Special Wettability Research Articles

Dual-responsive shape memory polymer arrays with smart and precise multiple-wetting controllability

Smart-controlled surface wettability from superhydrophilicity to superhydrophobicity has been extensively explored, and stimulus-responsive strategies have been widely accepted as a useful method to realize reversibility. However, achieving smart and precise wetting control remains challenging because most previous studies focused on stimulating single surface chemistry or microstructures. Herein, a dual-stimulus-responsive strategy that can synergistically stimulate surface chemistry and microstructures is demonstrated on the pH-responsive molecule poly(2-(diisopropylamino)ethyl methacrylate (PDPAEMA)-modified temperature-triggered shape memory polymer (SMP) arrays. The responsive PDPAEMA and SMP can provide the surface with tunable surface chemistry and microstructures, respectively. Thus, the wetting of the surface between various states can be reversibly and precisely controlled from superhydrophilicity to superhydrophobicity with contact angle (CA) differences of less than 15° under the cooperative effect between the adjustable surface microstructure and chemistry. The surface is further utilized as a platform to create gradient wettings based on its excellent controllability. Therefore, this work presents a strategy for surface wetting control by combining tunable surface microstructures and chemistry. The prepared samples with a special wetting controllability can be applied to numerous fields, including adaptive liquid microlenses, accurate drug release, and selective catalysis. This work also proposes novel expectations in designing smart functional surfaces.

Twofold bioinspiration of TiO2-PDA hybrid fabrics with desirable robustness and remarkable polar/nonpolar liquid separation performance

The fundamental relationship between microstructure, constituent, processing and performances of separating materials is really a vital issue. Traditional preparation methods for separation membranes are complex, time-consuming and easy to be fouled. Also, the durability of conventional coatings on membrane is poor. By combination of bioinspiration from mussel adhesive and fish scales’ underwater superoleophobicity, we propose a general route to prepare organic-inorganic hybrid coatings, while no complex apparatus is needed. Specifically, based on the biomimetic adhesion of polydopamine (PDA), we used it as a binder to adhere TiO2 nanoparticles and built rough microstructure on fabric. In this way, we obtained TiO2-PDA treated fabric with special wettability. These TiO2-PDA treated samples owned superamphiphilicity in air, underwater superoleophobicity (underwater oil contact angles (OCAs) > 150°), underoil superhydrophobicity (underoil water contact angles (WCAs)> 150°), excellent multiresistance; and can separate polar/nonpolar liquid mixture effectively. It also owned superaerophobicity underwater (underwater bubble contact angles (BCAs) > 150°). The proposed TiO2-PDA coatings are highly expected to be employed for real situation of water pollution remediation, self-cleaning, oil extraction and harsh chemical engineering issues.

Advanced Progress of Green Textile with Special Wettability

Advanced Progress of Green Textile with Special Wettability

Advances in the Preparation of Functional Surfaces with Special Wettability by Femtosecond Laser Ablation（Invited）

Advances in the Preparation of Functional Surfaces with Special Wettability by Femtosecond Laser Ablation（Invited）

Porous evaporators with special wettability for low-grade heat-driven water desalination

Design of novel special wettable evaporators with robust stability for high-performances porous interface distillation.

Bioinspired surfaces with special micro-structures and wettability for drag reduction: which surface design will be a better choice?

Human beings learn from creatures in nature and imitate them to solve challenges in daily life. Thus, the use of bioinspired surfaces for drag reduction has attracted extensive attention in recent years due to their important applications in many fields, such as pipeline systems, maritime transportation, and military weapons. Herein, we introduce some typical plants and animals with low drag surfaces that exist in nature, focusing on their drag reduction patterns. There are two main mechanisms to explain how surfaces reduce frictional drag, where one is to design a suitable surface geometry to change the flow distribution of surrounding fluid and the other is to introduce a low friction lubricating layer (usually air or non-toxic silicone oil) to partially or completely replace the solid-liquid interface. Hence, by mimicking these organisms, some surfaces have been fabricated to reduce frictional drag, including riblets, superhydrophobic surfaces, and slippery liquid-infused porous surfaces. With the increasing research on drag-reducing surfaces, the drag reduction rate of different types of surface designs has greatly improved in recent years. This review provides a holistic overview that facilitates direct comparisons between these surface types. To select an optimal surface for drag reduction in practical applications, the merits and deficiencies of different surface designs are analysed and compared. Finally, based on the current challenges, we present some future prospects for the application of bioinspired surfaces in drag reduction.

