Superhydrophobic Research Articles

Facile Preparation of Durable Superhydrophobic Coating by Liquid-Phase Deposition for Versatile Oil/Water Separation

Serious damage caused by oily wastewater makes the development of efficient superhydrophobic and superoleophilic materials for oil/water separation processes critical and urgent. Herein, durable superhydrophobic nanometer-scale TiO2 grains with low-surface-energy substance composite-modified materials were fabricated by using a cost-effective and facile synthesis method for the gravity-driven separation of oil/water mixtures under harsh conditions. Different substrates, such as sawdust, wheat straw, cotton, sponge and fabric, were applied for superhydrophobic surface preparation, and various low-surface-energy reagents could interact with deposited TiO2 nanoparticles, including cetylamine, dodecanethiol, stearic acid and HDTMS. The resultant materials showed superhydrophobic properties with a water contact angle (WCA) higher than 150.8°. The separation of various oil/water mixtures with high efficiency and purity was acquired by using the as-prepared sponge. More importantly, the coated sponge exhibited good resistance to various harsh environmental solutions. Moreover, its superhydrophobicity also remained even after 12 months of storage in air or 10 cycles of abrasion. The durable superhydrophobic coating prepared in this work could be practically used for the highly efficient separation of oil/water mixtures under various harsh conditions.

A practical approach to emulsify silicone oil and attaining superhydrophobic fabrics

A practical approach to emulsify silicone oil and attaining superhydrophobic fabrics

Spray-Drying Hydrophobic Cellulose Nanocrystal Coatings with Degradable Biocide Release for Marine Antifouling.

With increasing awareness about the ecological environment, increased attention has been paid to the application of eco-friendly materials in the field of marine antifouling. In this work, a novel coating having good mechanical strength and static marine antifouling characteristics was fabricated using cellulose nanocrystals (CNCs) as the skeleton material, with in situ growth of SiO2 as the basic superhydrophobic material and introducing hexadecyl trimethyl ammonium bromide (CTAB) and 4-bromo2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile (Econea) into the coating. Due to the high strength and rod structure of CNCs, the coating maintained super-hydrophobicity after 50 cycles of abrasion tests. Moreover, the addition of CTAB during the synthesis of SiO2 led to the hydrolysis and polycondensation of tetraethyl orthosilicate at the micellar interface. Econea was fully mixed with SiO2 nanoparticles, thus slowing down the rate of release of Econea. Meanwhile, the adhesion between the coating and the substrate reached 1.9 MPa, which can meet the application requirements for marine environments. The bioassay using bacteria (Escherichia coli) and diatoms (Nitzschia closterium) showed that the rate of inhibition of the coating on bacteria and diatoms could reach 99 and 90%, respectively, after immersion in artificial seawater for 28 days. This research provides a facile and promising fabricating solution of an eco-friendly CNC-based coating having strong antifouling characteristics suitable for marine environments.

TiO2/PDMS hybrid system for constructing superhydrophobic surfaces of cotton fabrics with resistance to droplet adhesion

Purpose This study aims to produce a superhydrophobic fabric surface with a layered rough structure and which are resistant to droplet adhesion. Polydimethylsiloxane (PDMS) systems doped with stearic acid modified titanium dioxide (SA-TiO2) nanoparticles was sprayed onto the surface of cotton fabric. Design/methodology/approach This experiment therefore uses a simple method to prepare superhydrophobic textiles by spraying SA-TiO2 particles mixed with PDMS onto the surface of cotton fabrics. The effects of the ratio of stearic acid to TiO2, spraying times and tension on the apparent morphological structure and hydrophobic properties of the cotton fabric were investigated. Findings The results showed that the stearic acid-modified TiO2 nanoparticles were hydrophobic and more uniformly dispersed in the PDMS solution. When the modification ratio of stearic acid to TiO2 was 3:5, the water contact angle of cotton fabric was 155.48° and sliding angle was 6.67° under the applied tension for three times of spraying, showing superhydrophobicity. The fabric shows super hydrophobic and anti-adhesive properties to a wide range of liquids such as cola, dyeing liquids, tea, milk and simulated blood. The surface tension of the liquid shows a negative correlation with its adhesion to the fabric. Research limitations/implications The SA-TiO2 and PDMS were applied to the fabric surface by spraying, which not only gave the fabric superhydrophobic properties, but also created anti-adhesion to a wide range of droplets. Practical implications The superhydrophobic cotton fabrics prepared by this method showed good anti-adhesive behavior to common stains and simulated blood and can be used in the development of medical protective textiles. Originality/value Modification of TiO2 with stearic acid to prepare SA-TiO2 with excellent hydrophobic properties, which was mixed with PDMS to make suspensions. Fluorine-free superhydrophobic fabrics were prepared by spraying method. It also exhibited excellent anti-adhesive properties against blood, providing a reference for the preparation of self-cleaning and anti-adhesive surgical gowns.

