Synergistic Construction of Superhydrophilic PVDF Membranes by Dual Modification Strategies for Efficient Emulsion Separation.

Solving the problem of oil and water pollution is an important topic in environmental protection. The separation of oil-water emulsion with high efficiency and low consumption has been the direction of social efforts. Membrane separation technology combined with surface wettability and pore size screening is considered to be one of the most promising ways to separate oil-water emulsions. In this paper, the polyvinylidene difluoride (PVDF) membrane is prepared by combining the two methods of blending and coating modification as a double barrier. The prepared PVDF membrane can completely wet water, achieve superhydrophilic in air, and superoleophobic underwater. The separation efficiency and flux are 99.57% and 678 L h-1 m-2 bar-1, respectively, for toluene emulsions containing surfactants with an average particle size of 1.7 µm. At the same time, it can also effectively separate different kinds of light/heavy oils. After three cycles of testing still maintain high efficiency of separation. The results show that the prepared PVDF membrane can effectively separate the emulsion containing surfactant with smaller particle size distribution of oil droplets. This method provides a new strategy for the separation of oil-water emulsions and has broad application prospects.

Biomimetic Superwetting Fabric for Evaporation-Induced Body Sweat and Heat Management and Electricity Generation.

Solar optothermal evaporation of water possesses the potential for thermal regulation and electricity generation, which are desirable for regulating body perspiration and heat as well as improving electrical output and strain sensing. However, ordinary fabrics exhibit poor evaporation capacity and antifouling performance due to limited adsorption capacity and internal hydrophilicity. Moreover, conventional evaporation-driven generators show a low power supply without widely practical use due to limited and fluctuating evaporation rates. Herein, an antifouling cooling fabric with an evaporation-driven electricity performance is obtained by constructing Janus channels on the superomniphobic fabric. Sweat can be easily eliminated from inside to outside through Janus channels by efficient evaporation, and the green liquid metal ink (CGM/LMP-rGO@PPy) cotton fabric shows a thermal conductivity of 0.18 W m-1 K-1, suggesting a comfortable dry and cooling sense. Meanwhile, the fabric can stably output a potential of 302.20 mV when seawater flows through the ionic channels at an evaporation rate of 1.58 mL h-1 with one sun power density. In addition, the multifunctional fabric demonstrates strain sensing at high electrical conductivity for body motion monitoring. This work would offer a prospect for intelligent textile construction and energy harvesting by water evaporation.

Efficient Water Mist Collector with Both a Kirigami Structure and Chemical Modification.

The shortage of freshwater resources is a common problem faced by people all over the world. Water mist collection provides a feasible solution to this problem. In this paper, three kinds of foggers with a kirigami structure and chemical modification were prepared. Their fog collection efficiencies were 3.04, 3.17, and 3.54 g·h-1·cm-2, respectively, which were 1.57, 1.63, and 1.82 times that of the original zinc sheet. Then, the fog collector of sample 3 with the highest fogging efficiency was analyzed and discussed. In order to evaluate the practical application of the sample, durability and ultraviolet (UV) resistance tests of the sample were carried out. The experimental results show that the surface of sample 3 has better durability and excellent UV resistance. In addition, the fog collector design incorporating readily available materials and a straightforward preparation process showcases outstanding efficiency. As such, it presents a novel approach for the development of high-performance fog collection systems in the future.

Janus Fabric with Asymmetric Wettability for Switchable Emulsion Separation and Controllable Droplets with Low Friction.

Superwetting surfaces have recently attracted extensive attention in oil-water emulsion separation and droplet manipulations, which are widely used in various situations ranging from wastewater treatment, to flexible electronics, to biochemical diagnosis. However, it still remains challenging to obtain asymmetric materials with high efficiency during oil-water separation. Meanwhile, excellent robustness of the superhydrophobic surface is of significance but retards the mobility of droplets due to increased lateral adhesion of small spacing between solid protrusions. Herein, a facile approach is demonstrated to obtain the excellent robustness of Janus fabrics with asymmetric wettability. As for one side of water-in-oil emulsion separation, mimicking the soft earthworm with periodically wrinkled skin, an adaptive superhydrophobic fabric was fabricated by wrapping soft wrinkled poly(dimethylsiloxane) (PDMS) polymer with a cross-linking structure on woven fabric fibers induced by Ar plasma treatment. In addition, inspired by the desert beetle's structure but with reversed wettability, the other side of the Janus fabric was constructed for treating emulsion of oil-in-water. In addition, the underwater superoleophobic surface consisting of magnetically responsive PDMS microcilia with slippery heads, which shows robustness against pH, improved water drop mobility and lowered the resistance of fluid friction similar to the intrinsic hydrophobic Salvinia molesta with additional slippery performance. Hence, we propose a novel and easy approach that optimizes enhanced emulsion separation and reduced fluid drag properties simultaneously, which actively broadens their widespread applications.

