Stable Superhydrophobic Surface Research Articles

A Route towards Durable Underwater Stable Superhydrophobic Surfaces: PET-Reinforced Candle Soot Layers

Superhydrophobic coating is widely used due to its waterproof and self-cleaning properties. Carbon soot (CS) nanoparticles are naturally superhydrophobic and non-toxic which are superior to other superhydrophobic coating. However, the weak binding force of the CS nanoparticle layers hinders their practical application. In this study, micro-nanostructured PET-CS superhydrophobic coatings were prepared by a simple method. The obtained coatings presented durable superhydrophobicity and underwater stability, which are superior to PDMS-CS coatings and CS layers. The coating surfaces demonstrated superhydrophobicity under a water pressure of 13.72 kPa for up to 16 days. The surface could withstand water flush for more than 15 min. The coatings also demonstrated good mechanical stability and maintained superhydrophobicity after an abrasion length of 8 m. The stable long-lasting underwater superhydrophobic surface is of great importance for marine applications.

Multifunctional polypyrrole/MXene-wrapped sponge with synergistic solar and joule-heating effect for efficient adsorption and all-weather recovery of crude oil

Offshore oil leakage can cause huge economic losses and seriously disrupt the ecological balance. A novel approach to all-weather recovery of crude oil with high viscosity is achieved through day and night workto ensurefaster recovery. Herein, polypyrole (Ppy) covalently integrated with MXene nanosheet was connected to the melamine sponge (MS) by physico-chemical cross-linking method, exhibiting a crude oil absorbent with outstanding photothermal and electrothermal conversion performance (78.9 ℃ under 1.0 kW/m2, 62.3 ℃ in 5 V). The stable superhydrophobic surface (WCA≈153.4°), combined with the dual-energy conversion properties of absorbent provides the synergistic effect for efficient crude oil recovery performance. This is demonstrated by the fact that the maximum surface temperature can be heated to 87.0 ℃ in 3 min, and the absorption weight of crude oil to be improved to 14.26 g in 10 min. Additionally, the Ppy/MXene-wrapped sponge has high thermal stability and flame-retardant properties. Therefore, this functional absorbent has promising way for the disposal of offshore crude oil.

Underwater Bionic Self-Healing Superhydrophobic Coating with the Synergetic Effect Of Hydrogen Bonds and Self-Formed Bubbles.

The self-healing ability of superhydrophobic surfaces in air has attracted tremendous additions in recent years. Once the superhydrophobic surface is damaged underwater, water seeps into gaps among micro/nano structures. The air film diffuses into water and eventually disappears during immersion without actively replenishing the gas, which results in the impossible of self-healing. Here, an underwater self-healing superhydrophobic coating with the synergetic effect of hydrogen bonds and self-formed bubbles via the spraying method is fabricated. The movement of hydrogen bonds of the prepared polyurethane enables microstructures to reconstruct at room temperature and self-formed bubbles of effervescent materials underwater actively replenish gas before microstructures completely self-healing, achieving the self-healing property of the superhydrophobic coating. Moreover, the hydrophilic effervescent material is sprayed along with unmodified micron-scaled particles because modified nano-scale particles are key factors for the realization of superhydrophobic coating. An underwater stable superhydrophobic surface with pressure resistance (4.9kPa) is demonstrated. This superhydrophobic coating also shows excellent drag reduction, anti-icing, and anti-corrosion properties. This facile and scalable method offers a new route that an underwater self-healing superhydrophobic coating executes the gas film recovery.

Fast Fabrication of Superhydrophobic Copper Alloy Fabricated by Commercial Fiber Laser-1062 nm and Stability of Superhydrophobic Surface

We present a fast, straightforward fabrication method to produce stable superhydrophobic copper alloy surfaces. The technique consists of irradiating copper with a fiber laser and then coating the surface with ethanol. The laser ablation generates surface morphology on the copper surfaces, such as line and grid patterns. We can modify the wetting properties and surface morphology by changing the step size. We assessed the change of the water contact angle on the raw surface, laser-based textures after natural aging, and laser-based textures post-low annealing. After that, we measured the stability of the water contact angle till 120 days. After low annealing heat treatment, water contact angles on grid pattern surfaces have superhydrophobic surfaces and are more stable till 120 days.