Characterization and Superhydrophobic Anticorrosive Coating of AA-7475/ZrO2/Polymer Nanocomposites

An AA-7475 is coated with superhydrophobic (SH) polymer nanocomposites (PNCs), emphasizing the coating’s manufacturing, characterization, and anticorrosive qualities. Coating AA-7475 alloy with polyvinyl chloride (PVC), copper stearate (CS), and zirconium oxide (ZrO2) nanoparticles produces the desired superhydrophobic. Using an X-ray diffractometer, field-emission scanning electron microscopy, Fourier-transform infrared spectrometer, ZrO2 nanoparticles, CS, and PVC PNCs are analyzed structurally and molecularly. The atomic force microscope picture was analyzed to determine how the surface roughness affected the SH behavior reached by changing the weight percentage of ZrO2 nanoparticles from 0.6 to 3.0 wt%. PNC-5 with 3.0 wt% ZrO2 nanoparticles is used as resistance to corrosion coating for AA-7475 due to its water contact angle of 154°. In a 3.5% NaCl solution, uncoated and PNC-5-coated AA-7475 are examined using potentiodynamic polarization and electrochemical spectroscopy. PNC-5 coating reduces AA-7475 corrosion rate from 23.75 to 0.2253 mpy. In this study, we use polarization resistance, corrosion resistance efficiency, double layer capacitance, corrosion current density, and charge transfer resistance to demonstrate that the SH surface air trapping phenomena are responsible for effective corrosion resistance.

Biocompatible superhydrophobic surface on Zr-based bulk metallic glass: Fabrication, characterization, and biocompatibility investigations

Superhydrophobic metal materials are promising candidates for preparing the precision blood-contacting medical devices. Finding a metal material with excellent biocompatibility and superplastic forming ability to fabricate superhydrophobic surface is of great practical significance. Zr-based bulk metallic glass with high glass-forming ability was selected as the experimental sample. Micro-nano hierarchical structure was etched by electrochemical method in the ultrasonic environment, and the superhydrophobic surface with good biocompatibility was obtained after further modification. Electrochemical polarization tests show that the superhydrophobic surface can maintain long-term corrosion resistance in simulated body fluids. Blood and cell tests indicate that the superhydrophobic sample has an extremely rate of hemolysis and exhibits the ability to effectively inhibit the adhesion of platelets and smooth muscle cells. In addition, the superhydrophobic sample surface also exhibits good mechanical durability and chemical stability. This study offers a new perspective on the application of Zr-based bulk metallic glass in blood-contacting medical devices.

A Novel Anti-Flashover Superhydrophobic Coating with Self-Assembly Characteristic of Surface Energy Differences.

