Generalized Multifunctional Coating Strategies Based on Polyphenol-Amine-Inspired Chemistry and Layer-by-Layer Deposition for Blood Contact Catheters

Blood-contacting catheters play a pivotal role in contemporary medical treatments, particularly in the management of cardiovascular diseases. However, these catheters exhibit inappropriate wettability and lack antimicrobial characteristics, which often lead to catheter-related infections and thrombosis. Therefore, there is an urgent need for blood contact catheters with antimicrobial and anticoagulant properties. In this study, we employed tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) to create a stable hydrophilic coating under mild conditions. Heparin (Hep) and poly(lysine) (PL) were then modified on the TA-APTES coating surface using the layer-by-layer (LBL) technique to create a superhydrophilic TA/APTES/(LBL)4 coating on silicone rubber (SR) catheters. Leveraging the superhydrophilic nature of this coating, it can be effectively applied to blood-contacting catheters to impart antibacterial, antiprotein adsorption, and anticoagulant properties. Due to Hep's anticoagulant attributes, the activated partial thromboplastin time and thrombin time tests conducted on SR/TA-APTES/(LBL)4 catheters revealed remarkable extensions of 276 and 103%, respectively, when compared to uncoated commercial SR catheters. Furthermore, the synergistic interaction between PL and TA serves to enhance the resistance of SR/TA-APTES/(LBL)4 catheters against bacterial adherence, reducing it by up to 99.9% compared to uncoated commercial SR catheters. Remarkably, the SR/TA-APTES/(LBL)4 catheter exhibits good biocompatibility with human umbilical vein endothelial cells in culture, positioning it as a promising solution to address the current challenges associated with blood-contact catheters.

Design and Machine Learning Prediction of In Situ Grown PDA-Stabilized MOF (UiO-66-NH2) Membrane for Low-Pressure Separation of Emulsified Oily Wastewater

Significant progress has been made in designing advanced membranes; however, persistent challenges remain due to their reduced permeation rates and a propensity for substantial fouling. These factors continue to pose significant barriers to the effective utilization of membranes in the separation of oil-in-water emulsions. Metal-organic frameworks (MOFs) are considered promising materials for such applications; however, they encounter three key challenges when applied to the separation of oil from water: (a) lack of water stability; (b) difficulty in producing defect-free membranes; and (c) unresolved issue of stabilizing the MOF separating layer on the ceramic membrane (CM) support. In this study, a defect-free hydrolytically stable zirconium-based MOF separating layer was formed through a two-step method: first, by in situ growth of UiO-66-NH2 MOF into the voids of polydopamine (PDA)-functionalized CM during the solvothermal process, and then by facilitating the self-assembly of UiO-66-NH2 with PDA using a pressurized dead-end assembly. A stable MOF separating layer was attained by enriching the ceramic support with amines and hydroxyl groups using PDA, which assisted in the assembly and stabilization of UiO-66-NH2. The PDA-s-UiO-66-NH2-CM membrane displayed air superhydrophilicity and underwater superoleophobicity, demonstrating its oil resistance and high antifouling behavior. The PDA-s-UiO-66-NH2-CM membrane has shown exceptionally high permeability and separation capacity for challenging oil-in-water emulsions. This is attributed to numerous nanochannels from the membrane and its high resistance to oil adhesion. The membranes showed excellent stability over 15 continuous test cycles, which indicates that the developed MOFs separating layers have a low tendency to be clogged by oil droplets during separation. Machine learning-based Gaussian process regression (GPR) models as nonparametric kernel-based probabilistic models were employed to predict the performance efficiency of the PDA-s-UiO-66-NH2-CM membrane in oil-in-water separation. The outcomes were compared with the support vector machine (SVM) and decision tree (DT) algorithm. This efficiency includes various metrics related to its separation accuracy, and the models were developed through feature engineering to identify and utilize the most significant factors affecting the membrane's performance. The results proved the reliability of GPR optimization with the highest prediction accuracy in the validation phase. The average percentage increase of the GPR model compared to the SVM and DT model was 6.11 and 42.94%, respectively.

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

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

Transparent and Superhydrophilic Flexible Protein Films with Antifogging and Self-Cleaning Attributes

Cyanoglycoside-modified flexible protein films, exhibiting a high level of transparency of ≈46 to 83%, were successfully prepared from lysozyme and glycerol with varying amounts of amygdalin (20, 40, and 60%) using water as a solvent. The increasing percentage of amygdalin leads to a drastic improvement of the hydrophilicity of the surface with a decrease in the water contact angle to 5.6°, resulting in superhydrophilicity. The increasing percentage of amygdalin led to a significant improvement in the surface's hydrophilicity, resulting in a reduced water contact angle of 5.6° and achieving superhydrophilicity. This superhydrophilic characteristic is particularly relevant to the excellent antifogging and self-cleaning properties of the resulting protein films. In addition to enhanced flexibility, the films also exhibited considerably improved thermal stability with a 40% loading of amygdalin in the protein solution. The superior mechanical, optical, and thermal properties of amygdalin-modified films are due to the strong hydrogen bonding with the peptides of lysozyme, as evidenced by the disappearance of amide bands in the cured protein films. Therefore, these transparent protein films, with their antifogging and enhanced thermal stability properties, can be potentially used for different packaging and coating applications.

Super-Fast Fog Collector Based on Self-Driven Jet of Mini Fog Droplets

Freshwater scarcity crisis threatens human life and economic security. Collecting water from the fog seems to be an effective method to defuse this crisis. Nonetheless, the existing fog collection methods have the limitations of the low fog collection rate and efficiency because of their gravity-based droplet shedding. Here, the aforementioned limitations are resolved by proposing a new fog collection method based on the self-driven jet phenomenon of the mini fog droplets. A prototype fog collector (PFC) composed of a square container that is filled with water is first designed. Both sides of the PFC are superhydrophobic but covered with superhydrophilic pore array. The mini fog droplets touching the side wall are easily captured and spontaneously and rapidly penetrate into the pores to form jellyfish-like jets, which greatly increases the droplet shedding frequency, guaranteeing a higher fog collection rate and efficiency compared with the existing fog collection methods. Based on this, a more practical super-fast fog collector is finally successfully designed and fabricated which is assembled by several PFCs. This work is hoping to resolve the water crisis in some arid but foggy regions.

Droplet-Driven Self-Propelled Devices Fabricated by a Femtosecond Laser

Self-propelled autonomous devices have broad application prospects in energy conservation, environmental protection, and biomedical engineering. Nevertheless, the driving force always consumes external energy or special chemicals. Here, a novel and green droplet-driven device (DDD) consisting of superhydrophilic triangles on a superhydrophobic plate is processed only by a femtosecond laser. The water droplet flows into water along the superhydrophilic channel and forms a jet to provide driving force for the DDD, whose strength can be manipulated by changing the point angle of the triangle and the volume of the droplet. By fabricating multiple or special channels, the DDD can translate and rotate along the designed track and even carry objects. This provides a new route for the fabrication of green self-propelled autonomous devices and their applications in the fields of intelligent systems and environmental protection.

Magnetically Actuated Superhydrophilic Robot Sphere Fabricated by a Femtosecond Laser for Droplet Steering

Droplet steering has important applications in biomedical detection, local chemical reactions, liquid collection, and microfluidic control. Presently, droplet steering methods typically require specific paths and can be challenging to operate, involving complex fabrications for the operating systems. Here, we show a magnetically actuated superhydrophilic robot sphere (MSR) based on femtosecond laser direct writing technology for droplet steering. Through femtosecond laser treatment, uniform micro-/nanostructures are constructed on the surface of a MSR. Additionally, the contactless magnetic actuator makes it possible to remotely steer the MSR to transport droplets. After preliminary exploration of the mechanism by which MSR drives the droplet movement, the ability of MSR to control the droplet movement was systematically tested and analyzed. Moreover, the applications of the MSR in complex path liquid collection and transport, three-dimensional space transport, self-cleaning, etc., are further verified. This strategy provides a novel and reliable path for droplet manipulation and broadens its application.

