet volume. Meanwhile, the durability was closely related to the morphology of HD-PTSS, which impacts the recovering of a lubricant layer. The droplet manipulation mechanism of HD-PTSS was discussed in depth, and the Marangoni effect was found to be the key factor for the durability of HD-PTSS.

Removal of dyes, oils, alcohols, heavy metals and microplastics from water with superhydrophobic materials

A wide variety of pollutants can be currently found in water that are extremely difficult to remove due to their chemical composition and properties. A lot of effort has been made to tackle this issue that directly affects the environment. In this scenario, superhydrophobic surfaces, which have a water contact angle >150°, have emerged as an innovative technology that could be applied in different ways. Their environmental applications show promise in removing emerging pollutants from water. While the number of publications on superhydrophobic materials has remained largely unchanged since 2019, the number of articles on the environmental applications of superhydrophobic surfaces is still rising, corroborating the interest in this area. Herein, we briefly present the basis of superhydrophobicity and show the different materials that have been used to remove pollutants from water. We have identified five types of emerging pollutants that are efficiently removed by superhydrophobic materials: oils, microplastics, dyes, heavy metals, and ethanol. Finally, the future challenges of these applications are also discussed, considering the state of the art of the environmental applications of superhydrophobic materials.

3D-Printed Parahydrophobic Functional Textile with a Hierarchical Nanomicroscale Structure

Functional textiles with superhydrophobicity and high adhesion to water, called parahydrophobic, are attracting increasing attention from industry and academia. The hierarchical (micronanoscale) surface patterns in nature provide an excellent reference for the manufacture of parahydrophobic functional textiles. However, the replication of the complex parahydrophobic micronanostructures in nature exceeds the ability of traditional manufacturing strategies, which makes it difficult to accurately manufacture controllable nanostructures on yarn and textiles. Herein, a two-photon femtosecond laser direct writing strategy with nanoscale process capability was utilized to accurately construct the functional parahydrophobic yarn with a diameter of 900 μm. Inspired by rose petals, the parahydrophobic yarn is composed of a hollow round tube, regularly arranged micropapillae (the diameter is 109 μm), and nanofolds (the distance is 800 nm) on papillae. The bionic yarn exhibited a superior parahydrophobic behavior, where the liquid droplet not only was firmly adhered to the bionic yarn at an inverted angle (180°) but also presented as spherical on the yarn (the maximum water contact angle is 159°). The fabric woven by the bionic yarn also exhibited liquid droplet-catching ability even when tilted vertically or turned upside down. Based on the excellent parahydrophobic function of bionic yarn, we demonstrated a glove that has very wide application potential in the fields of water droplet-based transportation, manipulation, microreactors, microextractors, etc.

A versatile "3M" methodology to obtain superhydrophobic PDMS-based materials for antifouling applications

Fouling, including inorganic, organic, bio-, and composite fouling seriously affects our daily life. To reduce these effects, antifouling strategies including fouling resistance, release, and degrading, have been proposed. Superhydrophobicity, the most widely used characteristic for antifouling that relies on surface wettability, can provide surfaces with antifouling abilities owing to its fouling resistance and/or release effects. PDMS shows valuable and wide applications in many fields, and due to the inherent hydrophobicity, superhydrophobicity can be achieved simply by roughening the surface of pure PDMS or its composites. In this review, we propose a versatile "3M" methodology (materials, methods, and morphologies) to guide the fabrication of superhydrophobic PDMS-based materials for antifouling applications. Regarding materials, pure PDMS, PDMS with nanoparticles, and PDMS with other materials were introduced. The available methods are discussed based on the different materials. Materials based on PDMS with nanoparticles (zero-, one-, two-, and three-dimensional nanoparticles) are discussed systematically as typical examples with different morphologies. Carefully selected materials, methods, and morphologies were reviewed in this paper, which is expected to be a helpful reference for future research on superhydrophobic PDMS-based materials for antifouling applications.