Fabrication of a sustainable superhydrophobic surface of Ag-NPs@SA on copper alloy for corrosion resistance, photocatalysis, and simulated distribution of Ag atoms.

Artificial superhydrophobic surfaces that do not absorb water, like the lotus leaf, show tremendous promise in numerous applications. However, superhydrophobic surfaces are rarely used because of their low stability and endurance. A stable organic superhydrophobic surface (SHS) composed of novel morphology Ag-nanoparticles (NPs) has been fabricated on a copper alloy via etching, immersion, spraying, and annealing treatment, along with a static water contact angle (WCA) of 158 ± 1° and sliding angle (SA) less than 2°. The surface texture, composition, and morphology of the substrate surfaces were explored by using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, and DFT-based Ag atom distribution. The anti-corrosion study of non-coated and Ag-NP-coated copper alloy was undertaken using electrochemical impedance spectroscopy. Ag-NPs +SA@SHS enhanced the corrosion resistance as compared with bare Cu alloy. The water droplet rolled down the coated Cu alloy, removed the chalk powder from the surface, and indicated an excellent self-cleaning function. Photodegradation of Congo red (CR) and methylene blue (MB) dye samples was assessed by measuring the absorbance through UV-Visible spectrophotometry, where the Ag-NPs coated on the copper alloy were used as a catalyst. The performance of the SHS@Ag-NPs in the aqueous solution was 99.31% and 98.12% for industrial pollutants (CR and MB), with degradation rates of 5.81 × 10-2 s-1 and 5.89 × 10-2 s-1, respectively. These findings demonstrated a simple, rapid, and low-energy fabrication technique for SHS@Ag-NPs. This research reveals a valuable approach for the fabrication of SHS@Ag-NPs on various substrates to extend the superhydrophobic surfaces with ultra-fast self-healing properties, for outdoor applications such as anti-corrosion, for an innovative approach for the remediation of polluted water treatment, and for industrial applications.

Preparation of a robust and stable superhydrophobic coating with self-cleaning and mold resistance properties on natural bamboo substrate

Bamboo, as an excellent natural material, has received widespread attention and application. However, its defects, including hydrophilicity and poor mold resistance, shorten its service life. Therefore, the best strategy to address the defects of bamboo is to prepare robust and stable superhydrophobic surfaces. This study reports a simple two-step method to prepare superhydrophobic surfaces, using only two materials: rosin and nano-CaCO3. The method is easy to operate, replicable, cost-effective and safe. The prepared superhydrophobic bamboo (SHB) has a water contact angle (WCA) of 153 ± 3°. After being soaked in water at 0 ℃, 20 ℃, 40 ℃, 60 ℃, 80 ℃ and 100 ℃ for 2 h, the WCA of SHB maintained superhydrophobic in a wide range of 0–80 ℃. After being soaked in water at 100 ℃ for 2 h, the WCA of SHB sightly decreased to 147 ± 3°. After 2000 circles of weight friction, the WCA of SHB was 151°. After 1000 circles of tape peeling, the WCA of SHB was 150°. The WCA of SHB was greater than 151 ± 2° after soaked in acidic or alkaline solutions with pH values of 3, 5, 7, 9 and 11 for 2 h. After 6 weeks of fungal culture, the infection rate of SHB was 0%, while the infection rate of clean bamboo (CB) was 100%. In a word, SHB not only has good robustness, chemical stability, high and low temperature resistance, and mold resistance, but also can self-cleaning the dust on superhydrophobic surfaces through liquid droplets.