Cellulosic fiber filter with special wettability for efficient water/fuel oil separation

Hydrophobic/oleophilic filters have great potential for application in oil/water separation. Herein, we describe the successful preparation of environment friendly superhydrophobic cellulosic fiber filter to remove water from diesel. The modified TiO2 particles were used to fabricate the rough structure of superhydrophobic filter paper via a dip-coating method with epoxy resin as a binder. With the further dipping modification by hexadecyltrimethoxysilane (HDTMS), the filter paper obtained excellent water-resistance with water contact angle (WCA) ranging from 126.0° to 151.8°, and strong stability against acid, alkali and UV lights. In this work, it was found that the WCA was proportional to the surface roughness. The obtained hydrophobic filter papers could selectively absorb oil from water-containing fuel oil and could separate water/fuel oil mixture very efficiently with separation efficiency higher than 99%. This simple and mild strategy would inspire the large-scale fabrication of multifunctional surfaces for practical applications in water/oil separation.

Superhydrophobic, superamphiphobic and SLIPS materials as anti-corrosion and anti-biofouling barriers

Multifunctional interfacial materials with special wettability including superhydrophobic, superamphiphobic, and SLIPS exhibited promising potentials for corrosion and biofouling resistance.

Facile fabrication of micro-/nanostructured, superhydrophobic membranes with adjustable porosity by 3D printing.

Porous membranes with special wetting properties have attracted great interest due to their various functions and wide applications, including water filtration, selective oil/water separation and oil skimming. Special wetting properties such as superhydrophobicity can be achieved by controlling the surface chemistry as well as the surface topography of a substrate. Three-dimensional (3D) printing is a promising method for the fast and easy generation of various structures. The most common method for 3D printing of superhydrophobic materials is a two-step fabrication process: 3D printing of user-defined topographies, such as surface structures or bulk porosity, followed by a chemical post-processing with low-surface energy chemicals such as fluorinated silanes. Another common method is using a hydrophobic polymer ink to print intricate surface structures. However, the resolution of most common printers is not sufficient to produce nano-/microstructured textures, moreover, the resulting delicate surface micro- or nanostructures are very prone to abrasion. Herein, we report a simple approach for 3D printing of superhydrophobic micro-/nanoporous membranes in a single step, combining the required topography and chemistry. The bulk porosity of this material, which we term “Fluoropor”, makes it insensitive to abrasion. To achieve this, a photocurable fluorinated resin is mixed with a porogen mixture and 3D printed using a stereolithography (SLA) printing process. This way, micro-/nanoporous membranes with superhydrophobic properties with static contact angles of 164° are fabricated. The pore size of the membranes can be adjusted from 30 nm to 300 nm by only changing the porogen ratio in the mixture. We show the applicability of the printed membranes for oil/water separation and the formation of Salvinia layers which are of great interest for drag reduction in maritime transportation and fouling prevention.

Advanced Materials with Special Wettability toward Intelligent Oily Wastewater Remediation.

Clean water resources are essential to our human society. Oil leakage has caused water contamination, which leads to serious shortage of clean water, environmental deterioration, and even increasing number of deaths. It is of great urgency to solve the oil-polluted water problems worldwide. Efficient oil/water separation, especially emulsified oil/water mixture separation, is widely used to mitigate water pollution issues. Recently, advanced materials with special wettability have been employed for oily wastewater remediation. Moreover, by endowing them with various intelligent functions, smart materials can effectively separate complex oil/water mixtures including extremely stable emulsions. In this review, oil/water separation mechanisms and various fabrication methods of special wettability separation materials are summarized. We highlight the special wettable materials with intelligent functions, including photocatalytic, self-healing, and switchable oil/water separation materials, which can achieve self-cleaning, self-healing, and efficient oily wastewater treatment. In each section, the acting mechanisms, fabricating technologies, representative studies, and separation efficiency are briefly introduced. Lastly, the challenges and outlook for oil/water separation based on the special wettability materials are discussed.