Designing Versatile Superhydrophilic Structures via an Alginate-Based Hydrophilic Plasticene

The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart liquid manipulation in both research and application fields. To design versatile superhydrophilic interfaces with various structures, here we introduce a hydrophilic plasticene that possesses high flexibility, deformability, water absorption, and crosslinking capabilities. Through a pattern-pressing process with a specific template, 2D prior fast spreading of liquids at speeds up to 600 mm/s was achieved on the superhydrophilic surface with designed channels. Additionally, 3D superhydrophilic structures can be facilely designed by combining the hydrophilic plasticene with a 3D-printed template. The assembly of 3D superhydrophilic microstructure arrays were explored, providing a promising route to facilitate the continuous and spontaneous liquid transport. The further modification of superhydrophilic 3D structures with pyrrole can promote the applications of solar steam generation. The optimal evaporation rate of an as-prepared superhydrophilic evaporator reached ~1.60 kg·m^-2·h^-1 with a conversion efficiency of approximately 92.96%. Overall, we envision that the hydrophilic plasticene should satisfy a wide range of requirements for superhydrophilic structures and update our understanding of superhydrophilic materials in both fabrication and application.

Improved Liquid Collection on a Dual-Asymmetric Superhydrophilic Origami

Manipulating fluid with an open channel provides a promising strategy to simplify the current systems. Nevertheless, spontaneous on-surface fluid transport with large flux, high speed, and long distance remains challenging. Inspired by scallop shells, here a shell-like superhydrophilic origami (S-SLO) with multiple-paratactic and dual-asymmetric channels is presented to improve fluid collection. The origami channel can capture various types of liquids, including droplets, flow, and steam, and then transport collected liquid unidirectionally. The S-SLO with 2 mm depth can reach maximum flux of 450 mL h^-1 , which is five times the capacity of a flat patterned surface with similar dimension. To diversify the function of such interface, the SLO is further integrated with a superhydrophobic zirconium carbide/silicone coating for enhanced condensation via the collaboration of directional fluid manipulation and a radiative cooling layer. Compared with the unmodified parallel origami, the shell-like origami with a radiative cooling layer shows a 56% improvement in condensate efficiency as well as the directional liquid drainage. This work demonstrates a more accessible design for the optimization of on-surface fluid control, and the improved performance of liquid transport should extend the applications of bioinspired fluid-manipulating interfaces.

Facile Fabrication of Superwetting PVDF Membrane for Highly Efficient Oil/Water Separation

A novel superhydrophilic and underwater superoleophobic modified PVDF membrane for oil/water separation was fabricated through a modified blending approach. Pluronic F127 and amphiphilic copolymer P (MMA-AA) were directly blended with PVDF as a hydrophilic polymeric additive to prepare membranes via phase inversion induced by immersion precipitation. Then, the as-prepared microfiltration membranes were annealed at 160 °C for a short time and quenched to room temperature. The resultant membranes exhibited contact angles of hexane larger than 150° no matter whether in an acidic or basic environment. For 1, 2-dichloroethane droplets, the membrane surface showed a change from superoleophilic to superoleophobic under water with aqueous solutions with pH values from 2 to 13. This as-prepared membrane has good mechanical strength and can then be applied for oil and water mixture separation.

Superhydrophilic Modification of Polyvinylidene Fluoride Membrane via a Highly Compatible Covalent Organic Framework-COOH/Dopamine-Integrated Hierarchical Assembly Strategy for Oil-Water Separation

The integration of membranes with additives such as functionalized nanomaterials can be recognized as an effective method to enhance membrane performance. However, to obtain an efficient nanoparticle-decorated membrane, the compatibility of nanomaterials remains a challenge. Hydrophilic carboxylated covalent organic frameworks (COF-COOH) might be expected to avoid the drawbacks of aggregation and easy shedding of inorganic materials caused by the poor interfacial compatibility. Herein, a highly compatible dip-coating strategy was proposed for the superhydrophilic modification of polyvinylidene fluoride membrane via COF-COOH integrated with dopamine. COF-COOH together with polydopamine nanoparticles were uniformly and stably attached to the membrane due to the high interfacial compatibility, constructing a coating with rough hierarchical nanostructures and abundant carboxyl groups. The synergistic effects of multiscale structures and chemical groups endow the membrane with superhydrophilicity and underwater superoleophobicity, the water contact angle decreased from 123 to 15°, and the underwater oil contact angle increased from 132 to 162°. Accordingly, the modified membrane exhibits an ultrahigh oil rejection ratio (>98%), a high flux (the maximum reaches 1843.48 L m^-2 h^-1 bar^-1), attractive antifouling ability, and impregnable stability. This work would provide a momentous reference for the application of COF-COOH in practical oily wastewater treatment.

Fast Capture, Collection, and Targeted Transfer of Underwater Gas Bubbles Using Janus-Faced Carbon Cloth Prepared by a Novel and Simple Strategy

Transportation of bubbles in liquids in a controlled fashion is a challenging task and an important subject in numerous industrial processes, including elimination of corrosive gas bubbles in fluid transportation pipes, water electrolysis, reactions between gases, heat transfer, etc. Using superaerophilic surfaces represents a promising solution for bubble movement in a programmed way. Here, a novel and low-cost method is introduced for the preparation of Janus-faced carbon cloth (Janus-CC) using poly(dimethylsiloxane) (PDMS) coating and then burning one side of the carbon cloth/PDMS on an alcoholic burner. The results show that the superhydrophobic face behaves as a superaerophilic surface, while the superhydrophilic side is aerophobic underwater. Subsequently, the Janus-CC is applied for pumpless transport of underwater gas bubbles even under harsh conditions. The movement of gas bubbles on the surface of the Janus-CC is interpreted based on the formed gaseous film on the aerophilic side of the Janus-CC. Various applications of the prepared Janus-CC for underwater bubble transportation, such as underwater gas distributor, gas collector membrane, gas transport for chemical reactions, unidirectional gas membrane, and elimination of gas bubbles in transport pipe, are presented.

TiO2 with Confined Water Boosts Ultrahigh Selective Enrichment of Phosphorylated Proteins

In the selective enrichment of phosphorylated proteins (PPs) from biological samples, the non-phosphorylated proteins (NPPs) adhered onto enrichment adsorbents due to the hydrophobic interaction, resulting in poor selectivity and low recovery of target PPs. Herein, superhydrophilic TiO₂-coated porous SiO₂ microspheres are prepared and boost remarkable selectivity toward standard PP spiked with 2000 mass-fold NPP interference. The outstanding performance of the superhydrophilic microspheres is attributed to the coordination interaction between TiO₂ and PPs, and the confined water layer generated from superhydrophilicity avoids the irreversible adsorption of NPPs by keeping NPP inner hydrophobic regions in a compact structure, which is verified by single molecule force spectroscopy, circular dichroism, and quartz crystal microbalance. This strategy for enrichment is expected to solve the challenge in proteomics and sheds light on the interactions between biomolecules and superwettability.