The effects of carbon ion implantation on wettability, abrasion, thermal and anti-corrosion stabilities of laser ablated super-hydrophobic Nitinol surface

Comparing with pure laser irradiation, the hybrid fabrication using laser ablation and chemical modification is one of the widely used techniques to obtain bio-inspired super-hydrophobic surface. Nevertheless, conventional surface chemical modification techniques have faced challenges including the detachment of micro-nano structures and the instability of super-hydrophobic surfaces. This research introduces an innovative method for creating extremely stable super-hydrophobic surfaces on NiTi alloy through a combination of laser exposure, carbon ion implantation, and modification with fluoroalkylsilane (FAS). Surface morphology and chemical component were systematically investigated to reveal the formation mechanism of super-hydrophobicity. Besides, its abrasion stability, thermal stability and corrosion resistance stability of this kind of super-hydrophobic surface were also investigated. And the corresponding stability improvement mechanisms were further revealed.

Integrated wearable anti-wetting strain sensor with the ability of achieving human joints bending recognition and electricity generation simultaneously

Wearable strain sensor has attracted much attention in human health monitoring, medical rehabilitation, and human-computer interaction. However, it is still a huge challenge for strain sensors to achieve long-term and stable operation in harsh conditions such as exposing to wet environments, directly contacting aqueous solutions or power shortage. Herein, we integrated a wearable, anti-wetting, and self-powered combined-type (WASC) strain sensor consists of three parts: a superhydrophobic and conductive Ti3C2TX (MXene) based composite coating, Ecoflex substrate and a triboelectric nanogenerator (TENG) composed of polyamide and polydimethylsiloxane films. The hierarchical micro/nano mastoid wrinkle structure of the MXene composite coating endowed WASC strain sensor with a wide sensing range (strain over 150%), superior sensitivity (gauge factor of 5678.2), and a stable superhydrophobic surface. Most importantly, the WASC sensor could efficiently monitor real-time human joints bending movements (such as finger bending) and generate electricity simultaneously, without being affected by water, acid, alkali, and salt solution. This described integration strategy of combined-type strain sensor provided a promising method for wearable strain sensors to deal with emergencies such as power shortage, wet environment, or corrosive conditions.

Preparation of 2024-T351 aluminum alloy superhydrophobic surface by laser peening without absorption layer and without confinement layer

The purpose of this study was to investigate the preparation of superhydrophobic surfaces on 2024-T351 aluminum alloy by laser peening without absorption layer and without confinement layer (LPwAC). The wettability, residual stress and microhardness of the treated specimens were measured. The surface morphology of the specimen was characterized by scanning electron microscopy, and the surface elements and crystal orientation were analyzed. The experimental results showed that the micro-nanoporous structure appeared on specimen surface after LPwAC treatment. The superhydrophobic state was observed after chemical modification reduced the surface energy. Additionally, the crystallinity of the surface was increased, the hardness was improved, and residual compressive stress was generated inside the material. LPwAC is an effective process for the preparation of stable 2024-T351 aluminum alloy superhydrophobic surfaces.

Plasmon-Driven Photochemical Reduction Reaction on Silver Nanostructures for Green Fabrication of Superhydrophobic Surface.

Green fabrication of superhydrophobic surface by water-based processing is still challenging, because introduction of the substances with hydrophilic moieties compromises its superhydrophobicity. Herein, a plasmon-driven photochemical reduction reaction under ultraviolet light (UVA) irradiation is first discovered and is applied to deoxygenation of hydrophilic organic adsorbates on rough nano-Ag coating for the formation of stable superhydrophobic surface. A nano-Ag coating with strong localized surface plasmon resonance in the UVA region is prepared by a water-based silver mirror reaction and results in a unique chemical reduction reaction on its surface. Consequently, the low residual hydrophilic functionalities and the formed cross-linked structure of the adsorbate on Ag nanoparticles (NPs) enables the coating to exhibit stable superhydrophobicity against to both air and water. The superhydrophobic Ag NP-coated sandpaper can also be used as a surface-enhanced Raman scattering (SERS) substrate to concentrate aqueous analytes for trace detection.

