Infused-liquid-switchable porous nanofibrous membranes for multiphase liquid separation

Alcohol-gating femtosecond laser-induced micro/nano-structured membranes with reversible switching wettability and breathability

A reversible liquid gating membrane with the ability to regulate gas/liquid transport is critical for many fields, such as biological applications, multiphase separation, and sewerage treatment. Numerous membranes can respond to external stimuli and dynamically control gas/liquid fluid transport; however, simultaneously achieving regulated gas/liquid transport membranes through simple manufacturing remains a challenge. In this work, we investigated an alcohol-regulation gating membrane via femtosecond laser one-step processing, allowing in situ dynamically controllable gas/liquid transfer. More specifically, the porous membrane, processed by laser, exhibits excellent superhydrophobicity (WCA ∼ 153.4°) and breathability (water-vapor evaporation rates ∼118.3 mg (cm2 h)-1), enabling gas to penetrate but not water. In contrast, it allows the passage of water while preventing the permeation of gas subsequent to the introduction of alcohol. Furthermore, the porous membrane still possesses superbly consistent performance after being placed in air for 90 days or over 100 dropping-drying ethanol cycles test, indicating outstanding durability and reversibility. Significantly, the porous membrane has broad potential applications in medical dressings, providing a new strategy to fabricate next-generation bandages.

Fluid Unidirectional Transport Induced by Structure and Ambient Elements across Porous Materials: From Principles to Applications

Spontaneous or nonspontaneous unidirectional fluid transport across multidimension can occur under specific structural designs and ambient elements for porous materials. While existing reviews have extensively summarized unidirectional fluid transport on surfaces, there is an absence of literature summarizing fluid's unidirectional transport across porous materials. This review introduces wetting phenomena observed on natural biological surfaces or porous structures. Subsequently, it offers an overview of diverse principles and potential applications in this field, emphasizing various physical and chemical structural designs (surface energy, capillary size, topographic curvature) and ambient elements (underwater, under oil, pressure, and solar energy). Applications encompass moisture-wicking fabric, sensors, skincare, fog collection, oil-water separation, electrochemistry, liquid-based gating, and solar evaporators. Additionally, significant principles and formulas from various studies are compelled to offer readers valuable references. Simultaneously, potential advantages and challenges are critically assessed in these applications and the perspectives are presented.

Noncontact Microfluidics of Highly Viscous Liquids for Accurate Self-Splitting and Pipetting

Accurate dosing for various liquids, especially for highly viscous liquids, is fundamental in wide-ranging from molecular crosslinking to material processing. Despite droppers or pipettes being widely used as pipetting devices, they are powerless for quantificationally splitting and dosing highly viscous liquids (>100 mPa s) like polymer liquids due to the intertwined macromolecular chains and strong cohesion energy. Here, a highly transparent photopyroelectric slippery (PS) platform is provided to achieve noncontact self-splitting for liquids with viscosity as high as 15 000 mPa s, just with the assistance of sunlight and a cooling source to provide a local temperature difference (ΔT). Moreover, to guarantee the accuracy for pipetting liquids (>80%), the ultrathin MXene film (within a thickness of 20 nm) is self-assembled as the photo-thermal layers, overcoming the trade-off between transparency and photothermal property. Compared with traditional pipetting strategies (≈1.3% accuracy for pipetting polymer liquids), this accurate microfluidic chip shows great potential in adhesive systems (bonding strength, twice than using the droppers or pipettes).

Amphiphilic Superspreading Polymer Membranes Prepared by Capillary Force-Driven Self-Assembly

To overcome the two main obstacles of large-scale application of superspreading material, self assembly is used to prepare superspreading polymer membrane (SPPM) in this work. An amphiphilic SPPM is prepared by capillary force-driven self assembly using PP melt-blown nonwovens and polyvinyl alcohol (PVA). The prepared SPPM has low preparation cost and stable performance since self assembly needs low energy consumption, and the production is thermodynamically stable. By using cryo-electron microscopy, transmission electron microscopy, X-ray photoelectron spectrum and scanning electron microscope with energy dispersive X-ray spectroscopy. It is proved that PVA is successfully assembled on the fiber surface of PP melt-blown nonwovens. The prepared SPPM has excellent spreading performance, the "spreading times" of both water and oil are less than 0.5 s. They showed much superior performance compared to traditional materials when applied in oil-water separation, seawater desalination, and ion separation. This work will definitely promote the development of self assembly, superspreading materials, and related sciences.

Hybrid-Electrolytes System Established by Dual Super-lyophobic Membrane Enabling High-Voltage Aqueous Lithium Metal Batteries

Aqueous electrolytes and related aqueous rechargeable batteries own unique advantage on safety and environmental friendliness, but coupling high energy density Li-metal batteries with aqueous electrolyte still represent challenging and not yet reported. Here, this work makes a breakthrough in "high-voltage aqueous Li-metal batteries" (HVALMBs) by adopting a brilliant hybrid-electrolytes strategy. Concentrated ternary-salts ether-based electrolyte (CTE) acts as the anolyte to ensure the stability and reversibility of Li-metal plating/stripping. Eco-friendly water-in-salt (WiS) electrolyte acts as catholyte to support the healthy operation of high-voltage cathodes. Most importantly, the aqueous catholyte and non-aqueous anolyte are isolated in each independent chamber without any crosstalk. Aqueous catholyte permeation toward Li anode can be completely prohibited without proton-induced corrosion, which is enabled by the introduction of under-liquid dual super-lyophobic membrane-based separator, which can realize the segregation of the most effective immiscible electrolytes with a surface tension difference as small as 6 mJ m-2. As a result, the aqueous electrolyte can be successfully coupled with Li-metal anode and achieve the fabrication of HVALMBs (hybrid-electrolytes system), which presents long-term cycle stability with a capacity retention of 81.0% after 300 cycles (LiNi0.8Mn0.1Co0.1O2 || Li (limited) cell) and high energy density (682 Wh kg-1).