Smart Titanium Wire Used for the Evaluation of Hydrophobic/Hydrophilic Interaction by In-Tube Solid Phase Microextraction

Evaluation of the hydrophobic/hydrophilic interaction individually between the sorbent and target compounds in sample pretreatment is a big challenge. Herein, a smart titanium substrate with switchable surface wettability was fabricated and selected as the sorbent for the solution. The titanium wires and meshes were fabricated by simple hydrothermal etching and chemical modification so as to construct the superhydrophilic and superhydrophobic surfaces. The micro/nano hierarchical structures of the formed TiO₂ nanoparticles in situ on the surface of Ti substrates exhibited the switchable surface wettability. After UV irradiation for about 15.5 h, the superhydrophobic substrates became superhydrophilic. The morphologies and element composition of the wires were observed by SEM, EDS, and XRD, and their surface wettabilities were measured using the Ti mesh by contact angle goniometer. The pristine hydrophilic wire, the resulting superhydrophilic wire, superhydrophobic wire, and the UV-irradiated superhydrophilic wire were filled into a stainless tube as the sorbent instead of the sample loop of a six-port valve for on-line in-tube solid-phase microextraction. When employed in conjunction with HPLC, four kinds of wires were comparatively applied to extract six estrogens in water samples. The optimal conditions for the preconcentration and separation of target compounds were obtained with a sample volume of 60 mL, an injection rate of 2 mL/min, a desorption time of 2 min, and a mobile phase of acetonile/water (47/53, v/v). The results showed that both the superhydrophilic wire and UV-irradiated wire had the highest extraction efficiency for the polar compounds of estrogens with the enrichment factors in the range of 20-177, while the superhydrophobic wire exhibited the highest extraction efficiency for the non-polar compounds of five polycyclic aromatic hydrocarbons (PAHs). They demonstrated that extraction efficiency was mainly dependent on the surface wettability of the sorbent and the polarity of the target compounds, which was in accordance with the molecular theory of like dissolves like.

On-Demand Wettability via Combining fs Laser Surface Structuring and Thermal Post-Treatment

Laser surface texturing (LST) is one of the surface modification methods that increase or provide new abilities for the material surface. Textured surfaces could be applied in different industrial areas to reduce wear and friction, promote anti-fouling, improve osseointegration, and other similar uses. However, LST is still in development and for reaching industrial level further optimization is required. In this paper, different metal alloy surfaces were fabricated with several patterns using the same laser parameters on each material and the results were compared. This could lead to possible optimization on the industrial level. Furthermore, research on the wettability properties of material and texture patterns depending on heat treatment in different temperatures was performed, showing complete control for wettability (from hydrophilic to hydrophobic).

Anti-Biofouling Polymers with Special Surface Wettability for Biomedical Applications

The use of anti-biofouling polymers has widespread potential for counteracting marine, medical, and industrial biofouling. The anti-biofouling action is usually related to the degree of surface wettability. This review is focusing on anti-biofouling polymers with special surface wettability, and it will provide a new perspective to promote the development of anti-biofouling polymers for biomedical applications. Firstly, current anti-biofouling strategies are discussed followed by a comprehensive review of anti-biofouling polymers with specific types of surface wettability, including superhydrophilicity, hydrophilicity, and hydrophobicity. We then summarize the applications of anti-biofouling polymers with specific surface wettability in typical biomedical fields both in vivo and in vitro, such as cardiology, ophthalmology, and nephrology. Finally, the challenges and directions of the development of anti-biofouling polymers with special surface wettability are discussed. It is helpful for future researchers to choose suitable anti-biofouling polymers with special surface wettability for specific biomedical applications.

Inner Surface Hydrophilic Modification of PVDF Membrane with Tea Polyphenols/Silica Composite Coating

The use of Polyvinylidene fluoride (PVDF) membranes is constrained in wastewater treatment because of their hydrophobic nature. Therefore, a large number of researchers have been working on the hydrophilic modification of their surfaces. In this work, a superhydrophilic tea polyphenols/silica composite coating was developed by a one-step process. The composite coating can achieve not only superhydrophilic modification of the surface, but also the inner surface of the porous PVDF membrane, which endows the modified membrane with excellent water permeability. The modified membrane possesses ultrahigh water flux (15,353 L·m⁻²·h⁻¹). Besides this, the modified membrane can realize a highly efficient separation of oil/water emulsions (above 96%).

Multifunctional Laser-Induced Graphene Papers with Combined Defocusing and Grafting Processes for Patternable and Continuously Tunable Wettability from Superlyophilicity to Superlyophobicity

Functional surfaces with tunable and patternable wettability have attracted significant research interests because of remarkable advantages in biomedicine, environmental, and energy storage applications. Based on combined defocusing and grafting strategy for processing laser-induced graphene papers (LIGPs) with variable surface roughness (58.18-6.08 µm) and F content (0-25.9%), their wettability can be tuned continuously from superlyophilicity (contact angle CA ≈ 0^° ) to superlyophobicity (CA > 150^° ), for various liquids with a wide range of surface tensions from 27.5 to 72.8 mN m^-1 . In addition to reaching multiple wetting characteristics including amphiphilic, amphiphobic, and hydrophobic-oleophilic states, three designable processes are further developed for achieving LIGPs with various wetting patterns, including hydrophilic arrays or channels, hydrophobic-to-hydrophilic gradients, and Janus. Activated by the customly designed structures and properties, multifunctional and multi-scenario applications are successfully attempted, including 2D-/3D- directional cell cultivation, water transportation diode, self-triggered liquid transfer & collection, etc.

Single-Step Preparation of Ultrasmall Iron Oxide-Embedded Carbon Nanotubes on Carbon Cloth with Excellent Superhydrophilicity and Enhanced Supercapacitor Performance

Nanocomposites consisting of carbon materials and metal oxides are generally preferred as anodes in electrochemical energy storage. However, their low capacitance limits the achieved energy density of supercapacitors (SCs) in aqueous electrolytes. Herein, we propose a rapid combustion strategy to construct a novel electrode architecture-ultrasmall Fe₂O₃ anchoring on carbon nanotubes (FeO-CNT)-as a superhydrophilic and flexible anode for SCs. In 1 M Na₂SO₄ aqueous electrolyte, such an FeO-CNT-20 anode presents a high capacitance of 483.4 mF cm^-2 (326 F g^-1) at 1 mA cm^-2. The aqueous asymmetric supercapacitor devices (ASCs) assembled by FeO-CNT-20 and MnO₂ present a maximum operating potential of 2.0 V with a high areal energy density of 0.11 mWh cm^-2 at a power density of 0.5 mW cm^-2. The flexible solid-state ASCs display an energy density of 0.99 mWh cm^-3 at 14.3 mW cm^-3. The rapidly prepared FeO-CNT not only offers an attractive electrode for SCs but also would open up exciting new avenues to the rational design and large-scale preparation of Fe₂O₃-based nanocomposites for electrochemical energy storage.

Machine Learning Prediction of TiO2-Coating Wettability Tuned via UV Exposure

Surfaces with extreme wettability (too low, superhydrophobic; too high, superhydrophilic) have attracted considerable attention over the past two decades. Titanium dioxide (TiO₂) has been one of the most popular components for generating superhydrophobic/hydrophilic coatings. Combining TiO₂ with ethanol and a commercial fluoroacrylic copolymer dispersion, known as PMC, can produce coatings with water contact angles approaching 170°. Another property of interest for this specific TiO₂ formulation is its photocatalytic behavior, which causes the contact angle of water to be gradually reduced with rising timed exposure to UV light. While this formulation has been employed in many studies, there exists no quantitative guidance to determine or tune the contact angle (and thus wettability) with the composition of the coating and UV exposure time. In this article, machine learning models are employed to predict the required UV exposure time for any specified TiO₂/PMC coating composition to attain a certain wettability (UV-reduced contact angle). For that purpose, eight different coating compositions were applied to glass slides and exposed to UV light for different time intervals. The collected contact-angle data was supplied to different regression models to designate the best method to predict the required UV exposure time for a prespecified wettability. Two types of machine learning models were used: (1) parametric and (2) nonparametric. The results showed a nonlinear behavior between the coating formulation and its contact angle attained after timed UV exposure. Nonparametric methods showed high accuracy and stability with general regression neural network (GRNN) performing best with an accuracy of 0.971, 0.977, and 0.933 on the test, train, and unseen data set, respectively. The present study not only provides quantitative guidance for producing coatings of specified wettability, but also presents a generalized methodology that could be employed for other functional coatings in technological applications requiring precise fluid/surface interactions.