Underwater Superoleophobic and Underoil Superhydrophilic Copper Benzene-1,3,5-tricarboxylate (HKUST-1) Mesh for Self-Cleaning and On-Demand Emulsion Separation.

Surfaces with underoil superhydrophilic (UOSHL) and underwater superoleophobic (UWOHB) have great potential for on-demand emulsion separation. However, the fabrication of underoil superhydrophilic based on wetting thermodynamic principles is quite challenging. Several previous studies have shown that some sarcocarps are able to spontaneously absorb water to moisturize themselves and have a unique UOSHL ability. By mimicking this unique ability of the sarcocarp, an outstanding UWOHB and UOSHL membrane was prepared. We choose 2300 mesh stainless steel mesh (SSM) as the substrate, then grow Cu and Cu(OH)2 on SSM by a simple electrochemical method, and finally grow HKUST-1 crystals via a fast in situ growth method. The whole preparation process is simple, low cost, and does not require complex and long-term hydrothermal reactions. By growing HKUST-1 crystals, the prepared surface successfully achieved the required UOSHL and UWOHB properties. When the water droplets come into contact with the membrane under n-hexane, it will diffuse and can completely spread out in 2 s. The as-prepared membrane exhibits outstanding anti-fouling and self-cleaning properties for rapeseed oil and crude oil with high viscosity underwater due to the special wetting. By prewetting the surface with an appropriate amount of the dispersion medium, it can rapidly and efficiently on-demand separate different emulsions. The separation efficiencies of water-in-oil emulsions and oil-in-water emulsions are above 99.00 and 97.00%. With their outstanding performance in self-cleaning, on-demand emulsion separation, low cost, and fast preparation, the as-prepared UOSHL and UWOHB HKUST-1 meshes show excellent potential for treating oily wastewater in practical applications.

Robust Superamphiphobic Coating Applied to Grease-Proof Mining Transformer Components.

The iron core and heat sink in a mining transformer are susceptible to damage from oil spills or the harsh mine environment; the deterioration of oil products in the underground environment and transformers produce massive amounts of harmful liquid substances, which may lead to unnecessary economic losses in drilling engineering. To overcome this issue, a convenient and economical way to protect transformer components was developed. Herein, we proposed an air spray technology at room temperature for the preparation of antigreasy superamphiphobic coatings, which are suitable for bulk metallic glass transformer cores and ST13 heat sinks. The addition of polypyrrole powder effectively improves the thermal conductivity and specific heat of the coating in the range of 50-70 °C. More importantly, the fabricated coating has excellent repellency to liquids, such as water, ethylene glycerol, hexadecane, and rapeseed oil. Meanwhile, the coating has excellent physical and chemical resistance and outstanding antifouling features, which provide a feasible solution for combating grease pollution and corrosion in the mine environment. Taking multifaceted stability into consideration, this work contributes to enhancing the application of superamphiphobic coatings in the fields of protecting transformer components in the harsh environment or during transformer operation faults.

High-Performance Magnetic and Electric Control of Liquid Metal Droplets.

In the present study, we propose a magnetically controlled and electrically controlled magnetic liquid metal (MLM) method to achieve high-performance multiple manipulation of droplets. The prepared MLM has good active and passive deformability. Under the action of the magnetic field, controllable transport, splitting, merging, and rotation are realized. In addition, controllable electric field manipulation in alkaline and acidic electrolytes is realized. This simple preparation method can be applied to the precise and rapid control of the magnetic field and electric field at the same time. Compared with other droplet manipulation methods, we realized droplet manipulation independent of special surfaces. It has the advantages of easy implementation, low cost, and high controllability. It shows great application potential in the fields of biochemical analysis, microfluidics, drug transportation in complex limited space, and intelligent soft robots.