Spontaneous thermal energy transfer and anti-gravitational water pumping using Al2O3 fiber-enhanced flexible nonwoven material as a high-performance and self-floating solar evaporator

Solar-driven evaporation is promising to address water scarcity. However, preserving the heat inside evaporators instead of allowing run-off, and synergistically utilizing it to wick water from the bulk, is still underexplored. Herein, a dual-functional bridge of longitudinal orientated channels of Al2O3 fibers (AOFs) embedded in a multi-layered nonwoven evaporator was proposed to create a buffer for spontaneous thermal conduction and anti-gravitational water pumping. As a self-floating system with high porosity and flexibility, benefiting from the strong water transporting ability and high thermal conductivity of the AOFs, a superhigh evaporation rate (2.79 kg m-2 h-1 under 1 sun) can be achieved with great stability and durability. This work highlights the potential of promoting thermal management using a large-scale vapour chamber and mass-producible nonwoven technology to prepare a high-performance evaporator for practical applications.

Spontaneous Separation of Immiscible Organic Droplets on Asymmetric Wedge Channels with Hierarchical Microchannels

Spontaneous separation of immiscible organic droplets has substantial research implications for environmental protection and resource regeneration. Compared to the widely explored separation of oil-water mixtures, there are fewer reports on separating mixed organic droplets on open surfaces due to the low surface tension differences. Efficient separation of mixed organic liquids by exploiting the rapid spontaneous transport of droplets on open surfaces remains a challenge. Here, through the fusion of inspiration from the fast droplet transport capability of Sarracenia trichome and the asymmetric wedge channel structure of shorebird beaks, this work proposes a spine with hierarchical microchannels and wedge channels (SHMW). Due to the synergistic effect of capillary force and asymmetric Laplace force, the SHMW can rapidly separate mixed organic droplets into two pure phases without requiring additional energy. In particular, the self-spreading of the oil solution on the open channel surface is utilized to amplify the surface energy difference between two droplets, and SHMW achieves the pickup of oil droplets floating on the surface of the organic solution. The maximum separation efficiency on 3-SHMW can reach 99.63%, and it can also realize the antigravity separation of mixed organic droplets with a surface tension difference as low as 0.87 mN·m-1. Furthermore, SHMW performs controllable separation, oil droplet pickup, and continuous separation and collection of mixed organic droplets. It is expected that this cooperative structure composed of hierarchical microchannels and wedge channels will be realized in resource recovery or chemical reactions in industrial production processes.

Rechargeable Multifunctional Anti-Bacterial AEMs for Electrodialysis: Improving Anti-Biological Performance via Synergistic Antibacterial Mechanism

Constructing a functional layer on the surface of commercial membrane (as a substrate) to inhibit the formation of biofilms is an efficient strategy to prepare an antibacterial anion exchange membrane (AEM). Herein, a rechargeable multifunctional anti-biological system is reported by utilizing the mussel-inspired L-dopa connection function on commercial AEMs. Cobalt nanoparticles (Co NPs) and N-chloramine compounds are deposited on the AEM surface by a two-step modification procedure. The anti-biofouling abilities of the membranes are qualitatively and quantitatively analyzed by adopting common Gram-negative (E. coli) and Gram-positive (S. aureus & Bacillus) bacteria as model biofouling organisms. The optimized membrane exhibits a high stability concerning the NaCl solution separation performance within 240 min. Meantime, the mechanism of the anti-adhesion is un-veiled at an atomic level and molecular dynamics (MD) simulation are conducted to measure the interaction, adsorption energy and average loading by using lipopolysaccharide (LPS) of E. coli. In view of the superior performance of antibacterial surfaces, it is believed that this work could provide a valuable guideline for the design of membrane materials with resistance to biological contamination.

Three-Dimensional Imaging of Emulsion Separation through Liquid-Infused Membranes Using Confocal Laser Scanning Microscopy

The removal of emulsified oils from water has always been a challenge due to the kinetic stability resulting from the small droplet size and the presence of stabilizing agents. Membrane technology can treat such mixtures, but fouling of the membrane leads to dramatic reductions in the process capacity. Liquid-infused membranes (LIMs) can potentially resolve the issue of fouling. However, their low permeate flux compared with conventional hydrophilic membranes remains a limitation. To gain insight into the mechanism of transport, we use 3D images acquired by confocal laser scanning microscopy (CLSM) to reconstruct the sequence of events occurring during startup and operation of the LIM for removal of dispersed oil from oil-in-water emulsions. We find evidence for coalescence of oil droplets on the surface of and formation of oil channels within the LIM. Using image analysis, we find that the rate at which oil channels are formed within the membrane and the number of channels ultimately govern the permeate flux of oil through the LIMs. Oil concentration in the feed affects the rate of coalescence of oil on the surface of the LIM, which, in turn, affects the channel formation dynamics. The channel formation dynamics also depend on the viscosity of the infused liquid and the operating pressure. A higher affinity to the pore wall for infused liquid than permeating liquid is essential to antifouling behavior. Overall, this work offers insight into the selective permeation of a dispersed liquid phase through a LIM.

Dual-bionic superwetting gears with liquid directional steering for oil-water separation

Developing an effective and sustainable method for separating and purifying oily wastewater is a significant challenge. Conventional separation membrane and sponge systems are limited in their long-term usage due to weak antifouling abilities and poor processing capacity for systems with multiple oils. In this study, we present a dual-bionic superwetting gears overflow system with liquid steering abilities, which enables the separation of oil-in-water emulsions into pure phases. This is achieved through the synergistic effect of surface superwettability and complementary topological structures. By applying the surface energy matching principle, water and oil in the mixture rapidly and continuously spread on preferential gear surfaces, forming distinct liquid films that repel each other. The topological structures of the gears facilitate the overflow and rapid transfer of the liquid films, resulting in a high separation flux with the assistance of rotational motion. Importantly, this separation model mitigates the decrease in separation flux caused by fouling and maintains a consistently high separation efficiency for multiple oils with varying densities and surface tensions.