Because of the versatility of superhydrophobic materials, they have attracted a lot of attention even in power electronics, transportation, engineering, and other fields. The volume fraction of fluorinated silicon oxide nanoparticles in superhydrophobic materials is one of the most important factors. Increasing the volume fraction will decrease the stability between the coating and the hydrophobic surface. Especially, the flashover voltage of the coating gradually decreases from 10 to 35vol.%. Meanwhile, the flashover voltage dispersion of the coating increases drastically after 30vol.%. In order to improve the electrical properties of the superhydrophobic coating, self-assembly of surface energy differences strategy is proposed in this work. A binary filling phase of the coating is introduced by 2D boron nitride nanosheets and silicon oxide nanoparticles. Although Hexagonal boron nitride with high surface energy and low roughness, it will be spontaneously assembled and wrapped by silicon oxide nanoparticle based on surface energy differences, which forming a low surface energy filled phase. Experiment results prove that the flashover voltage of the superhydrophobic coating is optimized by the binary filling phase coating. This method offers new ideas for the selection of filling phase and application of superhydrophobic materials.

Preparation of Superhydrophobic Cotton Fabric with Ultraviolet Resistance and Photocatalysis Based on CuS/Reduced Graphene Oxide

AbstractIn the present study, the superhydrophobic cotton fabrics with ultraviolet (UV) resistance and photocatalytic properties were fabricated by polydimethylsiloxane (PDMS) and CuS/reduced graphene oxide (RGO). The CuS/RGO particles enhanced the surface roughness, and PDMS was used to reduce the surface energy of cotton fabrics and increase the adhesion of CuS/RGO particles to cotton fabrics. The water contact angle (WCA) of coated cotton fabrics could reach ∼158.4°, endowing the fabrics with excellent self‐cleaning and oil‐water separation properties. It is confirmed that cotton fabric can obtain superhydrophobic property by adjusting the concentration of CuS/RGO and PDMS. Thanks to the good photocatalytic activity and excellent ultraviolet absorption capacity of the composite material, the superhydrophobic fabrics possessed outstanding ultraviolet resistance with the maximum UV protection factor (UPF) of 851.2 and photocatalytic performance with the photocatalytic degradation rate of methylene blue 92 %. Furthermore, the prepared cotton fabric retained superhydrophobicity after 90 h UV irradiation or 2000 cycles rubbing. The flexible superhydrophobic cotton fabrics with UV protection had promising application prospects in various fields.

Viscoplastic flows in thin superhydrophobic channels

Via numerical computations, we study plane Poiseuille flow of a viscoplastic fluid in channels with the presence of a superhydrophobic (SH) groovy lower wall, where air is trapped inside the SH wall cavities. We assume this liquid/air interface to be flat while it is pinned at the groove edges. Our main focus is on the thin channel limit, for which the channel height is typically smaller than the groove period. To quantify the viscoplastic rheological behaviour, we rely on the Bingham model, via the Papanastasiou regularization method. We consider a no-slip boundary condition at the liquid/solid contacts while we model the liquid/air interface boundary using the Navier slip law. Focusing on the creeping flow limit (i.e. the Reynolds number is fixed to R=0.01), our main flow parameters are the Bingham number (B), the slip number (b), the groove periodicity length (ℓ), and the slip area fraction (φ). Our computational results quantify the effects of these parameters on the flow velocity fields, the unyielded plug zones and their areas, the effective slip lengths, and the friction factors. The shape of the unyielded plug zones are captured, allowing us to classify our flows into four main regimes, based on the characteristics of the unyielded zones, in particular the presence/absence of a broken center plug and/or an SH wall plug. We also find that the effective slip length generally increases with an increase in b, converging to a profile once an SH wall plug appears. Finally, the friction factor decreases with an increase in b, especially at larger B.

Design of Waterborne Superhydrophobic Fabrics with High Impalement Resistance and Stretching Stability by Constructing Elastic Reconfigurable Micro-/Micro-/Nanostructures

