Bio-inspired Superhydrophobic Surfaces Research Articles

Boosting corrosion resistance of Mg-Li alloy: Implanting bioinspired superhydrophobic surfaces into MAO matrix for enhanced protection

The corrosion problem has significantly impeded the practical application of Mg-Li alloys. In this report, a method that combines micro-arc oxidation (MAO) with electrochemical deposition is developed to create a superhydrophobic matrix on Mg-Li substrate. The combination approach harnesses the superiority of both coverages, including MAO as the dense, firmly bonded ceramic oxide layer on the metal substrate and the superhydrophobic surface (SHS) implanted into MAO matrix. The MAO-SHS coating exhibits high mechanical stability, maintaining the superhydrophobicity due to the “implanting effect” even after a long distance of friction effect. For corrosion inhibition, compared to the bare Mg-Li with icorr of 9.26 × 10−5 A/cm2, the icorr for MAO and MAO-SHS is 7.83 × 10−6 A/cm2 and 7.50 × 10−9 A/cm2, respectively, representing the reduction of approximately one and four orders of magnitude. Focusing the atmospheric corrosion inhibition, MAO-SHS proves to manipulate the dynamic evolution of saline solution evaporation and salt particle deliquation. The salt particle crystalized from saline solution on MAO-SHS is found to have significantly smaller contact area than that of the bare Mg-Li and MAO. By employing atomic force microscopy, the adhesion force of salt particle is revealed as ca. 45 nN, 13 nN, and 2 nN for salt particle on Mg-Li, MAO, and MAO-SHS, respectively. This suggests that the salt can be more easily removed from the MAO-SHS surface, thereby reducing the susceptibility to corrosion. The in situ deliquation is conducted to understand the formation of the droplet on different surfaces. The air in the SHS layer hinders chloride ingress and the SHS layer seals the pores in MAO layer, proving the synergistic effect afforded by MAO-SHS to achieve superior corrosion resistance.

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.

The Relationship between Nanostructured Bio-Inspired Material Surfaces and the Free Energy Barrier Using Coarse-Grained Molecular Dynamics.

Bio-inspired (biomimetic) materials, which are inspired by living organisms, offer exciting opportunities for the development of advanced functionalities. Among them, bio-inspired superhydrophobic surfaces have attracted considerable interest due to their potential applications in self-cleaning surfaces and reducing fluid resistance. Although the mechanism of superhydrophobicity is understood to be the free energy barrier between the Cassie and Wenzel states, the solid-surface technology to control the free energy barrier is still unclear. Therefore, previous studies have fabricated solid surfaces with desired properties through trial and error by measuring contact angles. In contrast, our study directly evaluates the free energy barrier using molecular simulations and attempts to relate it to solid-surface parameters. Through a series of simulations, we explore the behavior of water droplets on surfaces with varying values of surface pillar spacing and surface pillar height. The results show that the free energy barrier increases significantly as the pillar spacing decreases and/or as the pillar height increases. Our study goes beyond traditional approaches by exploring the relationship between free energy barriers, surface parameters, and hydrophobicity, providing a more direct and quantified method to evaluate surface hydrophobicity. This knowledge contributes significantly to material design by providing valuable insights into the relationship between surface parameters, free energy barriers, and hydrophilicity/hydrophobicity.

Advances in Bioinspired Superhydrophobic Surfaces Made from Silicones: Fabrication and Application.

As research on superhydrophobic materials inspired by the self-cleaning and water-repellent properties of plants and animals in nature continues, the superhydrophobic preparation methods and the applications of superhydrophobic surfaces are widely reported. Silicones are preferred for the preparation of superhydrophobic materials because of their inherent hydrophobicity and strong processing ability. In the preparation of superhydrophobic materials, silicones can both form micro-/nano-structures with dehydration condensation and reduce the surface energy of the material surface because of their intrinsic hydrophobicity. The superhydrophobic layers of silicone substrates are characterized by simple and fast reactions, high-temperature resistance, UV resistance, and anti-aging. Although silicone superhydrophobic materials have the disadvantages of relatively low mechanical stability, this can be improved by the rational design of the material structure. Herein, we summarize the superhydrophobic surfaces made from silicone substrates, including the cross-linking processes of silicones through dehydration condensation and hydrosilation, and the surface hydrophobic modification by grafting hydrophobic silicones. The applications of silicone-based superhydrophobic surfaces have been introduced such as self-cleaning, corrosion resistance, oil-water separation, etc. This review article should provide an overview to the bioinspired superhydrophobic surfaces of silicone-based materials, and serve as inspiration for the development of polymer interfaces and colloid science.