Structured electroplating sludge derived membrane for one-step removal of oil, metal ions, and anions from oil/water emulsions

The effective simultaneous treatment of hazardous waste sludge and complex oil/water emulsions in one way is urgently desired but still a challenging issue. Herein, this work for the first time presents a green and efficient strategy to fabricate an electroplating sludge (ES) derived multifunctional self-supporting membrane for the one-step removal of emulsified oils, soluble metal ions, and anions in complex oily wastewater. Due to low cost of ES and sustainability of the solvent selected in fabrication process, the large-scale application of the membrane is easily to promote. The assembled hierarchical nanostructure endowed robust underwater superoleophobicity of the membrane even under various corrosive aqueous environments, as well as excellent ultra-low oil adhesion and anti-oil-fouling performance, without chemical modification. Significantly, the multifunctional membrane possessed desirable simultaneous separation efficiency for five typical oil-in-water emulsions (>99.4%, high oil/water selective wettability), including crude oil-in-water emulsion with high viscosity (>99.6%), Cu²⁺ (>96.1%, surface complexation and ionic exchange), and Cl^- (>92.7%, electrostatic attraction). Therefore, this green, low-cost, and multifunctional membrane not only allows the large-scale resource utilization of hazardous waste sludge, but also effectively solves the problems of complex oily wastewater purification.

Non-Stop Switching Separation of Superfine Solid/Liquid Dispersed Phases in Oil and Water Systems Using Polymer-Assisted Framework Fiber Membranes

Fabricating filtration membranes with wide applicability and high efficiency is always a challenge in the precise separation of small colloidal particles under mild conditions. For this purpose, a strategy mixing supramolecular framework fiber with polymer is adopted. The fibrous assembly in the gel state provides uniform nanopores for both channel and interception and controlled wettability for lyophilic/lyophobic switching. The used polymer fills the gaps between fiber assemblies and improves the mechanical property. The composite membrane shows both under-oil superhydrophobic and underwater superoleophobic nature, which allows the conversions via in situ modulation of joystick solvents. Based on surface wetting and size-sieving, ultrafine hard nanoparticles dispersing in both hydrophobic organic solvents and water are selectively sieved. In addition, on-demand separation of water-in-oil and oil-in-water microemulsions without and with surfactants as systems containing soft droplets are realized. The smallest cut-off size of ≈3 nm is achieved for both hard and soft emulsions, while separation efficiency maintains during sustained in situ reversible switches.

Droplet impacting dynamics: Recent progress and future aspects

Droplet impact behaviours are widely applied in a variety of domains including self-cleaning, painting and coating, corrosion of turbine blades and aircraft, separation and oil repellency, anti-icing, heat transfer and droplet electricity generation, etc. The wetting behaviours and impact dynamics of droplets on solid and liquid surfaces involve complex solid-liquid and liquid-liquid interfacial interactions. The modulation of droplet dynamics by means of specific surface morphology and hydrophobic/hydrophilic patterns, which in turn can be derived to related applications, is one of the current promising interests in the interfacial effect modulating droplet dynamics. This review provides a detailed overview of several scientific aspects of droplet impact behaviours and heat transfer processes influenced by multiple factors. Firstly, the essential wetting theory and the fundamental parameters of impinging droplets are introduced. Secondly, the effects of different parameters on the dynamic behaviours and heat transfer of impinging droplet are discussed. Finally, the potential applications are listed. Existing concerns and challenges are summarized and future perspectives are provided to address poorly understood and conflicting issues.

Mussel-Inspired Robust Peony-like Cu3(PO4)2 Composite Switchable Superhydrophobic Surfaces for Bidirectional Efficient Oil/Water Separation

To alleviate the economic and environmental damage caused by industrial discharges of oily wastewater, materials applied for efficient oil/water separation are receiving significant attention from researchers and engineers. Among others, switchable wettable materials for bidirectional oil/water separation show great potential for practical applications. Inspired by mussels, we utilized a simple immersion method to construct a polydopamine (PDA) coating on a peony-like copper phosphate surface. Then, TiO₂ was deposited on the PDA coating surface to build a micro-nano hierarchical structure, which was modified with octadecanethiol (ODT) to obtain a switchable wettable peony-like superhydrophobic surface. The water contact angle of the obtained superhydrophobic surface reached 153.5°, and the separation efficiency was as high as 99.84% with a flux greater than 15,100 L/(m²·h) after 10 separation cycles for a variety of heavy oil/water mixtures. Notably, the modified membranes have a unique photoresponsiveness, transforming to superhydrophilic upon ultraviolet irradiation, achieving separation efficiencies of up to 99.83% and separation fluxes greater than 32,200 L/(m²·h) after 10 separation cycles for a variety of light oil/water mixtures. More importantly, this switch behavior is reversible, and the high hydrophobicity can be restored after heating to achieve efficient separation of heavy oil/water mixtures. In addition, the prepared membranes can maintain high hydrophobicity under acid-base conditions and after 30 sandpaper abrasion cycles, and damaged membranes can be restored to superhydrophobicity after a brief modification in the ODT solution. This simple-to-prepare, easy-to-repair, robust membrane with switchable wettability shows great potential in the field of oil/water separation.

Overflow Control for Sustainable Development by Superwetting Surface with Biomimetic Structure

Liquid flowing around a solid edge, i.e., overflow, is a commonly observed flow behavior. Recent research into surface wetting properties and microstructure-controlled overflow behavior has attracted much attention. Achieving controllable macroscale liquid dynamics by manipulating the micro-nanoscale liquid overflow has stimulated diverse scientific interest and fostered widespread use in practical applications. In this review, we outline the evolution of overflow and present a critical survey of the mechanism of surface wetting properties and microstructure-controlled liquid overflow in multilength scales ranging from centimeter to micro and even nanoscale. We summarize the latest progress in utilizing the mechanisms to manipulate liquid overflow and achieve macroscale liquid dynamics and in emerging applications to manipulate overflow for sustainable development in various fields, along with challenges and perspectives.