Robust Janus Superwetting Textile with Large Pore Sizes for Oil-in-Water Emulsion Separation.

Developing advanced oil-water separation technology is significant for environmental conservation. According to the synergetic effects of the size-sieving mechanism, superwetting materials with small pore sizes have been designed to realize high-efficiency separation for oil-water emulsions. However, the separation flux limited by the pore size and the weakness of the superwetting material impede its practical application severely. Herein, we construct a robust Janus superwetting textile with large pore sizes for oil-in-water emulsion separation. The pristine textile is coated by the as-prepared CuO nanoparticles as the bottom layer with superhydrophilicity and then grafted by 1-octadecanethiol as the top layer with superhydrophobicity to construct the Janus textile. When used as a filter, the superhydrophobic layer acts as the nucleation site to coalesce the small oil droplets facilely. Then, the coalesced oil fills the pores of the superhydrophobic layer and selectively permeates it but is blocked by the superhydrophilic layer with large pore sizes. Utilizing the unique separation mechanism, the Janus textile realizes efficient and rapid separation. Even after multicycle separation, hot liquid immersion for 24 h, tribological test for 60 min, and sandpaper abrasion for 500 cycles, the Janus textile still retains the superwettability and excellent separation performance, manifesting outstanding stability to resist severe damage. This separation strategy provides a novel guideline for high-efficiency and high-flux emulsion separation and practical application.

High-breathable, antimicrobial and water-repellent face mask for breath monitoring.

Face masks with multiple functionalities and exceptional durability have attracted increasing interests during the COVID-19 pandemic. How to integrate the antibacterial property, comfortability during long-time wearing, and breath monitoring capability together on a face mask is still challenging. Here we developed a kind of face mask that assembles the particles-free water-repellent fabric, antibacterial fabric, and hidden breath monitoring device together, resulting in the highly breathable, water-repellent, and antibacterial face mask with breath monitoring capability. Based on the rational design of the functional layers, the mask shows exceptional repellency to micro-fogs generated during breathing while maintaining high air permeability and inhibiting the passage of bacteria-containing aerogel. More importantly, the multi-functional mask can also monitor the breath condition in a wireless and real-time fashion, and collect the breath information for epidemiological analysis. The resultant mask paves the way to develop multi-functional breath-monitoring masks that can aid the prevention of the secondary transmission of bacteria and viruses while preventing potential discomfort and face skin allergy during long-period wearing.

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

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

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.

Cellulose/Poly(vinyl alcohol)/Tannic Acid Porous Cross-Linked Composite Frame Materials with Excellent Oil/Water Separation Performance.

Problems such as increasingly serious water pollution attracted widespread concern. The underwater OCAs of the samples became larger with increasing pH and the under-oil WCAs of the samples did not vary regularly with increasing pH. Nanoneedle structures were grown on metal foam by anodization. Cellulose is fixed to the frame by cross-linking with supramolecular binder poly(vinyl alcohol)/tannin. A cellulose/poly(vinyl alcohol)/tannin porous composite framework with special wettability is prepared. This porous composite framework can be used for the continuous separation of oil/water mixtures with high separation efficiency, high throughput, excellent reusability, and mechanical durability. In addition, due to the coating of cellulose and the supramolecular binder, the pore size of the frame is reduced, and the cagelike structure of the porous framework can promote its demulsification effect. Therefore, the cellulose/poly(vinyl alcohol)/tannic acid porous composite frame can also be used for the separation of oil/water emulsions. This porous frame material has broad application prospects in oil spill treatment and sewage purification.

Asymmetric Robust Superhydrophobic/Superhydrophilic Janus Membranes for the Moisture Proofing of Oil and Purification of Water.