Biomimetic slippery liquid-infused porous surface on the basis of hierarchical ZIF-67@Cu dendrite: Preparation and corrosion inhibition

In the harsh environment, the corrosion of Cu leads to the failure of pipelines, condenser, printed circuit board and so forth. Thus, protecting Cu from corrosion is critically important from both science and engineering backgrounds. In this report, the hierarchical structure compositing dendritic Cu and ZIF-67 is prepared onto Cu by a two-step electrodeposition protocol. After thiol modification and oil infusion, bio-inspired superhydrophobic surface (SHS) and slippery liquid-infused porous surface (SLIPS) is respectively achieved, and sophisticated techniques are used for characterizing chemical composition, morphology, topology and wettability. Scanning Kelvin probe is employed to know the surface potential distribution before and after the biomimetic transformation. Using different electrochemical approaches, the corrosion inhibition effect is elucidated. In 3.5 wt% NaCl corrosive medium, |Z|0.01Hz of SLIPS is as high as 1.35 × 108 Ω·cm2 at the initial immersion stage. The value is remarkably enhanced compared with SHS (6.76 × 104 Ω·cm2) and bare Cu (8.74 × 103 Ω·cm2). After soaking for 168 h, |Z|0.01Hz value of SHS and SLIPS is 3.84 × 104 Ω·cm2 and 4.93 × 106 Ω·cm2, illustrating that SLIPS has high resistance to protect Cu from corrosion.

Fabrication of a superhydrophobic micron-nanoscale hierarchical structured surface for delayed icing and reduced frosting

Multifunctional superhydrophobic surfaces with dual-scale hierarchical structures have drawn considerable interest in real-world applications. The complicated fabricating process, higher costs, and poor durability limit the widespread utilization of bio-inspired superhydrophobic surfaces. Herein, we use an effective method to create a micron-nanoscale (dual-scale) hierarchical structure, which is composed of a micron-scaled rough structure constructed by a chemical-etching process and a secondary nanostructure obtained by hydrophobic nano silica (SiO2) modification. The micron-nanoscale hierarchical structured surface has superhydrophobicity with a water contact angle of 161.5°±1.9°. Compared with the micron-scaled rough structure surface, the manufactured micron-nanoscale hierarchical structured surface presented excellent anti-icing properties with a freezing delay time of 5013.6 s at -15 °C. The frost layer on the micron-nanoscale hierarchical structured surface can be rapidly melted to transform into some isolated water droplets in about 7 s due to its ultra-low water adhesion force. Additionally, the prepared superhydrophobic micron-nanoscale hierarchical structured surface has chemical stability and mechanical durability except for the delayed icing and reduced frosting performance. The construction of a micron-nanoscale hierarchical structure is expected to expand superhydrophobic surface applications in anti-icing, anti-frosting, and self-cleaning.

Electrochemical polishing assisted selective laser melting of biomimetic superhydrophobic metallic parts

Metallic superhydrophobic surfaces can be widely used in pipeline transportation, oil–water separation, anti-icing, biomedicine and industrial production owing to their excellent properties. The biologically non-smooth superhydrophobic structure provides a biomimetic prototype for superhydrophobic metal surface processing. However, processing micro-nano biomimetic structures on the internal surface of complex pipelines is difficult because of the limitations of traditional molding processes. Herein, a superhydrophobic butterfly wing is imitated via the selective laser melting technology to print a pit prototype on the surface during the complex parts forming, and then the bio-inspired superhydrophobic internal surface of the 316L stainless steel is successfully prepared by the processes of electrochemical polishing, chemical etching, fluorosilane modification, and low temperature drying, sequentially. The morphology, wettability, corrosion resistance, and elemental composition of the obtained surface are characterized. The results show that a uniform pit-shaped micro-nano composite structure is formed on the surface, the contact angle is up to 155°, the rolling angle is less than 10°, and the corrosion resistance is significantly improved. Finally, a complex superhydrophobic inner surface square tube with application value is successfully prepared, and its excellent superhydrophobicity and self-cleaning properties are verified. This fabrication method provides an idea for the complication of metal superhydrophobic structures, and will promote the application of additive manufacturing in the engineering field.