Special Superwetting Materials from Bioinspired to Intelligent Surface for On-Demand Oil/Water Separation: A Comprehensive Review

Since superwetting surfaces have emerged, on-demand oil/water separation materials serve as a new direction for meeting practical needs. This new separation mode uses a single porous material to allow oil-removing and water-removing to be achieved alternately. In this review, the fundamentals of wettability are systematically summarized in oil/water separation. Most importantly, the two states, bioinspired surface and intelligent surface, are summarized for on-demand oil/water separation. Specifically, bioinspired surfaces include micro/nanostructures, bioinspired chemistry, Janus-featured surfaces, and dual-superlyophobic surfaces that these superwetting materials can possess asymmetric wettability in one structure system or opposite underliquid wettability by prewetting. Furthermore, an intelligent surface can be adopted by various triggers such as pH, thermal and photo stimuli, etc., to control wettability for switchable oil/water separation reversibly, expressing a thought beyond nature to realize innovative oil/water separation by external stimuli. Remarkably, this review also discusses the advantages of all the materials mentioned above, expanding the separation scope from the on-demand oil/water mixtures to the multiphase immiscible liquid-liquid mixtures. Finally, the prospects of on-demand oil/water separation materials are also concluded.

Superwetting membrane-based strategy for high-flux enrichment of ethanol from ethanol/water mixture

Ethanol, which can be scalable produced from fermented plant materials, is a promising candidate to gasoline as the next-generation liquid fuel. As an energy-efficient alternative to distillation, membrane-based strategies including pervaporation and reverse osmosis have been developed to recover ethanol from fermentation broths. However, these approaches suffer the drawback of low separation flux. Herein, we report a superwetting membrane system to enrich ethanol from water in a high-flux manner. By synergistically regulating surface energy of the solid porous membrane and hydration between an additive inorganic potassium salt and water, concentrated ethanol can rapidly wetting and permeate the porous membrane, with the salt solution being blocked. Using this newly developed superwetting membrane system, we can achieve fast enrichment of ethanol from water, with flux of two orders magnitude higher than that of pervaporation and reverse osmosis membranes.

Topographical Design and Thermal-Induced Organization of Interfacial Water Structure to Regulate the Wetting State of Surfaces

Smart surfaces with superhydrophobic/superhydrophilic characteristics can be controlled by external stimuli, such as temperature. These transitions are attributed to the molecular-level conformation of the grafted polymer chains due to the varied interactions at the interface. Here, tunable surfaces were prepared by grafting two well-known thermo-responsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(oligoethylene glycol)methyl ether acrylate (POEGMA₁₈₈) onto micro-pollen particles of uniform morphology and roughness. Direct Raman spectra and thermodynamic analyses revealed that above the lower critical solution temperature, the bonded and free water at the interface partially transformed to intermediate water that disrupted the "water cage" surrounding the hydrophobic groups. The increased amounts of intermediate water produced hydrogen bonding networks that were less ordered around the polymer grafted microparticles, inducing a weaker binding interaction at the interface and a lower tendency to wet the surface. Combining the roughness factor, the bulk surface assembled by distinct polymer-grafted-pollen microparticles (PNIPAM or POEGMA₁₈₈) could undergo a different wettability transition for liquid under air, water, and oil. This work identifies new perspectives on the interfacial water structure variation at a multiple length scale, which contributed to the temperature-dependent surface wettability transition. It offers inspiration for the application of thermo-responsive surface to liquid-gated multiphase separation, water purification and harvesting, biomedical devices, and printing.

Light-responsive nanochannels based on the supramolecular host–guest system

The light-responsive nanochannel of rhodopsin gained wider research interest from its crucial roles in light-induced biological functions, such as visual signal transduction and energy conversion, though its poor stability and susceptibility to inactivation in vitro have limited its exploration. However, the fabrication of artificial nanochannels with the properties of physical stability, controllable structure, and easy functional modification becomes a biomimetic system to study the stimulus-responsive gating properties. Typically, light-responsive molecules of azobenzene (Azo), retinal, and spiropyran were introduced into nanochannels as photo-switches, which can change the inner surface wettability of nanochannels under the influence of light; this ultimately results in the photoresponsive nature of biomimetic nanochannels. Furthermore, the fine-tuning of their stimulus-responsive properties can be achieved through the introduction of host–guest systems generally combined with a non-covalent bond, and the assembling process is reversible. These host–guest systems have been introduced into the nanochannels to form different functions. Based on the host–guest system of light-responsive reversible interaction, it can not only change the internal surface properties of the nanochannel and control the recognition and transmission behaviors but also realize the controlled release of a specific host or guest molecules in the nanochannel. At present, macrocyclic host molecules have been introduced into nanochannels including pillararenes, cyclodextrin (CD), and metal–organic frameworks (MOFs). They are introduced into the nanochannel through chemical modification or host–guest assemble methods. Based on the changes in the light-responsive structure of azobenzene, spiropyran, retinal, and others with macrocycle host molecules, the surface charge and hydrophilic and hydrophobic properties of the nanochannel were changed to regulate the ionic and molecular transport. In this study, the development of photoresponsive host and guest-assembled nanochannel systems from design to application is reviewed, and the research prospects and problems of this photo-responsive nanochannel membrane are presented.