What if designing superhydrophobic polymer surfaces turned out to be very simple?

Various natural or artificial surface topographies or textures lead to slippery superhydrophobicity, but have little in common. Thus, simple questions need to be asked: what are the key parameters required for reaching slippery superhydrophobicity, i.e. forming a Cassie-Baxter's interface instead of a Wenzel's one? Is the double texturing scale, i.e. nano and micro, imperative to reach this superhydrophobicity regime as usually agreed upon the literature? In this paper, a simple model of the wetting of a textured surface based on the balance between the liquid pressure and the surface tension for a Cassie-Baxter's interface is described. The textured surface is supposed to be slippery superhydrophobic as long as a pure Cassie-Baxter's interface with a contact angle larger than 150° is established. The stability limits of such an interface upon pressure are studied depending on simple parameters such as asperities shape, size, or spacing distance. Then, this model is applied on simple theoretical surfaces and its conclusions are challenged with surface wetting situations described in the literature, showing great accordance. The proposed model offers a simple understanding of the relationship between surface texture and superhydrophobicity. Such an understanding guides the design of stable superhydrophobic surfaces using simple parameters. An ideal surface texture for superhydrophobicity can be described: An intrinsically hydrophobic surface with as small as possible re-entrant asperities that are spaced by more than their own width, and at least as high as their spacing distance.

Superhydrophobic Flexible Silicone Rubber with Stable Performance, Anti-Icing, and Multilevel Rough Structure

Superhydrophobic surfaces made of flexible materials have attracted much attention in the fields of wearable and flexible devices. In this work, an easy-to-process, fluorine-free, mechanically stable superhydrophobic surface with a multilayered rough structure was fabricated by the template/spraying method using silicone rubber with mechanical flexibility, electrical insulation, and bio-inertness. It can form an air layer between the droplet and the sample, reducing the contact area between the droplet and the sample, and its contact angle can reach 170° and the rolling angle can be 2.5°. After many bendings and twistings, the sample still maintains excellent superhydrophobic performance. The contact angle of the sample still exceeded 150° after 100 cm of abrasion on the sandpaper. Droplets can bounce many times on the sample surface without being stuck. Compared with the control surface, the time from the beginning of precooling to the complete freezing of droplets on the superhydrophobic surface was extended by a factor of 3.4 at −10 °C. Therefore, this research still has a bright application prospect in extreme environments.

Fabrication of wear-resistant and superhydrophobic aluminum alloy surface by laser-chemical hybrid methods

To achieve rapid, efficient, and low-cost preparation of large-scale stable aluminum alloy superhydrophobic surfaces, a new preparation method is proposed. The outer surface of the array micro-protrusions was coated with a layer of armor, which was the molten spatter produced during picosecond laser processing. The molten sputters and micro-protrusions combined to form micro–nano composite multi-layer structures. Through these special array micro–nano composite multi-layer structures and chemical modification, the wear-resistant and superhydrophobic properties of aluminum alloy surfaces were realized. According to test results, the array micro–nano composite structures prepared by picosecond laser and chemical modification had a water drop contact angle of 154.6° and a water drop rolling angle of 2°, exhibiting excellent superhydrophobic and anti-adhesion properties. Its self-cleaning, corrosion resistance and friction and wear behavior were systematically analyzed. The analysis results showed that the rolling droplets on the prepared surface could easily take away contaminants. The corrosion voltage and corrosion current density of the prepared superhydrophobic surface are significantly lower than that of the raw surface. In addition, a water drop contact angle of the aluminum alloy sample maintained at 145.1° after five wear tests, indicating the prepared surface after wear testing still had hydrophobic performance. The innovative method proposed in this study provides a simple and effective method for preparing large-scale wear-resistant superhydrophobic surface of aluminum alloy.