Bioinspired superhydrophobic surface via one-step electrodeposition and its corrosion inhibition for Mg-Li alloy

The extremely low corrosion resistance of Mg-Li alloy is a critical obstacle to overcome for its practical usage. In this work, targeting this hard problem, we prepare bioinspired superhydrophobic surface onto Mg-Li (LA141) alloy (contact angle up to 167.4° with the sliding angle as low as 1°) for corrosion prohibition by a facile one-step electrodeposition. Transient image capture technique reveals the dynamic interaction between water droplet and superhydrophobic surface, demonstrating the strong repellency to water phase. Superhydrophobic surface plays an essential role in limiting the time of wetness, so that the opportunity for corrosion will be substantially decreased. In atmospheric condition, the corrosion inhibition capability of superhydrophobic coating to Mg-Li alloy is revealed by scanning Kelvin probe. In water immersion state, the electrochemical impedance spectroscopy and the potentiodynamic polarization curve technique is used to uncover the corrosion resistance of the superhydrophobic coatings prepared under different voltage and time. The electrochemical impedance obtained at 40 V after electrolysis for 30 min is up to 5.62 × 105 Ω cm2, which is about 104 times larger than that of the bare state Mg-Li alloy. Meanwhile, the corrosion current density is about 4.36 × 10−8 A/cm2, which is ca. 4 orders of magnitude lower than that of bare Mg-Li alloy, suggesting great corrosion resistance property of the prepared coating in this work.

Investigations of interfacial heat transfer and phase change on bioinspired superhydrophobic surface for anti-icing/de-icing

The bioinspired superhydrophobic surface (SHS) demonstrates the capability in terms of anti-icing/de-icing, however, the mechanisms of micro−/nanostructure on interfacial heat transfer and phase change are inadequately revealed during freezing. A comprehensive solution method, considers a modified roughness, texture, and thermal properties of SHSs material, is developed in this study. This method, coupled Level Set-Volume of Fluid (CLSVOF) with solidification model and combined freezing experiments, captures the ice-liquid-gas interface change and anisotropic interfacial heat exchange. Numerical and experimental results in frozen nucleation illustrate that the micro−/nanostructure blocks heterogeneous heat transfer via the stored air, extended the freezing time and the freezing delay rate is 194%. Accordingly, the numerical model between freezing time (t) and surface temperature (Tsurface), is following power function t = 959.42 × (273.15 − Tsurface)−0.777. Moreover, the moving droplets overcome the freezing adhesion through shortening the contact time then to limit the heat exchange process, allowing their self-removal before freezing. The de-icing analysis confirms that the larger contact angle (CA) and cavitation structure jointly affect the solid-liquid contact area, and the bionic surface in this study reduces the adhesion strength of frozen droplets by 4 times.

Recent advances in bioinspired superhydrophobic ice-proof surfaces: challenges and prospects.

Bionic superhydrophobic ice-proof surfaces inspired by natural biology show great potential in daily life. They have attracted wide research interest due to their promising and wide applications in offshore equipment, transportation, power transmission, communication, energy, etc. The flourishing development of superhydrophobic ice-proof surfaces has been witnessed due to the availability of various fabrication methods. These surfaces can effectively inhibit the accumulation of ice, thereby ensuring the safety of human life and property. This review highlights the latest advances in bio-inspired superhydrophobic ice-proof materials. Firstly, several familiar cold-resistant creatures with well-organized texture structures are listed briefly, which provide an excellent template for the design of bioinspired ice-proof surfaces. Next, the advantages and disadvantages of the current techniques for the preparation of superhydrophobic ice-proof surfaces are also analyzed in depth. Subsequently, the theoretical knowledge on icing formation and three passive ice-proof strategies are introduced in detail. Afterward, the recent progress in improving the durability of ice-proof surfaces is emphasized. Finally, the remaining challenges and promising breakthroughs in this field are briefly discussed.