Wetting-Induced Water Promoted Flow on Tunable Liquid-Liquid Interface-Based Nanopore Membrane System

Membrane separation provides effective methods for solving the global water crisis. Contemporary membrane systems depend on interfacial interactions between liquid and solid membrane matrixes. However, it may lead to a limiting permeate flux due to the large flow resistance at hydrophobic liquid-solid interfaces. Herein, the liquid-liquid interface with improved interface energy is reversibly introduced in membrane systems to boost wetting and reduce transport resistance. A series of interfaces were systematically explored to reveal mechanisms of wetting and boosted flow performances, which are further supported by simulations. Findings of this study highlight that interfacial liquids with lower surface energies, lower viscosities, and higher solubilities can effectively improve water flow without sacrificing rejection performance, achieving by transforming a solid-liquid interface into liquid-liquid interface interaction. It provides a concept to design advanced membrane systems for water purification (e.g., desalination and oil-water separation) and energy conversion processes.

Bioinspired Superspreading Surface: From Essential Mechanism to Application

ConspectusThe dynamic behavior of liquids on surfaces is ubiquitous in nature and has aroused wide attention from researchers. Among them, the superspreading surface has been extensively investigated and applied in areas ranging from film fabrication to antibiofouling, separation, etc. However, the traditional equilibrium contact angle (CA) at the thermodynamic steady-state cannot completely depict the dynamic spreading process of liquids, because the performance of these surfaces is controlled not only by the final steady superhydrophilicity (CA < 5°) but also by the superspreading speed of liquids with a CA of ∼0°. Moreover, as the most basic prerequisite for superspreading, the long-held intrinsic wetting threshold (IWT) of 90°, which divides hydrophobic and hydrophilic surfaces, is also controversial.In this Account, we summarize and condense the commonalities of our related research, further formally propose the concept of "superspreading", and recommend using "superspreading time (ST)" and "curve of superspreading radius versus spreading time (SRST)" to quantify its performance. Learning from nature is the most effective way to artificially fabricate superspreading surfaces. To begin, we first review some typical superspreading surfaces we found in nature and introduce the strategies adopted by the surfaces for surviving or realizing special functions. Then, we systematically review our recent understanding of the essential mechanism of superspreading surfaces across multiple length scales─from the molecular origin of the newly found IWT of ∼65° for water to the macroscopic respective functions of nanostructure and microstructure in superspreading. Armed with the in-depth fundamental mechanism, we propose the designing principle of high-performance superspreading surfaces. Following that, we summarize the commonly utilized methods, including modifying surface composition to give the surface intrinsic hydrophilicity and changing surface structure to improve the superspreading performance. Subsequently, we introduce the recently developed practical applications by virtue of the outstanding property of the superspreading surface, including the fabrication of a self-assembled film on the solid-gas surface and solid-liquid interface, a self-assembled water barrier for antibiofouling and oil repellency, high-efficiency separation and heat dissipation, etc. Finally, we discuss the remaining major challenges and the future development trends in the superspreading field. This Account serves to arouse wide attention and efforts in the superspreading field to strengthen mechanism research and promote practical large-area applications.

Ag/polydopamine-coated textile for enhanced liquid/liquid mixtures separation and dye removal

Engineering a versatile platform that enables to separate both oil/water and oil/oil mixtures and remove dye from water is not easy. To address this challenge, we have developed an Ag/polydopamine-coated textile (Ag/PDA@textile) by chemically depositing Ag particles on the textile surface using polydopamine as the binder layer. The obtained Ag/PDA@textile attracts water but repels oil in the air, underwater, and when immersed into the oil. Exploiting its water-attracting and oil resistance, the Ag/PDA@textile is acted as a separation membrane to separate oil/water mixtures with enhanced separation efficiency. The Ag/PDA@textile also possesses opposite wetting behavior to oils with different polarities, allowing it to separate oil/oil mixtures efficiently. Thanks to the catalytic performance of the Ag particle, organic dyes can be decomposed effectively by our Ag/PDA@textile under UV illustration or in the presence of NaBH₄. Our Ag/PDA@textile may be valuable for applications in water purification and oil sewage treatment.

Slippery, Water-Infused Membrane with Grooved Nanotrichomes for Lubricating-Induced Oil Repellency

Water, abundant and ubiquitous in nature, is an easy yet powerful resource for the creatures to survive by putting together with their topologies interfacing their living environment. Here, a slippery, water-infusing surface (SWIS) that retains a thick and stable water layer on the membrane is presented, robustly maintaining the oil repellency against the pressure and friction of immiscible liquids. Inspired by the plant trichome structures and their function, grooved nanotrichome, formed on the fibrous membrane by the oxygen plasma etching, induces robust water lubrication on the SWIS. SWIS membrane repels and separates highly viscous and adhesive oils in air and underwater by preventing oils from adhering to the lubricating surface. Repeated tests both in air and underwater confirm the antiadhesion and self-cleaning properties of the SWIS. The SWIS oil scooper, fixed on a frame with a handle, successfully collects spilled oil on a pilot-scale oil spill site and a real ocean oil spill site by simply scooping and recovering the oil. In addition, SWIS membrane is expected to help protect environments with further applications such as oil-wastewater treatment and oil separation in food.

Light-Controlled Ionic/Molecular Transport through Solid-State Nanopores and Nanochannels

Biological nanochannels perfectly operate in organisms and exquisitely control mass transmembrane transport for complex life process. Inspired by biological nanochannels, plenty of intelligent artificial solid-state nanopores and nanochannels are constructed based on various materials and methods with the development of nanotechnology. Specially, the light-controlled nanopores/nanochannels have attracted much attention due to the unique advantages in terms of that ion and molecular transport can be regulated remotely, spatially and temporally. According to the structure and function of biological ion channels, light-controlled solid-state nanopores/nanochannels can be divided into light-regulated ion channels with ion gating and ion rectification functions, and light-driven ion pumps with active ion transport property. In this review, we present a systematic overview of light-controlled ion channels and ion pumps according to the photo-responsive components in the system. Then, the related applications of solid-state nanopores/nanochannels for molecular sensing, water purification and energy conversion are discussed. Finally, a brief conclusion and short outlook are offered for future development of the nanopore/nanochannel field.