Smart Hierarchical Zeolitic Imidazolate Framework-Coated Stainless Steel Meshes with Switchable Wettability for Oil/Water Separation

Selective filtration based on superwetting materials has brought about widespread attention in the field of oil/water separation. In this study, a ZIF-L@8-coated stainless steel mesh (ZIF-L@8-coated SSM) was prepared via in situ growth of two-dimensional leaf-shaped ZIF-L nanosheets on SSM, followed by heterogeneous epitaxial growth of ZIF-8 on a ZIF-L coating. The synthesized ZIF-L@8-coated SSM with a hierarchical micro/nanoscale structure exhibited outstanding switchable wettability between underwater superoleophobicity and underoil superhydrophobicity upon respective prewetting using water and oil without additional external stimuli. It possessed excellent separation performances and stabilities with respect to various types of oil/water mixtures. The switchable wettability mechanism was analyzed and elucidated in detail. The synthesized ZIF-L@8-coated SSM with switchable wettability in this study would have great potential in on-demand oil/water separation.

Facile Fabrication of Superhydrophobic Graphene/Polystyrene Foams for Efficient and Continuous Separation of Immiscible and Emulsified Oil/Water Mixtures

Three-dimensional superhydrophobic/superlipophilic porous materials have attracted widespread attention for use in the separation of oil/water mixtures. However, a simple strategy to prepare superhydrophobic porous materials capable of efficient and continuous separation of immiscible and emulsified oil/water mixtures has not yet been realized. Herein, a superhydrophobic graphene/polystyrene composite material with a micro-nanopore structure was prepared by a single-step reaction through high internal phase emulsion polymerization. Graphene was introduced into the polystyrene-based porous materials to not only enhance the flexibility of the matrix, but also increase the overall hydrophobicity of the composite materials. The resulting as-prepared monoliths had excellent mechanical properties, were superhydrophobic/superoleophilic (water/oil contact angles were 151° and 0°, respectively), and could be used to continuously separate immiscible oil/water mixtures with a separation efficiency that exceeded 99.6%. Due to the size-dependent filtration and the tortuous and lengthy micro-nano permeation paths, our foams were also able to separate surfactant-stabilized water-in-oil microemulsions. This work demonstrates a facile strategy for preparing superhydrophobic foams for the efficient and continuous separation of immiscible and emulsified oil/water mixtures, and the resulting materials have highly promising application potentials in large-scale oily wastewater treatment.

Design of Robust Self-Healing Silicone Elastomers Based on Multiple H-Bonding and Dynamic Covalent Bond

A room-temperature self-healing silicone elastomer was prepared based on the synergistic effect of multiple H-bonding and dynamic covalent bond. The multiple bonds constructed by inserting thiourea into the polyurea network can inhibit the crystallization of hard urea H-bonds segments and activate the diffusion movement of polymer chains. Dynamic imine endows materials with a strong connection for the fracture interface by imine metathesis. The effect of thiourea on urea H-bonds was confirmed by the Fourier transform infrared spectrum, which showed obvious changes of H-bond density according to peak revolution of C═O and N-H. Differential scanning calorimetry demonstrated the transition from the crystalline to amorphous state after the introduction of thiourea. Tensile tests and scratch-healing tests showed that this design method can improve the self-healing property without sacrificing the mechanical strength. Finally, the optimized self-healing process was analyzed from the perspectives of the contact process, the interpenetration diffusion of the polymer chain, and rebuilding of crosslinking points between the two interfaces, which would build an avenue for constructing a fast, self-healing, and tough material.

Preparation of multifunctional long-persistent photoluminescence cellulose fibres