Superhydrophobic fabrics have great application potential in many fields including wearable electronic devices, sports textiles, and human health monitoring, but good water impalement resistance and stretching stability are the prerequisites. Here, we report the design of waterborne superhydrophobic fabrics with high impalement resistance and stretching stability by constructing elastic reconfigurable micro-/micro-/nanostructures. Following theoretical analysis, two approaches were proposed and employed: (i) regulating distance between the microfibers of polyester fabrics to decrease the solid-liquid contact area, and (ii) forming reconfigurable two-tier hierarchical micro-/nanostructures on the microfibers by stretching during dipping to further decrease the solid-liquid contact area. The effects of microfiber distance and micro-/nanostructures on microfibers on superhydrophobicity and impalement resistance were studied. The superhydrophobic fabrics show excellent impalement resistance as verified by high-speed water impact, water jetting, and rainfall, etc. The fabrics also show excellent stretching stability, as 100% stretching and 1000 cycles of cyclic 100% stretching-releasing have no obvious influence on superhydrophobicity. Additionally, the fabrics show good antifouling property, self-cleaning performance, as well as high abrasion and washing stability. The experimental results agree with the theoretical simulation very well. We anticipate that this study will boost the development of impalement-resistant and stretching-stable superhydrophobic surfaces.

Sustainability of the plastron on nano-grass-covered micro-trench superhydrophobic surfaces in high-speed flows of open water

This paper studies the sustainability of plastrons on superhydrophobic (SHPo) surfaces made of longitudinal micro-trenches covered by nano-grass with the main interest on hydrodynamic friction drag reduction in high-speed flows of open water, which represent the operating conditions of common watercraft. After revising the shear-driven drainage model to address the air diffusion for SHPo surfaces, the existing theories are combined to reveal the trends of how the immersion depth, air saturation level and shear stress affect the maximum attainable plastron length. Deviations from the theories by the dynamic effect at the two ends of the trench, the interfacial contaminations and turbulent fluctuation are also discussed. A combinatorial series of well-defined SHPo trench surfaces (4 cm × 7 cm in size with varying trench widths, depths, lengths and roughnesses) is microfabricated and attached underneath a 4 m long motorboat on seawater in turbulent flows up to 7.2 m s−1(shear rate ∼83 000 s−1and friction Reynolds number ∼5500). Because the plastron can provide a substantial slip only while its air–water interfaces are pinned (or only slightly depinned) at the trench top, two underwater cameras are employed to differentiate the pinned (and slightly depinned) interfaces from the depinned (and no) interfaces. In addition to achieving pinned plastrons on 6 cm long trenches aligned to high-speed flows in open water, the experimental results corroborate the theoretical estimations, supporting the design of SHPo surfaces for field applications.

Ultra-superhydrophobic MOFs coated on polydopamine-modified polyethylene terephthalate for efficient removal of particulate matter

To achieve ultra-low emissions in industrial flue gas, three different micro/nano metal–organic-framework (MOF) crystals (NH2-MIL-125, ZIF-8 and HKUST-1), as active purification units, were assembled on polydopamine (PoDA)-modified PET fibers (p-PET) by rapid, efficient, and supramolecular self-polymerization at room temperature to construct a novel superhydrophobic composite filter material (SH-Mp-PET(Ti, Zn, Cu)). The wrinkle structure and dielectric constant on the surface of SH-Mp-PET(Ti, Zn, Cu) filter fiber were improved by the synergistic effect of PoDA and MOF, and the charge effect on the surface of the three composite filter materials was improved, so that the electrostatic interaction between the fiber and the particles was improved. At the same time, the porous structure within the MOF did not result in significant pressure loss, and the purification quality factor (QF) of ultra-fine PM was significantly improved by the dual modification of RE and ΔP. The QF of three SH-Mp-PET(Ti, Zn, Cu) filter media were 22.9 %, 29.6 % and 28.1 % higher than PET, respectively. And SH-Mp-PET exhibited good thermal and mechanical stability. This approach can promote the development of industrials flue gas superhydrophobic filter materials and provides a new concept for developing MOF materials for flue gas treatment and reuse.