Remarkable bactericidal traits of a metal-ceramic composite coating elated by hierarchically structured surface.

SummaryA ceramic-based coating with a hierarchical surface structure was synthesized via solid-state reaction enabled by a double cathode glow discharge technique. This innovative coating comprises two distinct layers, specifically an outer layer with a well-aligned micro-pillar array and a dense inner layer. Both are composed of a face-centered cubic Cu(Co,Ni,Fe) solid solution phase together with a spinel-type Fe(Al,Cr)2O4 oxide. This coating exhibits superhydrophobicity and, yet, a very strong adhesion to water, i.e., the so-called “rose petal effect”. This coating also exhibits highly efficient antibacterial ability against both Staphylococcus aureus and Escherichia coli bacteria under both dark and visible light conditions. The excellent antibacterial property originates from the synergistic effects through the release of Cu ions coupled with photothermal activity upon light activation.

Developing a new superhydrophilic and superoleophobic poly(4-(1-vinyl-1H-imidazol-3-ium-3-yl) butane-1-sulfonate): vinyl imidazole@Perfluorooctanoic acid@SiO2 coated stainless steel mesh for highly efficient, stable, and durable oil/water separation

The design and development of efficient approaches for water–oil separation have had widespread interest. Most previously introduced techniques and materials used for development of the successful separation of oily wastewater could not answer all the desired demands, such as being efficient and environmentally and economically friendly. Therefore, in seeking a novel method capable of answering these expectations, surfaces with special wettability were introduced. A novel, reusable, and recyclable superhydrophilic and superoleophobic poly(Vsim-Vim)@PFOA@SiO2 nanocomposite-coated stainless steel mesh was synthesized through a facile preparation process. Since the most important factors of these coatings are their oleophobicity and hydrophilicity values, the water contact angle (WCA) and the oil contact angle (OCA) were measured. The coating indicated the excellent characteristics in which the results showed that WCA was 0°, while OCA was 142°, which confirmed remarkable superhydrophilicity and superoleophobicity, respectively. It is worth mentioning that the coating owes its surface behavior mainly to the finer size of mesh and formation of silica, which causes the higher roughness and better oleophobicity, reduction of the surface energy of the synthesized poly(Vsim-Vim)@SiO2 nanocomposite by PFOA, the formation of hierarchical micro-nanometer scale roughness structures on the coating surface, and stable adhesion of SiO2 nanoparticles into poly(Vsim-Vim). Eventually, superb oil/water separation efficiency of 95% with high stability was attained. This result implied that the fabricated coating is a suitable candidate for water–oil emulsion separation which can potentially be employed in green industrial applications. Also, we believe this approach provides a potential application in controllable oil/water separation in large volumes.

One-step fabrication of brass filter with reversible wettability by nanosecond fiber laser ablation for highly efficient oil/water separation

Recently with the development of industries and maritime oil transportation, water pollution due to frequent oil spilling has become a worldwide challenge. So, the fabrication of materials with special wettability and application in oil-water separation has attracted considerable attention. In the present study, a simple one-step method without any chemical modification is reported to fabricate the brass mesh using brass sheet drilling with a commercial nanosecond fiber laser system. Laser ablation creates hierarchical micro/nano structures by plasma created at the irradiated point. The morphology, elemental map and crystal structure of the pristine and drilled brass were analyzed by AFM, FE-SEM, EDS and XRD techniques. Wettability of fabricated brass mesh changes from superhydrophilic to highly hydrophobic (water contact angle 140°) after laser ablation and exposing to ambient conditions. Also, the obtained highly hydrophobic sample can switches to a superhydrophilic by thermal treatment. Then the superhydrophilic surface can switches again to the highly hydrophobic surface by exposuring to the air for several days. The reasons for wettability switching were discussed in details. The prepared brass mesh with uniform holes can be used as a filter for efficient separation of various organic solvents from water in many cycles without decreasing in its separation capability.