Superamphiphilic Chitosan Cryogels for Continuous Flow Separation of Oil-In-Water Emulsions

Chitosan is a typical hydrophilic biomass building block widely used in material science and engineering. However, its intrinsic amphiphilicity has been seldom noted so far. Herein, a series of glutaraldehyde-crosslinked chitosan cryogels with superamphiphilicity are fabricated at moderately frozen conditions through a freezing-thawing process. The micron-sized porous cryogel samples display a 0° contact angle toward both water and oil, 0° water contact angle under oil, and over 120° oil contact angle underwater. By comparing the wetting behavior of the tablet compressed by pure chitosan powders, the superamphiphilicity of the chitosan sample is proven to be independent on crosslinkers. This special wettability endows the chitosan cryogels with high separation efficiency for various surfactant-stabilized oil-in-water emulsions under continuous flow mode driven by gravity as well as a peristaltic pump.

Electrospun Liquid-Infused Membranes for Emulsified Oil/Water Separation

From an environmental perspective, microfiltration membranes are attractive for the separation of emulsified oils from contaminated water. However, fouling of the membrane is a major drawback of the technology. "Liquid-infused membranes" (LIMs) have the potential to eliminate membrane fouling. Here, we demonstrate the practical application of LIMs for the separation of oil from a stable oil-in-water emulsion and characterize their resistance to fouling. The base membrane is an electrospun nonwoven fibrous layer of the fluorinated copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP). The surface energy of the PVDF-co-HFP fibers was lowered by the covalent attachment of a fluorinated silane (PFOCTS), and then, the membrane was infused with a perfluoropolyether. The membrane was then challenged with model emulsions of dodecane in water in a cross-flow configuration. This PFOCTS-modified LIM showed better infused liquid stability, permeation selectivity, higher permeate flux than the unmodified LIM, and better anti-fouling properties than the bare membrane without infused liquid. We also examine the mechanism for transport of the dispersed oil phase through the liquid-infused membrane. We find a linear relationship between the dodecane flux and dodecane concentration in the feed and a higher dodecane flux through the PFOCTS-modified membrane than the unmodified one, which suggests that the capture of dodecane droplets from the feed plays an important role in determining the overall rate of permeation. Other factors such as lower viscosity of the infused liquid, larger pore size, and higher operating pressure also improved the permeate flux through the LIMs. Overall, this work provides some guidelines on the design of composite membranes comprising infused liquids and the choice of operating conditions for the filtration process.

Switchable smart porous surface for controllable liquid transportation

Controllable liquid transportation through a smart porous membrane is realized by manipulating the surface wetting properties and external stimuli, and has been intensively studied. However, the liquid transportation, e.g., permeation and moving process, at the interface is generally uninterrupted, i.e., the opening and closing of the interface is irreversible. Herein, we present a new strategy to achieve magnetic adaptive switchable surfaces, i.e., liquid-infused micro-nanostructured porous composite film surfaces, for controllable liquid transportation, via modulation of the magnetic field. The liquid transportation process can be interrupted and restarted on the porous composite film because its pore structure can be quickly closed and opened owing to the adaptive morphological transformation of the magnetic liquid with a varying magnetic field. That is, the liquid permeation process occurs due to the open pore structure of the composite film when the external magnetic field is added, while the permeation process can be interrupted owing to the self-repairing closure of the pore when the magnetic field is removed, and the moving process can be achieved. Thus a magnetic field induced switchable porous composite film can serve as a valve to control liquid permeation based transportation, which opens new avenues for artificial liquid gating devices for flow, smart separation, and droplet microfluidics.

Sustainable Superhydrophobic Surface with Tunable Nanoscale Hydrophilicity for Water Harvesting

Fog collection can be a sustainable solution to water scarcity in many regions around the world. Recently, great efforts have been undertaken to develop low-cost and highly efficient water collectors to address water shortages, especially in arid regions. However, the design of a scalable water harvesting surface remains elusive to the trade-off between water deposition and transport. Herein, we developed a hydrophilic/superhydrophobic surface using a "one-pot" facile approach to enable an efficient water deposition and transport process. Preferential exposure of hydrophilic cellulose nanocrystal outer surface could be used to accelerate droplet deposition, coupled with wax microspheres with distinct wetting features for the manipulation of the droplet mobility. Appropriate tuning of the wetting characteristics of the surfaces, optimizing the hydrophobicity and density of the water affinity nanodomains allowed us to enhance the water deposition rate without the sacrifice of water transport. An optimal hydrophilic/superhydrophobic topography through the control of nanoscale hydrophilic and hydrophobic domains yielded a water harvesting flux of 3.402 L/m 2 /h for a plate and 5.02 L/m 2 /h for a mesh. This strategy of decorating a superhydrophobic surface with moderately hydrophilic nanodomains allows the manipulation of droplet nucleation and removal to enhance the water collection efficiency.

Cardamonin attenuates phorbol 12-myristate 13-acetate-induced pulmonary inflammation in alveolar macrophages

Pulmonary inflammation involves complex immune responses in which alveolar macrophages release pro-inflammatory proteins and cytokines. Cardamonin is a spice component that exerts anti-inflammatory and anti-oxidative properties against pulmonary inflammation. Herein, the aim of this research is to investigate the effects of cardamonin on pulmonary inflammation and its mechanism. Pulmonary inflammation in mice was induced by intratracheal administration of PMA. PMA-stimulated acute fibrosis, pulmonary edema, and inflammatory responses were ameliorated by oral administration of cardamonin in vivo. In MH-S alveolar macrophages, PMA-induced pro-inflammatory responses, including iNOS, COX-2, MMP-9 and cytokines expressions were reduced by cardamonin. The anti-oxidative Nrf2/HO-1 axis was also provoked by cardamonin in MH-S alveolar macrophages. In addition, MMP-9 expression induced by PMA is also decreased by the down-stream metabolites of HO-1, indicating that HO-1 expression partially contributes to the anti-inflammatory effect exerted by cardamonin. In this study, cardamonin demonstrates anti-inflammatory and anti-oxidative effects on PMA-induced pulmonary inflammation and activating Nrf2/HO-1 axis in alveolar macrophages. Cardamonin also ameliorates pulmonary inflammation, rapid fibrosis in vivo, suggesting powerful health benefits.