Modeling Bacterial Attachment Mechanisms on Superhydrophobic and Superhydrophilic Substrates

Superhydrophilic and superhydrophobic substrates are widely known to inhibit the attachment of a variety of motile and/or nonmotile bacteria. However, the thermodynamics of attachment are complex. Surface energy measurements alone do not address the complexities of colloidal (i.e., bacterial) dispersions but do affirm that polar (acid-base) interactions (ΔGAB) are often more significant than nonpolar (Lifshitz-van der Waals) interactions (ΔGLW). Classical DLVO theory alone also fails to address all colloidal interactions present in bacterial dispersions such as ΔGAB and Born repulsion (ΔGBorn) yet accounts for the significant electrostatic double layer repulsion (ΔGEL). We purpose to model both motile (e.g., P. aeruginosa and E. coli) and nonmotile (e.g., S. aureus and S. epidermidis) bacterial attachment to both superhydrophilic and superhydrophobic substrates via surface energies and extended DLVO theory corrected for bacterial geometries. We used extended DLVO theory and surface energy analyses to characterize the following Gibbs interaction energies for the bacteria with superhydrophobic and superhydrophilic substrates: ΔGLW, ΔGAB, ΔGEL, and ΔGBorn. The combination of the aforementioned interactions yields the total Gibbs interaction energy (ΔGtot) of each bacterium with each substrate. Analysis of the interaction energies with respect to the distance of approach yielded an equilibrium distance (deq) that seems to be independent of both bacterial species and substrate. Utilizing both deq and Gibbs interaction energies, substrates could be designed to inhibit bacterial attachment.

Superwetting Bi2MoO6/Cu3(PO4)2 Nanosheet-Coated Copper Mesh with Superior Anti-Oil-Fouling and Photo-Fenton-like Catalytic Properties for Effective Oil-in-Water Emulsion Separation

Superwetting materials with excellent anti-oil-fouling performance for the treatment of oily wastewater are urgently demanded in practice. In this work, aiming at effectively separating diverse oil-in-water emulsions, a multifunctional Bi₂MoO₆/Cu₃(PO₄)₂ nanosheet-coated copper mesh was successfully fabricated by the combination of chemical oxidation and ultrasonic irradiation deposition methods. The resultant copper mesh exhibited superior superhydrophilicity/underwater superoleophobicity and, more importantly, preferable anti-oil-fouling property benefitting from the stable and firm hydration layer. A series of oil/water separation experiments for the highly emulsified surfactant-free and surfactant-stabilized oil-in-water emulsions were conducted, with the respective permeation fluxes of up to 3000 and 700 L·m^-2·h^-1 and the corresponding separation efficiencies of 99.5 and 98.6% solely driven by gravity. Meanwhile, considering the photo-Fenton-like catalytic activity of Bi₂MoO₆, the as-fabricated copper mesh exhibited excellent degradation ability toward organic pollutants under visible light irradiation. More importantly, stability tests were performed to evaluate the ability to cope with the harsh environments for practical applications. With the outstanding performances of high separation efficiency, desirable photo-Fenton-like catalytic capacity, and strong stability, the Bi₂MoO₆/Cu₃(PO₄)₂ nanosheet-coated copper mesh holds promising potential for purifying emulsified wastewater.

Explosive Pancake Bouncing on Hot Superhydrophilic Surfaces

The rapid detachment of liquid droplets from engineered surfaces in the form of complete rebound, pancake bouncing, or trampolining has been extensively studied over the past decade and is of practical importance in many industrial processes such as self-cleaning, anti-icing, energy conversion, and so on. The spontaneous trampolining of droplets needs an additional low-pressure environment and the manifestation of pancake bouncing on superhydrophobic surfaces requires meticulous control of macrotextures and impacting velocity. In this work, we report that the rapid pancake-like levitation of impinging droplets can be achieved on superhydrophilic surfaces through the application of heating. In particular, we discovered explosive pancake bouncing on hot superhydrophilic surfaces made of hierarchically non-interconnected honeycombs, which is in striking contrast to the partial levitation of droplets on the surface consisting of interconnected microposts. This enhanced droplet bouncing phenomenon, characterized by a significant reduction in contact time and increase in the bouncing height, is ascribed to the production and spatial confinement of pressurized vapor in non-interconnected structures. The manifestation of pancake bouncing on the superhydrophilic surface rendered by a bottom-to-up boiling process may find promising applications such as the removal of trapped solid particles.

Superhydrophilic Ni-based Multicomponent Nanorod-Confined-Nanoflake Array Electrode Achieves Waste-Battery-Driven Hydrogen Evolution and Hydrazine Oxidation

The low thermodynamic potential (-0.33 V) and safe by-product of N₂ /H₂ O, make utilizing hydrazine oxidation reaction (HzOR) to replace thermodynamically-unfavorable and kinetically-sluggish oxygen evolution reaction a promising tactic for energy-efficient hydrogen production. However, the complexity of bifunctionality increases difficulties for effective material design, thus hindering the large-scale hydrogen generation. Herein, we present the rationally designed synthesis of superhydrophilic Ni-based multicomponent arrays (Ni NCNAs) composed of 1D nanorod-confined-nanoflakes (2D), which only needs -26 mV of working potential and 47 mV of overpotential to reach 10 mA cm^-2 for HzOR and HER, respectively. Impressively, this Ni NCNA electrode exhibits the top-level bifunctional activity for overall hydrazine splitting (OHzS) with an ultralow voltage of 23 mV at 10 mA cm^-2 and a record-high current density of 892 mA cm^-2 at just 0.485 V, also achieves the high-speed hydrogen yield driven by a waste AAA battery for OHzS.

Simply Adjusting the Unidirectional Liquid Transport of Scalable Janus Membranes toward Moisture-Wicking Fabric, Rapid Demulsification, and Fast Oil/Water Separation

Inspired by nature, Janus membranes with unidirectional liquid transport (ULT) were developed to be used in the fields of fog collection, moisture-wicking fabrics, demulsification, etc. However, the obtained Janus membranes are often unifunctional, and it is still a great challenge to adjust the ULT of Janus membranes for multifunctional applications. Herein, a scalable, low-cost, and machine-washable Janus membrane was developed by combining the cyclic self-assembly of phytic acid and Fe^III and a one-side spraying coating of poly(dimethylsiloxane) (PDMS), featuring adjustable ULT upon challenge for multifunctional applications. By controlling the amount of PDMS, the Janus membranes exhibit two different performances, ULT and switchable permeation. The prepared Janus membranes achieved an excellent moisture-wicking fabric (1.6× the water evaporation rate of cotton), fast water collection under oil, rapid demulsification, and the efficient separation of an oil/water mixture. The separation efficiency of a light or heavy oil from water was higher than 99.9% even after 10 separation cycles, and the flux of the separation was up to 2.55 × 10⁴ or 2.38 × 10⁴ L m^-2 h^-1, respectively. This study could provide an idea for the development of more Janus membranes with adjustable performances to realize multifunctional applications.