Smart and durable pH-responsive superhydrophobic fabrics with switchable surface wettability for high-efficiency and complex oil/water separation

The oily wastewater has posed a great threat to the environment and human health, and the oil-water mixture is complex and diverse. Therefore, it is crucial to develop a smart and efficient oil/water separation material. In this paper, random polymers containing carboxyl groups were synthesized for surface-modifying hydrophilic SiO2 nanoparticles. Polydimethylsiloxane (PDMS) was then used as the adhesive to fix the modified SiO2 nanoparticles firmly on the fabric surface endowing the fabric with a robust hydrophobic effect. The modified SiO2 nanoparticles not only made the fabric obtain a rough structure but also caused the fabric to have the effect of switchable wettability under the stimulation of pH. In addition, the prepared fabric maintained good mechanical durability and chemical stability after the mechanical abrasion, ultraviolet irradiation, and organic solvent treatment. Interestingly, under the stimulation of pH, the smart fabric could controllably separate different oil/water mixtures (including heavy oil/water and light oil/water) with excellent separation efficiency and high flux even after 20 cycles of separation process. Meanwhile, the pH-responsive fabric material successfully separated light oil/water/heavy oil three-phase oil/water mixture and different kinds of emulsions. Therefore, the prepared pH-responsive superwetting fabric has a broad application prospect in the field of dealing with complex oil/water mixing systems.

Scalable Fabrication of Superhydrophobic Coating with Rough Coral Reef-Like Structures for Efficient Self-Cleaning and Oil-Water Separation: An Experimental and Molecular Dynamics Simulation Study.

Superhydrophobic coating has a great application prospect in self-cleaning and oil-water separation but remains challenging for large-scale preparation of robust and weather-resistant superhydrophobic coatings via facile approaches. Herein, this work reports a scalable fabrication of weather-resistant superhydrophobic coating with multiscale rough coral reef-like structures by spraying the suspension containing superhydrophobic silica nanoparticles and industrial coating varnish on various substrates. The coral reef-like structures effectively improves the surface roughness and abrasion resistance. Rapid aging experiments (3000h) and the outdoor building project application (3000 m2 ) show that the sprayed superhydrophobic coating exhibits excellent self-cleaning properties, weather resistance, and environmental adaptability. Moreover, the combined silica-coating varnish-polyurethane (CSCP) superhydrophobic sponge exhibits exceptional oil-water separation capabilities, selectively absorbing the oils from water up to 39 times of its own weight. Furthermore, the molecular dynamics (MD) simulation reveals that the combined effect of higher surface roughness, smaller diffusion coefficient of water molecules, and weaker electrostatic interactions between water and the surface jointly determines the superhydrophobicity of the prepared coating. This work deepens the understanding of the anti-wetting mechanism of superhydrophobic surfaces from the perspective of energetic and kinetic properties, thereby paving the way for the rational design of superhydrophobic materials and their large-scale applications.

Natural microfibrils/regenerated cellulose-based carbon aerogel for highly efficient oil/water separation

Cellulose-based carbon aerogels as biodegradable and renewable biomass materials have presented potential applications in oil/water separation. Herein, a novel carbon aerogel composed of natural microfibrils/regenerated cellulose (NM/RCA) was directly prepared by economical hardwood pulp as raw material using a novel co-solvent composed of deep eutectic solvent (DES) and N-methyl morpholine-N-oxide monohydrate (NMMO·H2O). In addition, the morphology and structure of the filiform natural microfibers could be remained after carbonized at 400 ℃, which resulted in a low density (8–10 mg cm−3), high specific surface area (768.89 m2 g−1) and high sorption capability. In addition, the aerogel exhibited high compressibility, outstanding elasticity, excellent fatigue resistance, and recyclability (80.5% height recovery after repeating 100 cycles at the strain of 80%). Due to the morphology and composition of the carbonized microfiber surface, the superhydrophobic materials with a water contact angle of 151.5°, could sorb various oils and organic solvents with 65–133 times its own weight and maintain 91.9% sorption capacity after 25 cycles. In addition, the aerogels could achieve the continuous separation of carbon tetrachloride (CCl4) from water with a high flux rate of 11,718.8 L m−2 h−1. Therefore, our prepared NM/RCA aerogels are anticipated to have broad potential applications in oil purification and contaminant remediation.