Study on Hydrophobic Surface of Magnesium Alloy Prepared by Femtosecond Laser and its Corrosion Resistance

Due to their excellent barrier and shielding effects, superhydrophobic magnesium alloy surfaces are increasingly interested in corrosion protection. This paper proposes a method for producing a stable superhydrophobic surface by laser scanning ablation of AZ31B magnesium alloy on its surface. The prepared layered micro-nanoemulsion convex structure with a lotus-like surface exhibited excellent superhydrophobicity after modification by stearic acid, and the static water droplet contact angle reached 163°. After 90 days in outdoor air, droplet pressure-based experiments show that the superhydrophobic surface possesses a long-term stable Cassie state. In addition, The superhydrophobic surface showed excellent corrosion resistance against magnesium alloy in a Neutral 3.5 wt.% NaCl solution. The results of the dynamic potential polarization tests showed that the existence of a gas layer cavity on the lotus-like surface structure caused the corrosion current density of superhydrophobic AZ31B (3.86±1 uA/cm2) to decrease by 2 orders of magnitude compared with that of the extruded AZ31B (103±1 uA/cm2). We believe the proposed method is simple, efficient, and non-polluting, especially for medical magnesium alloys in the field of in vivo implant materials to slow down corrosion and promote clinical applications.

Biochar based self cleaning superhydrophobic surface with aqueous DESphobic properties

In this work, facile fabrication of chemically stable superhydrophobic surfaces based on biocompatible, fluorine free, carbon rich biochar has been reported. Biochar synthesized from dried rice straw by pyrolysis at 550˚C, which was characterized using Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM). The biochar coated surface demonstrated superhydrophobic behaviour with static water CA > 150°. Aqueous drops remain in superhydrophobic state due to stability of Cassie-Baxter wetting regime and can shows very high-water contact angle (WCA > 160°) and self-cleaning behaviour. Such a very high WCA have been achieved typically by combination of low energy chemicals (fluorine based) and surface textures. However, no harsh chemical treatment of biochar was performed and a simple methodology of creating biochar layer onto the substate was adopted. Such surface also demonstrated repellent properties against aqueous mixtures of deep eutectic solvent (DES). A spherical aqueous DES drop can be easily formed onto the biochar surface for image analysis. The density of the liquid sample with a small sample volume can be assessed using this drop shape that was measured on the superhydrophobic biochar surface.

An underwater stable superhydrophobic surface for robust ultra-long-lasting biofouling resistance

An underwater stable superhydrophobic surface that displays a very low affinity to water and microorganisms is urgently required in marine engineering and offshore constructions. In this study, we demonstrated an underwater stable superhydrophobic surface with pressure resistance, chemical stability, biocompatibility, and biofouling resistance. The surface demonstrated superhydrophobicity under a water pressure of 13.72 kPa for up to 27 days. To examine the anti-biofouling property of the surface, the as-prepared samples were submerged in a natural lake for 50 days. The surface could withstand water flush and biological attacks for more than 35 days. The mechanical stability of the surface was evaluated by a sandpaper scratching test. An abrasion length of 12 m would not decrease the water contact angle of the surface, which is superior over the state-of-the-art coatings based on candle soot networks. The stable long-lasting underwater superhydrophobic surface is of great importance to marine applications.

Recent Advances on the Abrasion Resistance Enhancements and Applications of Superhydrophobic Materials.

Researches on superhydrophobicity have been overwhelming and have shown great advantages in various fields. However, the abrasion resistance of superhydrophobic structures was usually poor, and they were easily damaged by external force or harsh environment, which greatly limited the applications of superhydrophobic surfaces. Much attention has been paid to improving the abrasion resistance of superhydrophobic materials by researchers. In this review, aimed at the advances on improving the abrasion resistance of superhydrophobic surfaces, it was summarized and compared three enhancement strategies including the reasonably design of micro-nano structures, the adoption of adhesives, and the preparation of self-healing surface. Finally, the applications of typical superhydrophobic materials with abrasion resistance were reviewed in various fields. In order to broaden the application fields of superhydrophobic materials, the abarasion resistance should be further improved. Therefore, we proposed the ideas for the future development of superhydrophobic materials with higher abrasion resistance. We hope that this review will provide a new approach to the preparation and development of stable superhydrophobic surfaces with higher abrasion resistance.