Simple Amphoteric Charge Strategy to Reinforce Superhydrophilic Polyvinylidene Fluoride Membrane for Highly Efficient Separation of Various Surfactant-Stabilized Oil-in-Water Emulsions

Long-term efficient separation of highly emulsified oily wastewater is challenging. Reported herein is the preparation of a reinforced superhydrophilic, underwater superoleophobic membrane with demulsification properties using active iron nanoparticles in situ generated on a polydopamine (PDA)/polyethylenimine (PEI)-modified polyvinylidene fluoride (PVDF) membrane surface. A stable zwitterionic structure is fabricated on the membrane surface and provides it with an excellent capability of binding a hydration layer, leading to enhanced superhydrophilic/underwater superoleophobic properties. The interaction between the membrane surface and water is quantified using the relaxation time of water. After iron nanoparticles in situ anchoring, the superhydrophilic, underwater superoleophobic PDA/PEI modified PVDF membrane shows more stable flux behaviors, higher oil separation efficiency, demulsification, and excellent antioil-fouling properties for various anionic, nonionic, and cationic surfactant-stabilized oil-in-water emulsions in a crossflow filtration system. The reinforced hydration layer and the amphoteric charged demusification properties of the membrane play important roles in enhancing the membrane separation performance. The reinforced membrane also exhibits excellent cleaning and reusability performance in long-term operations. The outstanding separation performance, as well as the simple and cost-effective fabrication process of the membrane with various favorable properties, highlight its promise in practical emulsified oily water applications.

Superhydrophilic Coating with Antibacterial and Oil-Repellent Properties via NaIO4-Triggered Polydopamine/Sulfobetaine Methacrylate Polymerization

Superhydrophilic coatings have been widely used for the surface modification of membranes or biomedical devices owing to their excellent antifouling properties. However, simplifying the modification processes of such materials remains challenging. In this study, we developed a simple and rapid one-step co-deposition process using an oxidant trigger to fabricate superhydrophilic surfaces based on dopamine chemistry with sulfobetaine methacrylate (SBMA). We studied the effect of different oxidants and SBMA concentrations on surface modification in detail using UV-VIS spectrophotometry, dynamic light scattering, atomic force microscopy, X-ray photoelectron spectroscopy, and surface plasmon resonance. We found that NaIO4 could trigger the rate of polymerization and the optimum ratio of dopamine to SBMA is 1:25 by weight. This makes the surface superhydrophilic (water contact angle < 10°) and antifouling. The superhydrophilic coating, when introduced to polyester membranes, showed great potential for oil/water separation. Our study provides a complete description of the simple and fast preparation of superhydrophilic coatings for surface modification based on mussel-inspired chemistry.

High-Efficiency Boiling Heat Transfer Interfaces Composed of Electroplated Copper Nanocone Cores and Low-Thermal-Conductivity Nickel Nanocone Coverings

We demonstrate that copper-based super-thin high-efficiency boiling heat transfer (BHT) interfaces can be obtained via electroplating hierarchical nickel nanocone coverings on the surface of copper nanocone cores. By regulating surface morphologies, wettability, and mass and heat transfer properties of hierarchical structures, we reveal the regulation rules of their performance. Based on this, we obtain the optimized BHT interfaces with a thickness of only 6.4 μm, which shows 228% enhancement in the maximal heat transfer coefficient, 71% enhancement in the critical heat flux, and 68% decrease in the superheat for the onset of nucleate boiling, as compared to the flat copper surface. Our studies clearly indicate that, although the in situ growth of nickel nanocones can unavoidably increase the interface thermal resistance of hierarchical structures, its optimization can still enhance BHT performance. This may be ascribed to the coupling of several interface effects such as more heat transfer area, more nucleation sites, smaller bubble departure sizes, and stronger liquid supply ability caused by hierarchical structures. Our work opens up a new avenue for the development of copper-based super-thin high-efficiency BHT interfaces, which would help enhance the efficiency of energy utilization and heat dissipation of various thermal devices.

The preparation and characterization of uniform nanoporous structure on glass

A novel fabrication method of uniform porous structures on the glass surface is proposed. The hydrofluoric acid fog formed by air-jet atomization etches the glass surface to fabricate nanoporous structure (NPS) on glass surface. This NPS shows the enhanced average light transmittance of approximately 92.9% and the superhydrophilic property with a contact angle less than 1° which presents an excellent anti-fog property. Passivated by fluorosilane, the NPS shows nearly the superhydrophobic property with a contact angle of 141.2°. This fabrication method has shown promising application prospects due to its simplicity, low cost and efficiency, which can be easily applied to large-scale industrial production.

Micro/Nanoscale Structured Superhydrophilic and Underwater Superoleophobic Hybrid-Coated Mesh for High-Efficiency Oil/Water Separation

A novel micro/nanoscale rough structured superhydrophilic hybrid-coated mesh that shows underwater superoleophobic behavior is fabricated by spray casting or dipping nanoparticle–polymer suspensions on stainless steel mesh substrates. Water droplets can spread over the mesh completely; meanwhile, oil droplets can roll off the mesh at low tilt angles without any penetration. Besides overcoming the oil-fouling problem of many superhydrophilic coatings, this superhydrophilic and underwater superoleophobic mesh can be used to separate oil and water. The simple method used here to prepare the organic–inorganic hybrid coatings successfully produced controllable micro-nano binary roughness and also achieved a rough topography of micro-nano binary structure by controlling the content of inorganic particles. The mechanism of oil–water separation by the superhydrophilic and superoleophobic membrane is rationalized by considering capillary mechanics. Tetraethyl orathosilicate (TEOS) as a base was used to prepare the nano-SiO₂ solution as a nano-dopant through a sol-gel process, while polyvinyl alcohol (PVA) was used as the film binder and glutaraldehyde as the cross-linking agent; the mixture was dip-coated on the surface of 300-mesh stainless steel mesh to form superhydrophilic and underwater superoleophobic film. Properties of nano-SiO₂ represented by infrared spectroscopy and surface topography of the film observed under scanning electron microscope (SEM) indicated that the film surface had a coarse micro–nano binary structure; the effect of nano-SiO₂ doping amount on the film’s surface topography and the effect of such surface topography on hydrophilicity of the film were studied; contact angle of water on such surface was tested as 0° by the surface contact angle tester and spread quickly; the underwater contact angle to oil was 158°, showing superhydrophilic and underwater superoleophobic properties. The effect of the dosing amount of cross-linking agent to the waterproof swelling property and the permeate flux of the film were studied; the oil–water separation effect of the film to oil–water suspension and oil–water emulsion was studied too, and in both cases the separation efficiency reached 99%, which finally reduced the oil content to be lower than 50 mg/L. The effect of filtration times to permeate flux was studied, and it was found that the more hydrophilic the film was, the stronger the stain resistance would be, and the permeate flux would gradually decrease along with the increase of filtration times.

Nanoscale and Macroscale Effects of Mineral Deposition During Water Evaporation on Nanoporous Surfaces

Recent studies have indicated that droplet evaporation heat transfer can be substantially enhanced by fabricating a thin nanoporous superhydrophilic layer on a metal substrate. Such surfaces have immense potential to improve spray cooling processes, however, little durability testing of the surface has been performed. In spray cooling applications, as water evaporates any impurities in the water will be deposited onto the surface. Primarily, this investigation serves to demonstrate how minerals in hard water deposit on the surface and interact with the ZnO nanopillars of the superhydrophilic surface. Quantifying the effects of mineral scale on droplet spreading and vaporization heat transfer on the surface is important in determining implementation requirements to advance the surface into industry applications. Micrographs of the surface demonstrate minerals deposit nonuniformly and quickly fill the nanostructure. Despite a reduction in the extent of droplet spreading due to the mineral deposition, scaled surfaces still demonstrated improved thermal performance compared to an uncoated, smooth copper surface. Scale tended to build up on previously deposited scale, leaving largely uncoated areas where droplets chose to preferentially spread and resulting in a continued low contact angle. Maintaining these uncoated areas and reducing the contaminants present in the water will extend the life and performance of the nanostructured surface.