Superhydrophobic magnetic hollow carbon microspheres with hierarchical micro/nano-structure for ultrafast and highly-efficient multitasking oil-water separation

Nowadays, developing separation materials for oil-water mixture and even emulsion have drawn extensive interest, with increasing oily wastewater pollution. Among kinds of separation materials, hydrophobic magnetic particles can rapidly and high-efficiently separate oil from either oil-water mixtures or emulsions. However, they not only commonly suffer from complicated preparation procedures and poor resistance to harsh conditions, but also are almost unable to satisfy the demand of multitasking separations towards oil-water mixtures and micro/nanoemulsions with surfactant. Herein, a facile, simple and scalable approach is introduced to prepare superhydrophobic magnetic hollow carbon microspheres (SMHCMs) with micro/nano hierarchical surface. Thanks to the special wettability properties, micro/nano hierarchical surface, nano-porous shell and hollow cores, the as-prepared SMHCMs show an unprecedented absorption capacity of over 10 g/g for oil-water mixtures within an absorption time of 60 s as well as a superior separation efficiency of near 99% for surfactant-free and surfactant-stabilized micro/nanoemulsions at an extremely short time of as low as 10 s. In addition, the SMHCMs also possess stable performance, good reusability, durability and resistance to harsh environments (e.g., acidic, alkaline and high-saline). This work proposes a new prospect for designing advanced materials applied to the fast and highly-efficient oil-water separation.

Facile fabrication of super-hydrophilic cellulose hydrogel-coated mesh using deep eutectic solvent for efficient gravity-driven oil/water separation

The development of sustainable, low-cost, green and efficient oil–water separation materials is an attractive and challenging work. Oil/water separation process has been achieved by a variety of materials with special wettability, but most materials require complex instruments or involve toxic and corrosive chemicals, which might lead to some potential economic and environmental issues. Our work proposed here is a novel super-hydrophilic, underwater super-oleophobic cellulose hydrogel-coated mesh (CHCM) which produced by deep eutectic solvent, aimed for efficient gravity-driven oil/water separation. Based on this pre-wet CHCM, the separation efficiency of various oil–water mixtures was above 98.0%, and the results also showed that CHCM has good recyclability and durability, even after 20 cycles, the separation efficiency also maintained at 98.5%. Impressively, the prepared CHCM also exhibited good salt resistance; it can separate a high efficiency pump oil mixture from a saturated aqueous NaCl solution. Through XPS analysis of CHCM, the oil–water separation mechanism is due to the large number of super-hydrophilic groups on its surface. This simple, green, and efficient method overcomes an important barrier to the safe separation of oil–water mixtures and provides insights into the design of advanced materials for practical oil–water separation.

Environment-responsive coatings with recoverable in-air superamphiphobicity and underwater superoleophobicity

Creating a surface that is simultaneously amphiphobic in air and oleophobic in water is energy unfavorable. To overcome this counterintuitive scientific problem, we demonstrate a general approach for construction of environment-responsive coatings made of perfluorinated surfactant substituted polyelectrolyte multilayers (PEMs). Sum frequency generation (SFG) vibrational spectroscope indicates that in an air environment, the film coatings orderly protrude their hydrophobic perfluorinated tails into air to decrease surface energy, giving rise to amphiphobicity with water and hexadecane contact angles (CAs) of ~114° and ~65° respectively on flat substrates. When the coated substrates are placed in water, the coatings will undergo a reconfiguration, the perfluorinated chains of the coatings instantaneously migrate and embed themselves into the film bulk to optimize their surface energy, leaving hydrophilic portions and positively charged groups exposed at the film-water interface (confirmed by surface zeta potential, XPS and SFG), which leads to an underwater oleophobicity with hexadecane CA of ~147°. By applying the coatings on roughed substrates, e.g., fabrics, both superamphiphobicity and underwater superoleophobicity were achieved with in-air water and hexadecane CAs of ~155° and ~152°, and underwater hexadecane CA of ~169°, respectively. Moreover, the coatings with these special wettabilities exhibit a good self-healing performance upon both plasma-induced surface decomposition and salt treatment. These coatings may bring in new insights of surface wettability and offer great potential in self-cleaning, anti-oil-fouling both in air and water (especially for aquatic devices working in oil spill situations).