The performance degradation of oil caused by moisture and water pollution induced by the infiltration of oil can result in huge losses for society. This is especially true of stable emulsified mixtures of oil and water, which are difficult to separate and urgently require a processing method. In this work, a robust Janus membrane prepared by combining simple electrodeposition and spraying processes was used to separate water-in-transformer oil/lubricating oil emulsions and various oil-in-water emulsions. The membrane with outstanding separation efficiency was also endowed high flux to emulsions, even after 10 separation cycles and 100 sand impact tests, indicating that separation ability was retained. Furthermore, the excellent resistance to acidic and alkaline liquids of the superhydrophobic side groups of the membrane increased the possibility of its service in harsh environments. This study's findings reveal great potential regarding the expansion and application of oil-water separation materials.

Durable 3D Porous Superhydrophobic Composites for Versatile Emulsion Separation in Multiple Environments.

Polydopamine as a multifunctional biomimetic polymer with nonselective strong adhesion properties has become a hot research topic in recent years. However, there are a few reports on the durable and effective emulsion separation of polydopamine composites from other materials. Therefore, it is necessary to construct durable polydopamine composites to achieve selective adsorption of materials. In this work, polypyrrole (PPy)-PDA was obtained on sponges by an in situ polymerization reaction, followed by the attachment of SiO2 nanoparticles to the surface by polydimethylsiloxane to achieve superhydrophobicity. As a result, previously unreported selective superhydrophobic adsorbents for PPy-PDA coatings were obtained. The prepared sponges have an excellent adsorption capacity for oils and organic solvents. Not only can the sponges absorb 19-39 g of organic solvents per gram but they can also absorb oil from oil-in-water emulsions. The chemical oxygen demand value of the emulsion can be reduced to 219 mg/L after separation. More importantly, the performance remains good in the cycle test, and due to the construction of a durable superhydrophobic sponge, it can still maintain its relatively good performance in artificial seawater, acid-base environments, and can achieve relatively stable emulsion separation. At the same time, the potential of the polymer material composited with PDA in lasting and stable emulsion separation was also verified.

How to Efficiently Prepare Transparent Lubricant-Infused Surfaces: Inspired by Candle Soot.

Poly(dimethylsiloxane) is a common dispersant, modifier, and binder in the field of bioinspired wettability. Herein, the soot production when poly(dimethylsiloxane) was burning was used to directly construct a superhydrophobic coating with the water contact angle reaching 159.7°. After the lubricant was infused, its transparency was greater than 80% of air in the visible light range of the human eye. In addition, the sliding angle and contact angle of the coating were stable for 15 days. It showed excellent oil-locking ability and stability. Even if the superhydrophobic coating was immersed in various organic solvents for 15 days, its hydrophobicity did not change. Moreover, the coating had an excellent anti-fouling ability and self-cleaning ability to meet actual application conditions. Furthermore, the preparation method was simple and rapid, without the participation of fluorine-containing modifiers, and provides a brand-new method for preparing transparent lubricant-infused surfaces.

Multifuctional Janus Materials for Rapid One-Way Water Transportation and Fog Collection.

A novel micronano wire channels Janus membrane (WCJM) was fabricated by a convenience spraying method. We prepared a series of samples with different (super)hydrophobic energy barriers and studied the effects of WCJMs on one-way transportation and fog collection. The droplets can be one-way transported from the (super)hydrophobic side to the superhydrophilic side, forming a transport channel when they contact the superhydrophilic micronano wire under hydrostatic pressure. In the experiment, when droplets touch the exposed micronano wires, they will be rapidly absorbed by the superhydrophilic side. However, when the superhydrophobic energy barrier is thick and the superhydrophobic layer completely covers the micronano wires on the substrate surface, the droplets cannot achieve one way transport behavior. Besides, we observed three different fog collection modes. They have a significant difference in fog collection efficiency. In WCJM-3, the superhydrophobic side collects fog in a dropwise condensation mode, and then transported to the superhydrophilic side through the micronano wire channels for storage, with the highest fog collection efficiency (1.1 g/cm2·h). The results show that the WCJM surface not only makes full use of the difference in wettability and micronano wire structure to promote the droplets one-way transportation, but also improves the fog collection performance by accelerating surface regeneration, which has potential application value in fog collection, droplet treatment and related engineering.

Simple Method for the Fabrication of Multiple Superwetting Surfaces with Photoresponse.