Investigations of Interfacial Heat Transfer and Droplet Nucleation on Bioinspired Superhydrophobic Surface for Anti-Icing/De-Icing

Investigations of Interfacial Heat Transfer and Droplet Nucleation on Bioinspired Superhydrophobic Surface for Anti-Icing/De-Icing

Femtosecond laser micro/nano fabrication for bioinspired superhydrophobic or underwater superoleophobic surfaces

Femtosecond laser micro/nano fabrication for bioinspired superhydrophobic or underwater superoleophobic surfaces

Anisotropic Superhydrophobic Properties of Bioinspired Surfaces by Laser Ablation of Metal Substrate inside Water (Adv. Mater. Interfaces 16/2021)

Bioinspired Superhydrophobic Surface A novel bioinspired surface with tilt wedge-shaped structures is fabricated on the aluminum substrate by nanosecond laser ablation inside water, as presented in article number 2100555 by Xuyan Hou, Minghui Hong, and co-workers. The theoretical model is established to explain the anisotropic phenomenon on the bioinspired surface. The bouncing and rolling movements of water droplets on the surface are simulated and tested to explain the anisotropic phenomena on the wedge-shaped structures at different tilt angles.

Researching Advances in Application of Bio-Inspired Superhydrophobic Metallic Surface

Metal materials are very important engineering materials, which are irreplaceable in the history of mankind. Infiltrating theoretical basis described in the paper comprehensively introduces the super hydrophobic of metal surface which has important theoretical significance and broad application prospects in many fields of basic research and industrial application including self-cleaning, fluid drag reduction, water miniature conveyer, condensation, ice prevention, resistant corrosion and protection, liquid transmission, oil-water separation, biological fouling and Marine fouling and control, etc. It also puts forward the corrosion mechanism of super hydrophobic surface to extend the bionic super hydrophobic metal materials in the field of industrial and civilian sectors.

Chemical Fabrication Strategies for Achieving Bioinspired Superhydrophobic Surfaces with Micro and Nanostructures: A Review

Biological surfaces in nature, such as lotus leaves, rose petals, and water striders, exhibit excellent superhydrophobicity. The fabrication of superhydrophobic surfaces inspired by nature has become an important research topic. The potential application of superhydrophobic surfaces in many fields has promoted the rapid development of fabrication techniques. Various chemical methods, such as chemical vapor deposition techniques, solution immersion methods, electrochemical techniques, hydrothermal method, and sol–gel process, have been proposed for fabricating superhydrophobic surfaces due to their low cost, simple preparation, and easy promotion. Herein, the progress of chemical fabrication methods of superhydrophobic surfaces in recent years is focused on and the strengths and weaknesses of each technique are analyzed. At last, a brief conclusion of the challenges and perspectives on the fabrication of superhydrophobic surfaces is provided.

Bio-inspired Superhydrophobic Self-healing Surfaces with Synergistic Anticorrosion Performance

The past decade has witnessed significant efforts in addressing the global metallic corrosion challenge, with a focus on avoiding or mitigating huge economic losses incurred by corrosion and on the development of protective coatings on metals. Herein, a synergistic anticorrosion coating with both superhydrophobicity and self-healing properties was reported, through a facile replica molding method by mixing the polyvinylidene fluoride (PVDF) matrix with nano-sized SiO2 particles and 2-mercaptobenzothiazole (MBT) loaded halloysites (HNTs). The surface exhibits robust self-cleaning behavior under harsh conditions and high liquid repellence to withstand the osmosis of corrosive ions. The self-healing performance of the coating, due to the introduction of MBT-loaded HNTs, enhances the anticorrosion capability, which is still valid once the protective layer is damaged. Potentiodynamic polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) measurements demonstrate that the synergetic effects in anticorrosion performances significantly enhance the long-term corrosion protection of metals. Hence, this type of dual-action coating may find unique applications in metal corrosion resistance where both super-repellency and self-healing properties are desired.