Simple preparation of flame-retardant, photoluminescent, and superhydrophobic smart nanocomposite coating was developed and applied onto cotton fibres using the simple pad-dry-cure technique. This novel strategy involved the immobilization of rare-earth-doped aluminium strontium oxide (ASO; SrAl₂ O₄ :Eu⁺² ,Dy⁺³ ) nanoparticles, environmentally friendly room temperature vulcanizing silicone rubber (RTV) and environmentally friendly Exolet AP422 (Ex). The fabrics were also able to produce a char film in the fire-resistant assessment, providing fibres with a self-extinguishing characteristic. Furthermore, the fire-retardant performance of the coated cotton samples remained resistant to washing over 35 laundry cycles. The superhydrophobicity of the treated fabrics was monitored to improve by increasing the photoluminescent phosphor nanoparticles. The produced transparent photoluminescent film displayed an absorption at 360 nm and an emission at 526 nm. The photoluminescent fabrics were observed to generate different colorimetric shades, including white, green-yellow and bright white as monitored by Commission Internationale de l'Éclairage laboratory colorimetric coordinates. Slow emissions were detected for the treated cotton fabrics as monitored by emission, ultraviolet-visible light absorption, lifetime, and decay time spectral profiles to indicate glow in the dark phosphorescence effect. Both comfort and mechanical properties of the coated fibres were evaluated by measuring their bending length and air permeability.

Smart Bionic Surfaces with Switchable Wettability and Applications

In order to satisfy the needs of different applications and more complex intelligent devices, smart control of surface wettability will be necessary and desirable, which gradually become a hot spot and focus in the field of interface wetting. Herein, we review interfacial wetting states related to switchable wettability on superwettable materials, including several classical wetting models and liquid adhesive behaviors based on the surface of natural creatures with special wettability. This review mainly focuses on the recent developments of the smart surfaces with switchable wettability and the corresponding regulatory mechanisms under external stimuli, which is mainly governed by the transformation of surface chemical composition and geometrical structures. Among that, various external stimuli such as physical stimulation (temperature, light, electric, magnetic, mechanical stress), chemical stimulation (pH, ion, solvent) and dual or multi-triggered stimulation have been sought out to realize the regulation of surface wettability. Moreover, we also summarize the applications of smart surfaces in different fields, such as oil/water separation, programmable transportation, anti-biofouling, detection and delivery, smart soft robotic etc. Furthermore, current limitations and future perspective in the development of smart wetting surfaces are also given. This review aims to offer deep insights into the recent developments and responsive mechanisms in smart biomimetic surfaces with switchable wettability under external various stimuli, so as to provide a guidance for the design of smart surfaces and expand the scope of both fundamental research and practical applications.

Smart Control for Water Droplets on Temperature and Force Dual-Responsive Slippery Surfaces

Responsive slippery lubricant-infused porous surfaces (SLIPSs), featuring excellent liquid repelling/sliding capabilities in response to external stimuli, have attracted great attention in smart droplet manipulations. However, most of the reported responsive SLIPSs function under a single stimulus. Here, we report a kind of smart slippery surface capable of on-demand control between sliding and pinning for water droplets via alternately freezing/thawing the stretchable polydimethylsiloxane sheet in different strains. Diverse parameters are quantified to investigate the critical sliding volume of the droplet, including lubricant infusion amount, laser-scanning power, and pillar spacing. By virtue of the cooperation of temperature and force fields acting on the SLIPS, we demonstrate the intriguing applications including controllable chemical reaction and on-demand electrical circuit control. We envision that this dual-responsive surface should provide more possibilities in smart control of microscale droplets, especially in active vaccine-involved biochemical microreactions where a lower temperature is highly favored.

Photo-switchable smart superhydrophobic surface with controllable superwettability

An azobenzene-based smart superhydrophobic surface undergoes reversible transformations among multiple bioinspired superwetting states through photo-manipulation, demonstrating promising potential on a rewritable platform for droplet transportation.

Preparation of Fluorine-Free Superhydrophobic Paper with Dual-Response of Temperature and pH

Although various superhydrophobic materials have been manufactured and effectively used for oil–water separation, it is still highly desirable to explore materials which are eco-friendly, low-cost, and multifunctional. In this paper, a stable copolymer solution was prepared from the fluorine-free superhydrophobic copolymer with dual-responsiveness of temperature and pH. The functional superhydrophobic paper was prepared by immersing paper in copolymer solution by the dip-coating method. The surface element and structure analysis of the prepared superhydrophobic paper shows that the dual-responsive copolymer adheres successfully to the surface of the paper without destroying the fiber structure of the paper. At pH ≥ 7 and T > 25 °C, the paper has a good superhydrophobic performance, while under the conditions of pH < 7 and T < 25 °C, the paper comes into a hydrophilic state. Therefore, the dual-responsive superhydrophobic paper is more likely to adapt to the complicated oil-water separation environment than the single-response.