Influence of RF Plasma Jet Surface Treatment on Wetting Behavior of Yttria Stabilized Zirconia SPS Coatings

According to the value of water contact angle (WCA), the surfaces can be roughly defined as hydrophilic (with WCA less than 90°) or as hydrophobic (with WCA higher than 90°). Water wetting behavior plays important role and surfaces with special wettability (hydrophobic-superhydrophobic; hydrophilic-superhydrophilic) can be used both in the daily life (solar cells, smartphones, car windows, etc.) and in the industry (corrosion resistance, self-cleaning, anti-icing properties, etc.). Nowadays, the development of hydrophobic surface treatment that may be applied in the industry is very interesting topic. Therefore, it was decided to estimate the influence of radiofrequency (RF) plasma jet in atmosphere on wetting behavior of ceramic plasma sprayed coatings. As the initial material for surface treatment, yttria stabilized zirconia suspension plasma sprayed coatings were used. The influence of RF plasma jet on suspension plasma sprayed coatings was estimated on both hydrophilic and hydrophobic surfaces, and resulted water contact angle and free surface energy of modified samples were measured by sessile droplet method. Microstructure, phase composition and topography investigation were carried out by means of light microscopy, X-ray diffraction techniques and non-contact profilometry.

Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application

Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Re...

Phosphate solution wetting of graphite blocks for magnesium electrolysis to enhance their oxidation resistance. Part 1

Graphitized electrodes are broadly used in industry. However, when they are used in high-temperature operating environments, they are subject to oxidation, which can lead to abnormal operation or premature failure of an electrolytic cell. Use of protective coatings or special wetting solutions (melts) help increase the oxidation resistance of a wide assortment of components. It is obvious that a coating that covers an electrode completely will hinder or stop the electric current from flowing at the electrode/electrolyte boundary, which makes this technique inapplicable to anodes for magnesium electrolysis. Aqueous solutions of phosphates are widely used around the world to make materials more resistant to high-temperature oxidation due to the formation of glassy phases during drying. This paper examines the efficiency of using a mixture of zinc and aluminium dihydrophosphates dissolved in an aqueous solution of orthophosphoric acid to enhance the oxidation resistance of the graphite electrode EGP (NR). A comprehensive thermal analysis was carried out to examine the solution for suitability. And X-ray diffractometry helped verify the formation of crystals after the solution had been dried. Cube-shaped specimens with the side length of 50 mm were used in the experiments aimed at identifying optimum graphite wetting and drying conditions. Isopropanol was used as a surfactant to ensure proper wetting. The specimens were first subjected to vacuum degassing for air to be removed from the pores, and then they were soaked in a rarefied solution. A kinetic model was selected to describe the post-wetting drying procedure. The oxidation resistance was analyzed in a dynamic air flow. The experiments were carried out at 700 oC as it is the highest possible temperature for magnesium electrolysis. The results of the experiments showed that the above wetting technique, when applied in a laboratory environment, helped achieve a five-fold increase in the oxidation resistance of the model graphite electrodes. The authors looked at the feasibility of scaling the experiments and developing process circuits to produce graphite with high oxidation resistance.

Underwater Superoleophobic Matrix-Formatted Liquid-Infused Porous Biomembranes for Extremely Efficient Deconstitution of Nanoemulsions.

Wettability is one of the most critical interfacial properties of any surface. Surfaces with special wettability such as superwetting or superantiwetting are being intensively explored for their wide-ranging applicability by a biomimetic exploration of unusual wetting phenomena in nature. This study provides a green water-infused superoleophobic composite membrane by boosting bacteria nanocellulose growth on a reinforcement fibrous substrate. It was shown that this versatile antifouling membrane is capable of removing water from surfactant-stabilized oil-in-water micro/nanoemulsions and helps to isolate the oil fraction with very high filtration efficiency. The renewable membrane based on bacteria nanocellulose matrices can vastly improve current technologies by cultivating a naturally occurring soft materials approach with lubricious conformal interfaces to effectively and simply cover suitable surfaces.