There have been many studies on special wetting surfaces, but most of them just stay superlyophobic in air or underwater. In this work, a membrane with photoresponse is fabricated by spraying hybrid particles of silicon and titanium dioxide. Under the combined action of hybrid particles and 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, the prepared membrane is superhydrophobic in air. Because of the presence of titanium dioxide, the membrane can realize the transformation from superoleophilic underwater to superoleophobic underwater through UV irradiation and heating. Surprisingly, the membranes with superoleophobicity underwater are also superhydrophobic underoil. Thanks to this unique wettability transition, the prepared membrane can be applied to emulsion separation and fog harvesting. This is inspiring for the preparation and the multifunctional application of multiphase media superlyophobic surfaces.

Artificial Leaf for Switchable Droplet Manipulation.

Droplet manipulation plays an important role in scientific research, daily life, and practical production such as biological and chemical analysis. Inspired by the structure and function of three typical leaf veins, the bionic texture was replicated by the template method, and the artificial leaf was selectively treated by nanoparticles to obtain a quasi-three-dimensional hybrid superhydrophobic-hydrophilic surface. When the droplet touches the surface of the leaf, it will be attracted to the bottom of the main vein from different directions even in horizontal conditions due to the Laplace pressure gradient and energy gradient. The simulation analysis demonstrates that the reason for directional transportation is the energy gradient of the droplets on the different levels of veins, including the thin veins, lateral veins, and main vein. Meanwhile, the experimental result of water collection also showed an outstanding directional transportation effect and excellent water collection efficiency. In addition, when the sample is tilted upside down, the droplet will flow back to the main vein along the lateral vein and then flow down the main vein, showing a good droplet pumping effect. Therefore, the directional and polydirectional transportation of droplets on the same sample is successfully realized, and the conversion between executing single and multiple tasks simultaneously can be realized only by upright and inverted samples. This work provided a new strategy for directional and polydirectional water manipulation, water collection, directional drainage, and microfluidic devices.

Adhesion behaviors on four special wettable surfaces: natural sources, mechanisms, fabrications and applications.

The study of adhesion behaviors on solid-liquid surfaces plays an important role in scientific research and development in various fields, such as medicine, biology and agriculture. The contact angle and sliding angle of the liquid on the solid surface are commonly used to characterize and measure the wettability of a particular surface. They have a wide range of values, which results in different wettability. It boils down to the adhesion of solid surfaces to liquids. This feature article is aimed at revealing the essence of the adhesion behavior from the aspects of controlling the chemical composition or changing the geometrical microstructure of the surface, and reviewing the natural sources, wetting models, preparation methods and applications of four kinds of typical solid-liquid surfaces (low-adhesion superhydrophobic surfaces, high-adhesion superhydrophobic surfaces, slippery liquid-infused porous surfaces (SLIPS) and hydrophilic/superhydrophilic surfaces). Last, a summary and outlook on this field are given to point out the current challenges and the potential research directions of surface adhesion in the coming future.

Facile Fabrication of Slippery Lubricant-Infused CuO-Coated Surfaces with Different Morphologies for Efficient Water Collection and Excellent Slippery Stability.

How to prepare multifunctional surfaces with high nucleation density and fast droplet removal during droplet condensation remains a challenge. It is believed that a water droplet on a superhydrophobic surface (SHS) in the Cassie state is inclined to convert to the Wenzel state under high-pressure or high-humidity conditions, which results in the pinning effect. Hence, it is necessary to form thermodynamically stable lubricant-infused surfaces (LISs) to be applied in water condensation, especially under extreme working conditions. In this work, CuO LISs with two different morphologies (chrysanthemum-like and dandelion-like structures) in the slippery state were prepared and the effect of surface morphology on water harvesting behavior was investigated. The results indicated that dandelion-like CuO consisting of nanoneedles exhibited inferior water harvesting behavior compared to chrysanthemum-like CuO consisting of nanolamellas due to worse lubricating oil loss. Furthermore, the strong intermolecular forces between the perfluoropolyether (PFPE) lubricating oil and perfluorodecanethiol (PFDT)-modified coating resulted in a durable lubricating layer, which exhibited favorable anti-icing, anticorrosion, and liquid repellency even under strong acid and alkali conditions, high shear force rate up to 7000 rpm, and long-time ultraviolet light irradiation for 12 h. This work paves the path for efficient droplet nucleation and removal, which has potential in water harvesting in arid regions and water condensation for power generation.