Switchable Isotropic/Anisotropic Wettability and Programmable Droplet Transportation on a Shape-Memory Honeycomb

Programmable droplet transportation is required urgently but is still challenging. In this work, breath figure was employed to fabricate shape-memory poly(lactic acid) (PLLA) honeycombs in which tiny crystals and an amorphous network act as the shape-fixed phase and recovery phase, respectively. Upon uniaxial tension, circle pores from the breath figure were deformed to elliptical pores, producing contact angle differences and anisotropic wetting behaviors in two directions. Both pore geometry and anisotropic wettability can be tailored via the draw ratio. On the PLLA honeycomb surface with a lower draw ratio, the contact angle difference is too small to induce droplet transportation along the desired direction. In the case of a higher draw ratio, however, the movement of water droplets has been controlled absolutely along the tension direction. The transition between them can be achieved reversibly during uniaxial tension and recovery processes based on the shape-memory effect. The enhanced flow control, which can be attributed to the synergism between optimal hydrophobicity and enlarged anisotropic wetting behaviors, endows water droplets with the ability to turn a corner spontaneously on a V-shaped surface including two regions exhibiting different oriented directions.

A4 Paper Chemistry: Synthesis of a Versatile and Chemically Modifiable Cellulose Membrane

Multifunctional cellulose membranes were developed from A4-sized printing paper via chemical modification. A4 paper is a widely used and easily accessible product with high cellulose content. Inspired by cellulose chemistry, we report a simple modification of the A4 paper, converting it from a common office supply to a user-modifiable functionalized cellulose membrane for practical applications. The hydroxyl groups of cellulose enable a facile tuning of its internal structure and polarity via chemical modification. In addition, the functionalized cellulose membrane has more stable mechanical strength compared to commercial cellulose-based filtration membranes. As a proof-of-concept, we demonstrate the separation of a water/oil mixture using the functionalized A4 membrane; we have extended this idea to origami-assisted membrane applications. Finally, this versatile A4 paper chemistry may offer a promising strategy for the development of functional membranes.

In Situ Reversible Tuning from Pinned to Roll-Down Superhydrophobic States on a Thermal-Responsive Shape Memory Polymer by a Silver Nanowire Film

Shape memory polymer (SMP) surfaces with tunable wettability have attracted extensive attention due to their widespread applications. However, there have been rare reports on in situ tuning wettability with SMP materials. In this paper, we reported a kind of distinct superhydrophobic SMP microconed surface on the silver nanowire (AgNW) film to achieve in situ reversible transition between pinned and roll-down states. The mechanism is taking advantage of the in situ heating functionality of the silver nanowire film by voltage, which provides the transition energy for SMP to achieve the fixation and recovery of temporary shape. It is noteworthy that the reversible transition could be repeated many times (>100 cycles), and we quantitatively investigate the shape memory ability of microcones with varied height and space under different applied voltages. These results show that the tilted microcones could recover its original upright state under a small voltage (4-11 V) in a short time, and the shortest recovery time is about 0.5 min under an applied voltage of ∼10 V. Finally, we utilize SMP microcone arrays with tunable wettability to realize lossless droplet transportation, and the tilted microconed surface also achieves liquid unidirectional transport due to its anisotropic water adhesion force. The robust microconed SMP surface with reversible morphology transitions will have far-ranging applications including droplet manipulation, reprogrammable fog harvesting, and so on.

The fabrication of mechanically durable and stretchable superhydrophobic PDMS/SiO2 composite film

Stretchable superhydrophobic film was fabricated by casting silicone rubber polydimethylsiloxane (PDMS) on a SiO₂ nanoparticle-decorated template and subsequent stripping. PDMS endowed the resulting surface with excellent flexibility and stretchability. The use of nanoparticles contributed to the sustained roughening of the surface, even under large strain, offering mechanically durable superhydrophobicity. The resulting composite film could maintain its superhydrophobicity (water contact angle ≈ 161° and sliding angle close to 0°) under a large stretching strain of up to 100% and could withstand 500 stretching–releasing cycles without losing its superhydrophobic properties. Furthermore, the obtained film was resistant to long term exposure to different pH solutions and ultraviolet light irradiation, as well as to manual destruction, sandpaper abrasion, and weight pressing.