Multifunctional Switchable Nanocoated Membranes for Efficient Integrated Purification of Oil/Water Emulsions

Surfaces with unusual under-liquid dual superlyophobicity are attractive on account of their widespread applications, but their development remains difficult due to thermodynamic contradiction. Additionally, these surfaces may suffer from limited antifouling ability, which has restricted their practical applications. Herein, we report a successful in situ growth of a hybrid zeolitic imidazolate framework-8 and zinc oxide nanorod on a porous poly(vinylidene fluoride) membrane (ZIF-8@ZnO-PPVDF) and its application as a self-cleaning switchable barrier material in rapid filtration for emulsified oily wastewater. The novel ZIF-8@ZnO-PPVDF exhibits superior mechanical strength, reversible under-liquid dual superlyophobicity, photocatalytic self-cleaning property, and an effective alternate separation capacity toward both oil-in-water (O/W) and water-in-oil (W/O) emulsions with ultrahigh fluxes and efficiencies (>99%). By simply using a "bait-hook-eliminate" method to separate the O/W emulsions containing soluble organic pollutants, we demonstrate that the ZIF-8@ZnO-PPVDF can achieve stable separation fluxes over 600 L m^-2 h^-1 with high efficiencies and be completely/nondestructively regenerated by visible-light irradiation after each cycle. This study would demonstrate a new approach to prepare an under-liquid dual superlyophobic revivable membrane for various applications.

Abnormal Properties of Low-Dimensional Confined Water

Water molecules confined to low-dimensional spaces exhibit unusual properties compared to bulk water. For example, the alternating hydrophilic and hydrophobic nanodomains on flat silicon wafer can induce the abnormal spreading of water (contact angles near 0°) which is caused by the 2D capillary effect. Hence, exploring the physicochemical properties of confined water from the nanoscale is of great value for understanding the challenges in material science and promoting the applications of nanomaterials in the fields of mass transport, nanofluidic designing, and fuel cell. The knowledge framework of confined water can also help to better understand the complex functions of the hydration layer of biomolecules, and even trace the origin of life. In this review, the physical properties, abnormal behaviors, and functions of the confined water are mainly summarized through several common low-dimensional water formats in the fields of solid/air-water interface, nanochannel confinement, and biological hydration layer. These researches indicate that the unusual behaviors of the confined water depend strongly on the confinement size and the interaction between the molecules and confining surface. These diverse properties of confined water open a new door to materials science and may play an important role in the future development of biology.

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.

Superamphiphilic TiO2 Composite Surface for Protein Antifouling

Unwanted protein adsorption deteriorates fouling processes and reduces analytical device performance. Wettability plays an important role in protein adsorption by affecting interactions between proteins and surfaces. However, the principles of protein adsorption are not completely understood, and surface coatings that exhibit resistance to protein adsorption and long-term stability still need to be developed. Here, a nanostructured superamphiphilic TiO2 composite (TiO2 /SiO2 ) coating that can effectively prevent nonspecific protein adsorption on water/solid interfaces is reported. The confined water on the superamphiphilic surface enables a low adhesion force and the formation of an energy barrier that plays a key role in preventing protein adsorption. This adaptive design protects the capillary wall from fouling in a harsh environment during the bioanalysis of capillary electrophoresis and is further extended to applications in multifunctional microfluidics for liquid transportation. This facile approach is not only perfectly applied in channels with complicated configurations but may also offer significant insights into the design of advanced superwetting materials to control biomolecule adhesion in biomedical devices, microfluidics, and biological assays.

Super-spreading on superamphiphilic micro-organized nanochannel anodic aluminum oxide surfaces for heat dissipation

Nature-inspired superamphiphilic surfaces have drawn tremendous attention owing to its extreme liquid-loving behaviors. Herein, a micro-organized nano-channel (Mo-Na) superamphiphilic anodic aluminum oxide (AAO) surface with long-lasting superamphiphilic property is prepared by a facile one-step anodization method with controllable temperature change. Analysis of dynamic wetting behaviors on superamphiphilic Mo-Na AAO surfaces for various liquids reveals that the spreading factor is in negative correlation with the surface tension and liquid polarity. Detailed observation of the three-phase contact line shows a micro-scale capillary film on superamphiphilic Mo-Na AAO surfaces, which results from the horizontal component of the capillary force. Taking advantage of the superamphiphilic property, water droplets can spread completely on these Mo-Na AAO surfaces within a short time, which can be applied for efficient heat dissipation. Moreover, the unique AAO surface with Mo-Na structures also offers an effective template for future efforts in AAO-based composite devices.

Modulation of solid surface with desirable under-liquid wettability based on molecular hydrophilic-lipophilic balance

There has been great interest in the fabrication of solid surfaces with desirable under-liquid wettability, and especially under-liquid dual-lyophobicity, because of their potential for widespread use. However, there remains the lack of a general principle to modulate the under-liquid wettability in terms of surface energy (SE). Herein, we found that the relative proportion between the polar and dispersive components in SE that reflects the competition between hydrophilicity and lipophilicity governs the under-liquid wettability of the solid surface. For the first time, we introduced hydrophilic–lipophilic balance (HLB) calculated solely based on the amount and type of hydrophilic and lipophilic fragments in surface molecules to rapidly predict the under-liquid wettability of a solid surface, thereby guiding the fabrication of solid surfaces with desirable under-liquid wettability. Accordingly, the under-liquid dual superlyophobic surfaces in a nonpolar oil–water-solid system were fabricated by grafting molecules with appropriate HLB values (e.g., 6.341–7.673 in a cyclohexane–water–solid system) onto porous nanofibrous membranes, which were able to achieve continuous separation of oil–water mixtures. This work provides reasonable guidance for the fabrication of solid surfaces with targeted under-liquid wettability, which may lead to advanced applications in oil–water–solid systems.