Unlocking the Potential of Organ-on-Chip Models through Pumpless and Tubeless Microfluidics

Microfluidic organs-on-chips are rapidly being developed toward eliminating the shortcomings of static in vitro models and better addressing basic and translational research questions. A critical aspect is the dynamic culture environment they provide. However, the associated inherent requirement for controlled fluid shear stress (FSS) and therefore the need for precise pumps limits their implementation. To address this issue, here a novel approach to manufacture pumpless and tubeless organs-on-chips is reported. It relies on the use of a hydrophilic thread to provide a driving force for the perfusion of the cell culture medium through constant evaporation in the controlled conditions of a cell incubator. Well-defined and tuneable flow rates can be applied by adjusting the length and/or diameter of the thread. This approach for the preparation of an intestine-on-chip model based on the Caco-2 cell line is validated. Five days culture under 0.02 dyn·cm^-2 shear conditions yield monolayers similar to those prepared using a high-precision peristaltic pump. A pumpless device can also be used to delineate the effect of FSS on the phenotype of adenocarcinomic human alveolar basal epithelial A549 cells. It is anticipated that the pumpless approach will facilitate and herefore increase the use of organs-on-chips models in the future.

Wettability-Engineered Meshes for Gas Microvolume Precision Handling in Liquids

The interaction of rising gas bubbles with submerged air-repelling or air-attracting surfaces is relevant to various technological applications that rely on gas-microvolume handling or removal. This work demonstrates how submerged metal meshes with super air-attracting/repelling properties can be employed to manipulate microvolumes of air, rising buoyantly in the form of bubbles in water. Superaerophobic meshes are observed to selectively allow the passage of air bubbles depending on the mesh pore size, the bubble volume-equivalent diameter, and the bubble impact velocity on the mesh. On the other hand, superaerophilic meshes reduce or amplify the volume captured from a train of incoming bubbles. Finally, a spatial wettability pattern on the mesh is used to control the size of the outgoing bubble, and an empirical relation is formulated to predict the released gas volume. The study demonstrates how porous materials with controlled wettability can be used to precisely modulate and control the outcome of bubble/mesh interactions.

High-Performance Salt-Rejecting and Cost-Effective Superhydrophilic Porous Monolithic Polymer Foam for Solar Steam Generation

Direct solar desalination with excellent solar photothermal efficiency, lower cost, and extended generator device lifetime is beneficial to increase potable water supplies. To address fundamental challenges in direct solar desalination, herein, we present a new and facile method for the scalable fabrication of the polymer porous foam (VMP) as salt-resistant photothermal materials, which was synthesized through a one-step hydrothermal method using styrene and 1-vinyl-3-ethylimidazolium tetrafluoroborate as monomers and N,N'-methylenebisacrylamide as the cross-linking agent. The as-resulted VMP shows excellent mechanical properties which could have a compression strain of 30%, resulting in its superior processability for practical operation. In addition, by taking advantage of its inherent low density, well-controlled porous structure (porosity is 73.81%), and extremely low thermal conductivity (0.03204 W m^-1 K^-1), the VMP exhibits an excellent solar evaporation property, and the solar photothermal efficiency can reach more than 88% under 1 kW m^-2 irradiation. Moreover, the introduction of ionic liquid moiety (imidazolium tetrafluoroborate) into VMP results in its interesting superhydrophilic wettability, which can accelerate water transportation (wetting in 5s) and resolve the crystalline salt within 1.13 h. In addition, the interconnected macropores of the VMP, as water channels, can replenish the vaporized brine on the surface to prevent salt from adhering. The VMP shows a salt-resistant performance, for example, its solar evaporation efficiency remains nearly unchanged after 6 h duration under 1 sun irradiation. Based on its simple and cost-effective manufacturing process, excellent solar photothermal efficiency, and salt resistance, our VMP may be a promising candidate as photothermal materials for practical desalination from seawater and other wastewater.

Rapid and Scalable Wire-bar Strategy for Coating of TiO2 Thin-films: Effect of Post-Annealing Temperatures on Structures and Catalytic Dye-Degradation

Titanium dioxide (TiO2) thin films were rapidly coated on Corning glass substrates from the precursor solution using the wire-bar technique at the room temperature and then post-annealed at 400, 500 and 600 °C for 1 h under atmospheric conditions. The structural, morphological, optical, wettability and photocatalytic properties of the films were studied. X-ray diffraction analysis confirmed the formation of an anatase TiO2 structure irrespective of the post-annealing temperatures. The optical transparency of the films in the visible range was measured to be > 70%. A water contact angle (WCA) of ~0° was observed for TiO2 thin-film, post-annealed at 400 °C and 500 °C. However, WCA of 40.3° was observed for post-annealed at 600 °C. The photocatalytic dye-degradation using post-annealed thin-film was investigated indicating a steady improvement in the dye-degradation percentage (from 24.3 to 29.4%) with the increase of post-annealing temperature. The demonstrated TiO2 thin-films deposited by wire-bar coating technique showed promises for the manufacturing of large-area cost-effective self-cleaning window glass.

Ultrascalable Three-Tier Hierarchical Nanoengineered Surfaces for Optimized Boiling

Nanostructure-enhanced pool and flow boiling has the potential to increase the efficiency of a plethora of applications. Past studies have developed well-ordered, nonscalable structures to study the fundamental limitations of boiling such as bubble nucleation, growth, and departure, often in a serial manner without global optimization. Here, we develop a highly scalable, conformal, cost-effective, rapid, and tunable three-tier hierarchical surface deposition technique capable of holistically creating micropores, microscale dendritic clusters, and nanoparticles on arbitrary surfaces. We use this technique to investigate the pool boiling heat transfer performance with focus on the bubble departure diameter and frequency. By tuning the structure length scale, the pool boiling characteristics were optimized through a multipronged approach, including increasing nucleation site density (micropores), regulating bubble evolution behavior (dendritic structures), improving surface wickability (nanoscale particles and channels), and separating liquid and vapor pathways (micropores and micro/nanochannels). Ultrahigh critical heat fluxes (CHF) ≈400 W/cm² were obtained, corresponding to an enhancement of ≈245% compared to smooth copper surfaces. To study in situ bubble departure and coalescence dynamics, we developed and used high-magnification in-liquid endoscopy. Our work reveals the existence of a linear relationship between the bubble departure diameter/frequency near the onset of nucleate boiling and CHF enhancement. Our study not only develops a highly scalable, conformal, and rapid micro/nanostructuring technique, it outlines design guidelines for the holistic optimization of boiling heat transfer for energy and water applications.

Superhydrophilic, Underwater Superoleophobic, and Highly Stretchable Humidity and Chemical Vapor Sensors for Human Breath Detection

Humidity and chemical vapor sensors have promising applications in the field of environment protection, human healthcare, and so forth. It is still challenging to develop sensor materials that can serve as both humidity and chemical vapor sensors with high sensitivity, low detection limit, and excellent stretchability, repeatability, and reliability. In this study, a flexible, stretchable, and conductive nanofiber composite (CNC) with superhydrophilicity and underwater superoleophobicity is prepared by acidified carbon nanotube (ACNT) decoration onto the thermoplastic polyurethane (PU) nanofiber surface. ACNT introduction increases both the Young's modulus and tensile strength and almost maintains the superelasticity of the PU nanofibrous membrane. The as-obtained CNC could be used to detect both moisture and chemical vapors. When used as the humidity sensor, ACNTs can absorb surrounding water molecules and thus increase their resistance. On the other hand, the PU can be swollen by different chemical vapors, which can, to a different extent, damage the conductive network inside the composite and cause the increase of the composite resistance. The CNC can be integrated with a mask for real-time detection of human respiration. The CNC-based chemical vapor sensor possesses low detection limit, quick response, good selectivity, and excellent recyclability (even in a high humid environment) and has potential applications in monitoring biomarker gases from human breath.