Stretchable superhydrophobic film was fabricated by casting silicone rubber polydimethylsiloxane (PDMS) on a SiO₂ nanoparticle-decorated template and subsequent stripping.

Photothermal Actuation of Diverse Liquids on an Fe3O4-Doped Slippery Surface for Electric Switching and Cell Culture

The photoinduced manipulation of liquids on a slippery lubricant-infused porous surface (SLIPS) has attracted a tremendous amount of attention because of its merits of contactless stimulation and excellent spatial and temporal control. However, tedious fabrication methods by a combination of template transfer and fluorination for a photothermal-material-doped SLIPS and the lack of deeper systematically quantitative analysis with respect to droplet hydrokinetics are greatly perplexing in both academic research and industrial applications. Here we demonstrate a kind of Fe₃O₄-doped SLIPS by one-step femtosecond laser cross-scanning, which can readily steer diverse liquids toward arbitrary directions with a fast velocity of up to 1.15 mm/s in the presence of a unilateral NIR stimulus. The underlying mechanism is that the wettability gradient force (F_wet-grad) induced by the temperature gradient arising from asymmetric near-infrared-irradiation (NIR) loading would be generated within 1 s to actuate a targeted droplet's sliding behavior. Through tuning the NIR irradiating sites, we can slide a targeted droplet with controllable directions and routes. On the basis of fundamental physics, we have quantitatively analyzed the relationship among Fe₃O₄-doped content, lubricant rheological performance, droplet wettability variations, F_wet-grad, and the sliding velocity for diverse liquid species. Accordingly, we can remotely steer liquid droplets to realize the on-off state of an electrical circuit on demand, the droplet fusion of a microfluidic reactor, and the culture/inhibition of biological cells.

Multifunctional Magnetocontrollable Superwettable-Microcilia Surface for Directional Droplet Manipulation

In nature, fluid manipulations are ubiquitous in organisms, and they are crucial for many of their vital activities. Therefore, this process has also attracted widescale research attention. However, despite significant advances in fluid transportation research over the past few decades, it is still hugely challenging to achieve efficient and nondestructive droplet transportation owing to contamination effects and controllability problems in liquid transportation applications. To this end, inspired by the motile microcilia of micro-organisms, the superhydrophobicity of lotus leaves, the underwater superoleophobicity of filefish skin, and pigeons' migration behavior, a novel manipulation strategy is developed for droplets motion. Specifically, herein, a superwettable magnetic microcilia array surface with a structure that is switchable by an external magnetic field is constructed for droplet manipulation. It is found that under external magnetic fields, the superhydrophobic magnetic microcilia array surface can continuously and directionally manipulate the water droplets in air and that the underwater superoleophobic magnetic microcilia array surface can control the oil droplets underwater. This work demonstrates that the nondestructive droplet transportation mechanism can be used for liquid transportation, droplet reactions, and micropipeline transmission, thus opening up an avenue for practical applications of droplet manipulation using intelligent microstructure surfaces.

Durable and Scalable Candle Soot Icephobic Coating with Nucleation and Fracture Mechanism

Ice formation and accretion affect residential and commercial activities. Icephobic coatings decrease the ice adhesion strength (τ_ice) to less than 100 kPa. However, rare icephobic coatings remove the ice under the action of gravity or natural winds. The icephobicity of such coatings depends on materials with low interfacial toughness. We develop durable candle soot icephobic coating with RTV-1 as a low-modulus binding material. Heterogeneous nucleation on 20-40 nm candle soot particles and their fracture mechanism are discussed. The developed coating always shows durable Cassie-Baxter superhydrophobic state with low ice adhesion (18 kPa) and maintains the τ_ice value of about 25 kPa after severe mechanical abrasion, 30 liquid nitrogen/water cycles, 100 frosting/defrosting cycles, 100 icing/deicing cycles, acid/base exposure, under UV light, and exposure to natural freezing rain in Hangzhou. In addition, the proposed technique is time-efficient, inexpensive, and suitable for large-scale applications.