Self-ejection of salts and other foulants from superhydrophobic surfaces to enable sustainable anti-fouling.

A recently discovered phenomenon in which crystalline structures grown from evaporating drops of saline water self-eject from superhydrophobic materials has introduced new possibilities for the design of anti-fouling materials and sustainable processes. Some of these possibilities include evaporative heat exchange systems using drops of saline water and new strategies for handling/processing waste brines. However, the practical limits of this effect using realistic, non-ideal source waters have yet to be explored. Here, we explore how the presence of various model aquatic contaminants (colloids, surfactants, and calcium salt) influences the self-ejection phenomena. Counterintuitively, we find that the addition of "contaminant" chemistries can enable ejection under conditions where ejection was not observed for waters containing only sodium chloride salt (e.g., from smooth hydrophobic surfaces), and that increased concentrations of both surfactants and colloids lead to longer ejection lengths. This result can be attributed to decreased crystallization nucleation time caused by the presence of other species in water.

Magnetically responsive and durable super-hydrophobic melamine sponge material

Magnetically responsive and durable super-hydrophobic melamine sponge material

Processing and properties of a graphene-reinforced superhydrophobic siloxane

Three-dimensional superhydrophobic materials are characterized by a low surface energy and extremely low strength, and hence require reinforcement for viable applications. An experimental study is presented of the processing and mechanical properties of a graphene-reinforced superhydrophobic siloxane, synthesized by a sol–gel approach integrating alkali activation of metakaolin, hydrolysis of alkoxysilane, dispersion of graphene into the precursor, and co-condensation. To promote uniform dispersion and distribution of graphene, three processing techniques were used: while ultrasonication was adopted to disperse graphene nanoplatelets, accelerated condensation at 50 and 75 °C and varying the precursor’s viscosity used to prevent graphene from floating and re-aggregation. Results of nanoindentation, porosimetry, and unconfined compression show that adding 0.9 wt% graphene increases the strength of the superhydrophobic composites from ∼ 0 to 34 MPa. Slow condensation and curing at 25 °C allow graphene to re-aggregate and float upward in the sol, leading to its heterogeneous distribution. Despite its function in improving microscale dispersion, ultrasonication detrimentally decreases the composite’s strength due to acoustic cavitation. Similarly, curing at elevated temperatures accelerates co-condensation and results in a more uniform distribution of graphene, but induces thermal cavitation and bubble formation, because the threshold for acoustic and thermal cavitations is significantly reduced by superhydrophobicity.

Preparation and Rheological Properties of Paper-Based Superhydrophobic Materials

Preparation and Rheological Properties of Paper-Based Superhydrophobic Materials

Fabrication of Robust and Effective Oil/Water Separating Superhydrophobic Textile Coatings.

A superhydrophobic (SH) surface is typically constructed by combining a low-surface-energy substance and a high-roughness microstructure. Although these surfaces have attracted considerable attention for their potential applications in oil/water separation, self-cleaning, and anti-icing devices, fabricating an environmentally friendly superhydrophobic surface that is durable, highly transparent, and mechanically robust is still challenging. Herein, we report a facile painting method to fabricate a new micro/nanostructure containing ethylenediaminetetraacetic acid/poly(dimethylsiloxane)/fluorinated SiO2 (EDTA/PDMS/F-SiO2) coatings on the surface of a textile with two different sizes of SiO2 particles, which have high transmittance (>90%) and mechanical robustness. The different-sized SiO2 particles were employed to construct the rough micro/nanostructure, fluorinated alkyl silanes were employed as low-surface-energy materials, PDMS was used for its heat-durability and wear resistance, and ETDA was used to strengthen the adhesion between the coating and textile. The obtained surfaces showed excellent water repellency, with a water contact angle (WCA) greater than 175° and a sliding angle (SA) of 4°. Furthermore, the coating retained excellent durability and remarkable superhydrophobicity for oil/water separation, abrasion resistance, ultraviolet (UV) light irradiation stability, chemical stability, self-cleaning, and antifouling under various harsh environments.