Study of Oil Dewetting Ability of Superhydrophilic and Underwater Superoleophobic Surfaces from Air to Water for High-Effective Self-Cleaning Surface Designing

The superhydrophilic self-cleaning surface can perfectly deal with oil pollution, which cannot be realized by the superhydrophobic surface. This research is designed to study the mechanism of wetting behavior of superhydrophilic coating with different function groups and guide to design a stable self-cleaning surface. We prepare several hydrophilic coatings including nonionic, ionic, and zwitterionic coatings to investigate their self-cleaning performance underwater when they have been polluted by oil in the dry state. The chemical composition, surface roughness, static and dynamic wettability, underwater oil adhesive force, and swelling degree of the coatings are studied to explore their oil dewetting mechanism. The results indicate that the wettability of the coating to water and oil is the key factor to determine the self-cleaning performance. The smooth 3-sulfopropyl methacrylate potassium salt (SA) anionic coating shows the best self-cleaning performance even when polluted by heavy crude oil in the dry state in air. It is also found that in the dry state, the rough hydrophilic anionic surface will lock up the oil in the structures and then lose its self-cleaning ability underwater, whereas the oil droplet can detach from the smooth coating surface quickly. Meanwhile, the superhydrophilic and underwater superoleophobic SA anionic surfaces also exhibit excellent anti-fogging and oil-water separation performance.

Superwetting Polymeric Three Dimensional (3D) Porous Materials for Oil/Water Separation: A Review

Oil spills and the emission of oily wastewater have triggered serious water pollution and environment problems. Effectively separating oil and water is a world-wide challenge and extensive efforts have been made to solve this issue. Interfacial super-wetting separation materials e.g., sponge, foams, and aerogels with high porosity tunable pore structures, are regarded as effective media to selectively remove oil and water. This review article reports the latest progress of polymeric three dimensional porous materials (3D-PMs) with super wettability to separate oil/water mixtures. The theories on developing super-wetting porous surfaces and the effects of wettability on oil/water separation have been discussed. The typical 3D porous structures (e.g., sponge, foam, and aerogel), commonly used polymers, and the most reported techniques involved in developing desired porous networks have been reviewed. The performances of 3D-PMs such as oil/water separation efficiency, elasticity, and mechanical stability are discussed. Additionally, the current challenges in the fabrication and long-term operation of super-wetting 3D-PMs in oil/water separation have also been introduced.

Synthesis of Negatively Charged Polyol-Functional PSF Membranes with Good Hydrophilic and Efficient Boron Removal Properties

Boron removal remains a major barrier to water purification, it is important to develop a specialized adsorption membrane for boron removal. By means of a simple and effective method, a hydrophilic membrane for boron removal with a polyhydroxy functional group on the surface was prepared. Firstly, a polysulfone (PSF) membrane was modified by co-depositing polyethyleneimine (PEI) with dopamine (DA) in one-step to produce amine-rich surfaces, then the DA/PEI-functionalized membranes were reacted with glycidol, with the prepared membranes corresponding to PSF-PDA/PEI membranes and PSF-diol membranes. The prepared membranes were characterized by water-uptake, FTIR, (X-ray photoelectron spectroscopy) XPS, (Field emission scanning electron microscope) FESEM, and zeta potential measurements. The hydrophilicity of the membrane was characterized by the static water contact angle (WCA) test. In addition, we systematically studied the impact of initial boron concentration, chelating time, and pH value on boron removal performance. The results showed that the PSF-diol membrane had strong hydrophilicity with a WCA of about 38°. The maximum adsorption capacity of boron appeared to be 1.61 mmol/g within 10 min at a boron concentration of 300 mg/L. Adsorption kinetics showed that saturation adsorption can be achieved in minutes at the initial concentration of 5 mg/L, which is beneficial to a rapid filtration process.

3D Printing of an Oil/Water Mixture Separator with In Situ Demulsification and Separation

Currently, many meshes, membranes, and fabrics with extreme wettability of superhydrophobicity/superoleophilicity, or superhydrophilicity and underwater superoleophobicity are promising candidates for oil/water mixture separation. Nevertheless, a facile yet effective way to design and fabricate porous mesh still remains challenging. In this work, fused deposition modeling (FDM) 3D printing of Fe/polylactic acid (PLA) composites was employed to fabricate superhydrophilic and underwater superoleophobic mesh (S-USM) with hydrogel coatings via the surface polymerization of Fe(II)-mediated redox reaction. In addition, salt of aluminum chloride was incorporated within the hydrogel coating, which was attributed to strengthening the demulsification of oil-in-water emulsions, resulting in efficient separation of oil-in-water mixtures. The S-USM was efficient for a wide range of oil-in-water mixtures, such as dodecane, diesel, vegetable oil, and even crude oil, with a separation efficiency of up to 85%. In this study, the flexible design and fabrication of 3D printing were used for the facile creation of spherical oil skimmers with hydrogel coatings that were capable of removing the floating oil. Most importantly, this work is expected to promote post-treatment processes using 3D printing as a new manufacturing technology and, in this way, a series of devices of specific shape and function will be expanded to satisfy desired requirements and bring great convenience to personal life.

Swelling Poly(ionic liquid) Supported by Three-Dimensional Wire Mesh for Oil/Water Separation

A kind of oil/water separation membrane, combining poly(ionic liquid) (PIL) and three-dimensional (3D) wire mesh, was designed and prepared via one-step photopolymerization of an ionic liquid monomer 1,8-triethylene glycoldiyl-3,3'-divinylimidazolium dibromide ([DVIm-(EG)₃]Br₂) with acrylic acid in the mesh. The composite membrane (PIL@Mesh) had the advantages of anti-oil-adhesion property and high mechanical strength simultaneously. The morphology of PIL@Mesh characterized by scanning electron microscopy (SEM) and Cryo-SEM demonstrated that PIL swelled in water to construct microscale 3D networks. The 3D networks of swelling PIL were capable of forming a hydration layer and endowed PIL@Mesh with superhydrophilicity, which made the membrane to transport water but to intercept oil. PIL@Mesh showed excellent separation efficiency (above 99.9%) for various oil/water mixtures, large water flux (47 L·m^-2·s^-1), and high intrusion pressure (1.2 kPa). Meanwhile, it performed well in recyclability and corrosion-resistant under harsh conditions, such as acid, alkaline, and salty environments.

One-Step Synthesis of Environmentally Friendly Superhydrophilic and Superhydrophobic Sponges for Oil/Water Separation

Environmentally friendly superhydrophilic and superhydrophobic sponges were synthesized using a one-step approach for oil/water separation. A superhydrophilic or superhydrophobic sponge (MFS/CC-DKGM or MFS/CC-PDMS) was synthesized by one-step coating of melamine formaldehyde sponge (MFS) with a mixture of calcium carbonate (CC) rods and deacetylized Konjac glucomannan (DKGM) [or polydimethylsiloxane (PDMS)]. The MFS/CC-PDMS showed excellent absorption capacity, which reached 52–76 g/g following immersion into various types of oil/water mixtures. Furthermore, the MFS/CC-DKGM and MFS/CC-PDMS exhibited excellent water- and oil-flux performances, which reached 4,702 L/m² h and 19,591 L/m² h, respectively, when they were used as filters. The MFS/CC-DKGM and MFS/CC-PDMS maintained their wettability characteristics relatively well after the chemical, thermal, and mechanical stability tests.