Multifunctional Superwettable Material with Smart pH Responsiveness for Efficient and Controllable Oil/Water Separation and Emulsified Wastewater Purification

Developing multifunctional superwettable materials is highly demanded in the oil/water separation field but remains challenging due to the critical limitations of complex fabrication strategy and high cost. Herein, based on the cost-effective kaolin nanoparticles, we present a convenient and mild strategy for fabricating a smart superwettable material with multiple excellent performances, such as pH-responsive water wettability, self-cleaning property, favorable buoyancy, and air purification performance. By virtue of the dual rough surface structure and special chemical composition, the resultant material surface exhibits a superior pH-dependent wettability, which can be reversibly switched between superamphiphobicity and superhydrophilicity-superoleophobicity for many times in accordance with the pH value of the corresponding aqueous solution. As a result, the obtained superwettable material with reversible and controllable water wettability can be applied in efficient and continuous separation of multiple types of oil/water mixtures, especially the highly emulsified oil/water emulsions, via in situ or ex situ wettability change. To our knowledge, the smart material with the wetting property of superamphiphobicity that can be used for continuous emulsified wastewater purification has been rarely discussed in the emerging research works. In addition, the as-prepared material presents universal applicability to diversiform substrates and exhibits robust durability and stability against high-concentration salt solutions and rigorous mechanical abrasion. All of these above-mentioned advantages indicate that the as-prepared superwettable material will hold great potential in various practical applications, including oily wastewater remediation, smart aquatic device fabrication, liquid droplet manipulation, guiding liquid movement, and optimizing multiple operations in industrial fields.

Under-liquid dual superlyophobic nanofibrous polymer membranes achieved by coating thin-film composites: a design principle

Surfaces with under-liquid dual superlyophobicity have garnered tremendous interest because of their promising applications, but their unexplored underlying nature restricts the designed construction of such surfaces. Herein, we coated the thin-film composites with different terminal groups over the electrospun polyacrylonitrile nanofibrous membranes, which afforded the membranes excellent stability in organic solvents, as well as modulated under-liquid wetting behaviors. Among them, the representative under-liquid dual superlyophobic 4-cyan-Ph-terminated membrane could realize highly efficient separation of all types of oil/water mixtures and even emulsions. Moreover, we found that the under-liquid wetting behaviors could be classified in terms of the intrinsic water contact angle (θ w). By comparing the total interfacial energy, we proved that the under-liquid dual lyophobic surfaces were thermodynamically metastable. On this basis, we could predict the θ w of rough surfaces with the under-liquid dual lyophobicity in a given oil-water-solid system (e.g., 47.3-89.1° in cyclohexane-water-solid system, R = 2). This work provides a design principle for the fabrication of under-liquid dual superlyophobic surfaces, which will open potential applications in diverse fields in terms of such smart surfaces.

Gecko toe pads inspired in situ switchable superhydrophobic shape memory adhesive film

Recently, smart adhesive superhydrophobic surfaces have attracted much attention. However, it is still a challenge to obtain a superhydrophobic surface with shape memory adhesive performance. Herein, inspired by the special back-scrolling/unfolding ability of gecko toe pads and corresponding tunable adhesion, we report such a film produced by sticking a layer of superhydrophobic pillar structured polyurethane (s-PU) onto a shape memory polyurethane-cellulose nanofiber (PU-CNF) substrate to mimic the hair-like skin structure and underlying muscle of the gecko toe pads, respectively. Similar to the muscle of the gecko toe pads, the excellent shape memory effect of the PU-CNF substrate can help the obtained film to memorize and repeatedly display different shapes and solid/water contact models. Thus reversible switching between multiple states from the low-adhesive rolling performance to the high-adhesive pinning performance can be realized. Meanwhile, based on its smart wetting performance, not only the traditional in situ capture/release of one microdroplet, but also the step-by-step release of different droplets can be realized on our film. This work reports a new superhydrophobic shape memory adhesive film, which offers a novel strategy for surface adhesion control and meanwhile opens a new road for applications in controlled droplet manipulation.