Hydrophilic–lipophilic balance calculated based on the component of surface molecules is introduced to predict the under-liquid wettability of solid surfaces, thereby guiding the fabrication of solid surface with desirable under-liquid wettabilities.

Universal and tunable liquid-liquid separation by nanoparticle-embedded gating membranes based on a self-defined interfacial parameter

Superwetting porous membranes with tunable liquid repellency are highly desirable in broad domains including scientific research, chemical industry, and environmental protection. Such membranes should allow for controllable droplet bouncing or spreading, which is difficult to achieve for low surface energy organic liquids (OLs). Here we develop an interfacial physical parameter to regulate the OL wettability of nanoparticle-embedded membranes by structuring synergistic layers with reconfigurable surface energy components. Under the tunable solid-liquid interaction in the aggregation-induced process, the membranes demonstrate positive/negative liquid gating regularity for polar protic liquids, polar aprotic liquids, and nonpolar liquids. Such a membrane can be employed as self-adaptive gating for various immiscible liquid mixtures with superior separation efficiency and permeation flux, even afford successive achievement of high-performance in situ extraction-back extraction coupling. This study should provide distinctive insights into intrinsic wetting behaviors and have pioneered a rational strategy to design high-performance separation materials for diverse applications.

Crystal face dependent intrinsic wettability of metal oxide surfaces

Knowledge of intrinsic wettability at solid/liquid interfaces at the molecular level perspective is significant in understanding crucial progress in some fields, such as electrochemistry, molecular biology and earth science. It is generally believed that surface wettability is determined by the surface chemical component and surface topography. However, when taking molecular structures and interactions into consideration, many intriguing phenomena would enrich or even redress our understanding of surface wettability. From the perspective of interfacial water molecule structures, here, we discovered that the intrinsic wettability of crystal metal oxide is not only dependent on the chemical components but also critically dependent on the crystal faces. For example, the [Formula: see text] crystal face of α-Al2O3 is intrinsically hydrophobic with a water contact angle near 90°, while another three crystal faces are intrinsically hydrophilic with water contact angles <65°. Based on surface energy analysis, it is found that the total surface energy, polar component and Lewis base portion of the hydrophobic crystal face are all smaller than the other three hydrophilic crystal faces indicating that they have different surface states. DFT simulation further revealed that the adsorbed interfacial water molecules on each crystal face hold various orientations. Herein, the third crucial factor for surface wettability from the perspective of the molecular level is presented, that is the orientations of adsorbed interfacial water molecules apart from the macro-level chemical component and surface topography. This study may serve as a source of inspiration for improving wetting theoretical models and designing controllable wettability at the molecular/atomic level.

Charge-Enhanced Separation of Organic Pollutants in Water by Anionic Covalent Organic Frameworks

The effective removal of organic pollutants in wastewater is a key environmental challenge. In this work, an anionic covalent organic framework (named TpPa-SO₃Na) was synthesized through a green two-in-one synthesis strategy with autocatalytic imine formation. The slowly generated acetic acid as a catalyst is favorable to sustain the reversibility of the covalent organic framework (COF) formation reaction and improve the crystallinity of TpPa-SO₃Na. TpPa-SO₃Na consists of a homogeneous distribution of sulfonate groups to produce negatively charged regular channels. The strong electrostatic and hydrogen-bonding interactions between the sulfonate groups anchored in the nanochannels and the amine groups in organic pollutants improve the adsorption selectivity and capacity. These structures allow a high degree of control over adsorption processes to boost the adsorption kinetics and improve selective separation. TpPa-SO₃Na exhibits ultrafast adsorption (<1 min) of cationic antibiotics and dyes (average over 95%). Furthermore, TpPa-SO₃Na exhibits high selectivity for the uptake of dye molecules on the basis of the differences in charge and molecular size. This work explored functional designs and green manufacturing of anionic COFs for removal of hydrophilic organic pollutants.

Simulation Study on the Dynamic Behaviors of Water-in-Oil Emulsified Droplets on Coalescing Fibers

Although increasing superwetting membranes have been developed for separating oil-water emulsions based on the "size-sieving" mechanism, their pores are easily blocked and fouled by the intercepted emulsified droplets, which would result in a severe membrane fouling issue and a sharp decline in flux. Instead of droplet interception, a fiber-based coalescer separates oil/water emulsions by inducing the emulsified droplets to coalesce and transform into layered oil/water mixtures, exhibiting an ability to work continuously for a long time with high throughput, which makes it a promising technology for emulsion treatment. However, the underlying mechanism of the separation process is not well understood, which makes it difficult to further improve the separation performance. Hence, in this work, the dynamic behaviors of water-in-oil emulsified droplets on the surface of the coalescing fiber were numerically investigated based on the phase-field model. The attachment, transport, and detachment behaviors of droplets on fibers were directly observed, and the effects of fiber wettability, orientation, arrangement, and fluid speed were studied in detail. First, it was observed that the droplets will move downstream along the fiber surface under the effect of fluid shear, and the large droplets tend to coalesce with their downstream small droplets on the same fiber surface because they move faster compared to the small droplets. Second, it was found that the emulsified droplet will spontaneously transport to the intersection of two angled fibers under the drive of asymmetric Laplace pressure, which demonstrated that the emulsified droplets tend to gather at the intersection of fibers when permeating through a coalescing medium. Third, it was found that the detachment behaviors of droplets from the fiber surface are strongly affected by their size, fiber wettability, and fluid velocity. In addition, the results of our simulation show that the backside of two closely attached fibers can further inhibit the detachment of droplets. We truly believe that our research results are of significance to optimize the parameters of a fiber-based coalescer for separating oil-water emulsions and to develop novel oil/water separators.