Ultrastable Underwater Anti-Oil Fouling Coatings from Spray Assemblies of Polyelectrolyte Grafted Silica Nanochains

Surfaces that have superhydrophilic characteristics are known to exhibit extreme oil repellency under water, which is attractive for applications including anti-fogging, water-oil separations, and self-cleaning. However, superhydrophilic surfaces can also be easily fouled and lose their extreme oil repellency, which limits their usage in practical applications. In this work, we create an anti-oil fouling coating by spray coating poly(acrylic acid) (PAA)-grafted SiO₂ nanochains (approximately 45 nm wide and 300 nm long) onto solid surfaces, forming a nanoporous film exhibiting superhydrophilicity (water contact angle in air ≈ 0°) and underwater superoleophobicity (dichloroethane contact angle ≥ 165°). The polymer-grafted nanochain assemblies exhibit extremely low contact angle hysteresis (<1°) and small adhesion hysteresis (-0.05 mN m^-1), and thus, oil can readily roll off from the surface when the coating is immersed in water. Compared to other superhydrophilic surfaces, we show that both the unique structure of spray-assembled nanochains and the hygroscopic nature of PAA are essential to enable ultrastable anti-oil fouling. Even after the PAA-grafted nanochain coating is purposely fouled by oil, oil can be readily and completely expelled and lifted-off from the coating within 10 s when placed under water. Further, we show that our coating retains underwater superoleophobicity even after being subjected to shearing under water for more than 168 h. Our approach offers a simple yet versatile method to create an ultrastable superhydrophilic and anti-oil fouling coating via a scalable manufacturing method.

Novel reversibly switchable wettability of superhydrophobic-superhydrophilic surfaces induced by charge injection and heating

Reversibly switching wettability between superhydrophobicity and superhydrophilicity has attracted widespread interest because of its important applications. In this work, we propose a reversible superhydrophobic-superhydrophilic conversion induced by charge injection and heating. Different from the conventional electrowetting phenomenon caused by the accumulation of solid-liquid interfacial charges, we discovered a phenomenon where charge injection and accumulation at the solid surface results in a sharp increase in wettability. The wettability of a sprayed SiO₂ nanoparticle coating on a glass slide was shown to change from superhydrophobic to superhydrophilic by charge injection and heating, and the superhydrophobicity was restored by heating, verifying a reversible superhydrophobic-superhydrophilic conversion. The influence of voltage, temperature, and time on the coating wettability and its durability under reversible conversion have been studied.

Continuous Directional Water Delivery on the 3D-Printed Arrowhead Microstructure Array

Unidirectional transport is attracting increasing attention in the field of microfluidics, because it does not require an external energy supply. However, most of the current self-driving structures are still plagued with persistent problems that restrict their practical applications. These include low transport velocity, short transport distance, and complex structure. This work reports the design of a new arrowhead microstructure array, on which liquid transport can reach speeds of 23 mm/s and the ratio of transport length to channel width (L/R) can reach up to approximately 40. This structure drives liquid through a unique arrow conformation, which can induce capillary force and arrest the reverse motion of the liquid simultaneously. By means of theory, simulation, and experiment, we have studied the mechanism of liquid transport on this structure. We provide a detailed discussion of the relationship between the velocity of liquid transport and the microstructural dimensions. The findings may inspire the design of novel, unidirectional, liquid-spreading surfaces.

Self-Cleaning: From Bio-Inspired Surface Modification to MEMS/Microfluidics System Integration

This review focuses on self-cleaning surfaces, from passive bio-inspired surface modification including superhydrophobic, superomniphobic, and superhydrophilic surfaces, to active micro-electro-mechanical systems (MEMS) and digital microfluidic systems. We describe models and designs for nature-inspired self-cleaning schemes as well as novel engineering approaches, and we discuss examples of how MEMS/microfluidic systems integrate with functional surfaces to dislodge dust or undesired liquid residues. Meanwhile, we also examine "waterless" surface cleaning systems including electrodynamic screens and gecko seta-inspired tapes. The paper summarizes the state of the art in self-cleaning surfaces, introduces available cleaning mechanisms, describes established fabrication processes and provides practical application examples.

Nanostructured and oriented metal-organic framework films enabling extreme surface wetting properties

We report on the synthesis of highly oriented and nanostructured metal-organic framework (MOF) films featuring extreme surface wetting properties. The Ni- and Co- derivatives of the metal-catecholate series (M-CAT-1) were synthesized as highly crystalline bulk materials and thin films. Oriented pillar-like nanostructured M-CAT-1 films exhibiting pronounced needle-like morphology on gold substrates were established by incorporating a crystallization promoter into the film synthesis. These nanostructured M-CAT-1 MOF films feature extreme wetting phenomena, specifically superhydrophilic and underwater superoleophobic properties with water and underwater oil-contact angles of 0° and up to 174°, respectively. The self-cleaning capability of the nanostructured, needle-like M-CAT-1 films was illustrated by measuring time-dependent oil droplet rolling-off a tilted surface. The deposition of the nanostructured Ni-CAT-1 film on a large glass substrate allowed for the realization of an efficient, transparent, antifog coating, enabling a clear view even at extreme temperature gaps up to ≈120 °C. This work illustrates the strong link between MOF film morphology and surface properties based on these framework materials.

Creation of Superhydrophobic and Superhydrophilic Surfaces on ABS Employing a Nanosecond Laser

A nanosecond green laser was employed to obtain both superhydrophobic and superhydrophilic surfaces on a white commercial acrylonitrile-butadiene-styrene copolymer (ABS). These wetting behaviors were directly related to a laser-induced superficial modification. A predefined pattern was not produced by the laser, rather, the entire surface was covered with laser pulses at 1200 DPI by placing the sample at different positions along the focal axis. The changes were related to the laser fluence used in each case. The highest fluence, on the focal position, induced a drastic heating of the material surface, and this enabled the melted material to flow, thus leading to an almost flat superhydrophilic surface. By contrast, the use of a lower fluence by placing the sample 0.8 µm out of the focal position led to a poor material flow and a fast cooling that froze in a rugged superhydrophobic surface. Contact angles higher than 150° and roll angles of less than 10° were obtained. These wetting behaviors were stable over time.

Facile Fabrication of Multi-Structured SiO₂@PVDF-HFP Nanofibrous Membranes for Enhanced Copper Ions Adsorption

The low-cost, heavy metal ion (Cu(II)) adsorptive multi-structured nanofibrous membranes of silicon oxide naonoparticles in-situ anchored polyvinylidene fluoride-hexafluoropropylene (SiO₂@PVDF-HFP) fibers were fabricated by the facile electrospinning technique combined with sol⁻gel strategy. To explore the benefits of the structure-related Cu(II) adsorption capacity, the fiber diameters of SiO₂@PVDF-HFP nanofibrous membranes were changed which also resulted in the change of their porosity. Taking advantage of the constructed multi-structures and efficient fiber morphology regulation which not only changed the PVDF-HFP nanofibrous membrane from hydrophobic to superhydrophilic but also increased the porosity of the membrane, the SiO₂@PVDF-HFP nanofibrous membrane with a smaller diameter and a larger porosity exhibits higher Cu(II) adsorption capacity. The adsorption amount was approximate to 21.9 mg per gram of the membrane, which was higher than that of membranes with larger fiber diameter (smaller porosity) and the smooth one. Furthermore, the model isotherms of Freundlich and Langmuir, as well as the kinetic models of pseudo-first-order and pseudo-second-order were preferred to analyze the adsorption equilibrium data. The Freundlich model and the pseudo-first-order were well fitted to the adsorption experimental data. It not only uncovers the structure-related-property of multi-structured nanofibrous membranes, but also provides an efficient and facile way to design heavy metal ion adsorption materials.