Robust Superhydrophobic Cotton Fibers Prepared by Simple Dip-Coating Approach Using Chemical and Plasma-Etching Pretreatments

The preparation of superhydrophobic textiles with high mechanical and chemical durability is challenging. Here, facile and fluorine-free methods, using alkali and plasma-etching treatments, followed by the addition of silica nanoparticles and tetraethyl orthosilicate (TEOS), were used to prepare superhydrophobic cotton surfaces. With different input variables and etching techniques, superhydrophobic cotton fabrics with high chemical and mechanical durability were successfully prepared, with contact angles up to 173°. A control of the surface architecture at the nanoscale in combination with a homogeneous repellent layer of TEOS in the cotton surface was achieved. The repellent properties of the as-prepared cotton remain stable under accelerated laundering and abrasion test conditions. The etching pretreatment by alkali or plasma plays a key role in obtaining superhydrophobic cotton surfaces.

Recent advances of bioinspired functional materials with specific wettability: from nature and beyond nature

Through 3.7 billion years of evolution and natural selection, plants and animals in nature have ingeniously fulfilled a broad range of fascinating functions to achieve optimized performance in responding and adapting to changes in the process of interacting with complex natural environments. It is clear that the hierarchically organized micro/nanostructures of the surfaces of living organisms decisively manage fascinating and amazing functions, regardless of the chemical components of their building blocks. This conclusion now allows us to elucidate the underlying mechanisms whereby these hierarchical structures have a great impact on the properties of the bulk material. In this review, we mainly focus on advances over the last three years in bioinspired multiscale functional materials with specific wettability. Starting from selected naturally occurring surfaces, manmade bioinspired surfaces with specific wettability are introduced, with an emphasis on the cooperation between structural characteristics and macroscopic properties, including lotus leaf-inspired superhydrophobic surfaces, fish scale-inspired superhydrophilic/underwater superoleophobic surfaces, springtail-inspired superoleophobic surfaces, and Nepenthes (pitcher plant)-inspired slippery liquid-infused porous surfaces (SLIPSs), as well as other multifunctional surfaces that combine specific wettability with mechanical properties, optical properties and the unidirectional transport of liquid droplets. Afterwards, various top-down and bottom-up fabrication techniques are presented, as well as emerging cutting-edge applications. Finally, our personal perspectives and conclusions with regard to the transfer of micro- and nanostructures to engineered materials are provided.

Biomimetic fabrication of superhydrophobic loofah sponge: robust for highly efficient oil-water separation in harsh environments

Oil/water separation has become an increasingly important field due to frequent industrial oily wastewater emission and crude oil spill accidents. Herein, we fabricate a robust superhydrophobic loofah sponge via a versatile, environmentally friendly, and low-cost dip coating strategy, which involves the modification of commercial loofah sponge with waterborne polyurea and fused SiO2 nanoparticles without the modification of any toxic low-surface-energy compound. The as-prepared loofah sponge showed excellent superhydrophobic/superoleophilic properties and exhibited robustness for effective oil-water separation in extremely harsh environments (such as 1 M HCl, 1 M NaOH, saturated NaCl solution and hot water higher than 95 °C) due to the remarkably high chemical stability. In addition, the as-prepared loofah sponge was capable of excellent anti-fouling, has self-cleaning ability and could act as the absorber for effective separation of surfactant-free oil-in-water emulsions. More importantly, the as-prepared loofah sponge demonstrated remarkable robustness against strong sandpaper abrasion and finger wipes, while retaining its superhydrophobicity and efficient oil/water separation efficiency even after more than 50 abrasion cycles. This facile and green synthesis approach presented here has the advantage of large-scale fabrication of a multifunctional biomass-based adsorbent material as a promising candidate in anti-fouling, self-cleaning, and versatile water-oil separation.