Stable and drag-reducing superhydrophobic silica glass microchannel prepared by femtosecond laser processing: Design, fabrication, and properties

The superhydrophobic silica glass microchannel with flow drag reduction performance has broad application prospects. In response to this demand, this paper proposes an integrated design and preparation method of structure and function for drag reduction microchannels on the silica glass surface. The design method of geometric parameters of stable superhydrophobic silica glass surface structures with a periodic micropillar array is studied based on the drag reduction mechanism of superhydrophobic surfaces. Combined with the plasma deposition process, the drag-reducing superhydrophobic silica glass surface is successfully prepared by femtosecond laser technology. The prepared drag-reducing superhydrophobic silica glass surface shows good composite wetting state stability under different test conditions. The drag-reducing superhydrophobic functional structure with a micropillar array is prepared at the bottom of the silica glass microchannels by femtosecond laser direct writing technology. Moreover, the effective integration of the silica glass microchannel structure and the drag-reducing functional structure is achieved. The preparation and flow performance test of microfluidic devices demonstrates that drag-reduction microchannels of silica glass can significantly reduce microfluidic flow resistance. The proposed method effectively improves the functional characteristics of ultrafast laser processing surface microchannels in silica glass and has broad application prospects in fluid flow and control.

An extremely efficiency method to achieve stable superhydrophobicity on the surface of additive manufactured NiTi Alloys: “Ultrasonic Fluorination”

The realization of superhydrophobic helps to enhance the anti-corrosion, self-cleaning and other properties of the material surface. Compared with polymer materials, metallic have superior strength, hardness and stability in superhydrophobicity. For most metals, the standard superhydrophobic treatment method is a combination of micro-nano hierarchical structure and low surface energy modification Herein, SLM-NiTi with broad application prospects in biomedical and engineering fields is selected for the first time. The nanosecond laser processing method was used to construct the surface with the micro-nano hierarchical structure, and a new low surface energy modification method (ultrasonic fluorination) was innovatively proposed. Ultimately, a stable superhydrophobic surface of SLM-NiTi was successfully achieved. The results show that ultrasonic fluorination treatment can achieve surface modification in only 10 min, which is far more efficient than other low surface energy treatment methods. Simultaneously, it is found that the realization of superhydrophobicity of metallic surfaces depends on the nanosecond laser process parameters. Moreover, the frictional stability and durability of the surfaces are also demonstrated, which inspired new applications in extreme environments. We envision this work not just for SLM-NiTi alloys but for broadly applicable in various metals, dramatically improving the period for realizing superhydrophobic functions on metallic surfaces.

A new superhydrophobic polypropylene hollow fiber membrane preparation method and its application in the treatment of brine with high salt concentration

A simple and effective strategy combining etching, electrostatic adsorption, and dip-coating methods was developed in this paper to prepare uniform and stable superhydrophobic surfaces on polypropylene hollow fiber membranes (PPHFM) for desalination of highly concentrated salt solutions (3.5 wt% − 15 wt%). A number of appropriate evaluation methods were used to characterize the membrane, and the results confirmed that the composite membrane was successfully modified. Compared with PPHFM, the water contact angle (WCA) was increased from 119° to 165°; the surface roughness was increased from 0.198 µm to 0.961 µm; the mean pore size was increased from 0.16 µm to 0.24 µm; the porosity was increased from 53% to 70%. The PPHFM and composite membranes were applied to a long-term (80 h) vacuum membrane distillation (VMD) with a salt concentration of 15 wt%. The average permeates flux of the composite membrane increased from 4.27 kg (m2 h)−1 to 12.33 kg (m2 h)−1 compared to the PPHFM, while the composite membrane had superior resistance to wetting and stability.