Fabrication of superhydrophobic surfaces inspired by “stomata effect” of plant leaves via swelling-vesiculating-cracking method

Fabrication of superhydrophobic surfaces by simple techniques is of significant interest. Herein, inspired by the “stomata effect” of plant leaves, a superhydrophobic surface with bionic stomata randomly on polydimethylsiloxane (PDMS) is fabricated by a facile swelling-vesiculating-cracking method. Neither multistep modification of nanostructure nor introduction of low surface energy substance is carried out during the fabrication. The water contact angle (CA) of the bio-inspired superhydrophobic surfaces with stomata-like structures (BSSS) can reach 168.4 ± 1° with 8.9° sliding angle and less than 10° contact angle hysteresis (CAH). The structure and wettability of the BSSS are characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive spectrometry and X-ray photoelectron spectroscopy. The effects of swelling ratio, heat treatment temperature and surface morphology on the hydrophobicity of the BSSS are investigated systematically. Noticeably, the BSSS are provided with wonderful durability in organic solvents, ice water, and strong acid solution. Furthermore, a theoretical model for BSSS based on the Cassie-Baxter relation is established to elucidate the “stomata effect”. The model reveals that the water contact angle will reach 180° when the stomata-like structure is suitable. The fabrication of BSSS provides a potential strategy for the development of novel superhydrophobic materials.

The investigation of mechanical and thermal properties of super-hydrophobic nitinol surfaces fabricated by hybrid methods of laser irradiation and carbon ion implantation

Comparing with laser irradiation only, the laser ablation combined with chemical modification process is a widely used technique to obtain bio-inspired super-hydrophobic surface. However, the as-prepared surfaces may be polluted by toxic substance during chemical modification such as fluoroalkyl silane and stearic acid. The side effect of polluted functional surface on organisms and environment limited its application value. In this paper, a green and environmental-friendly super-hydrophobic surface was quickly fabricated on nitinol substrates through hybrid of nanosecond laser ablation and carbon ion implantation. The time that turning from super-hydrophilicity to super-hydrophobicity was only 16 h exhibiting high efficiency compared with pure laser processing. Surface morphology and chemical component were systematically investigated to reveal the formation mechanism of super-hydrophobicity in such short time. The mechanical abrasion tests implied that the mechanical properties of surface microstructure could be heightened after carbon ion implantation, showing the superior structure stability. It is noted that chemical modified super-hydrophobicity could be hardly destroyed under high temperature, and the thermal stability of this ion implanted super-hydrophobic surface was on a par with it. This hybrid method of laser irradiation and carbon ion implantation paves a green way for rapid fabrication super-hydrophobic surface on nitinol, which would have great application value in biomedicine and industry.

Cross-Linked Organic-Inorganic Hybrid Composite Films for One-Step Fabrication of Robust Superhydrophobic Surfaces.

Despite the recent demands of bioinspired superhydrophobic surfaces with self-cleaning properties in various industrial applications, a low-cost fabrication method for superhydrophobic films with excellent stability has rarely been studied. Herein, we report a robust superhydrophobic organic- inorganic hybrid composites film produced via a facile one-step solution-process. As coating materials for the facile one-step fabrication of the robust superhydrophobic films, we included Al₂O₃ nanoparticles for micro/nano hierarchical dual-scale structures, alkylsilane for low surface energy, and organic cross-linkers for increasing the stability of the hybrid composite films. Based on the hydrophobicity and stability tests of the hybrid composite films, the optimized composition of the robust superhydrophobic hybrid composite films showed high water contact angles (>150°) and low sliding angles (<5°) as well as excellent mechanical and thermal stability (up to 350 °C).

Constructing Mechanochemical Durable and Self-Healing Superhydrophobic Surfaces.

Bioinspired superhydrophobic surfaces have attracted great interest due to their special functions and wide applications. However, it is still a big challenge to construct a durable superhydrophobic coating for large-scale applications due to its easy destruction by the mechanochemical attack. In this mini-review, we present the state-of-the-art developments in the rational design of mechanochemical durable and self-healing superhydrophobic surfaces. First, the mechanically durable superhydrophobic surfaces are constructed to endure mechanical damage by adjusting the surface morphology and increasing the binding force between the substrates and the modified materials. Second, chemical damages also have been taken into consideration to develop chemically robust superhydrophobic surfaces, such as chemical etching, ultraviolet (UV)-light irradiation, and bioerosion, etc. Third, endowing superhydrophobic coatings with self-healing function can effectively improve the durability and prolong the lifespan of the coatings by releasing low-surface-energy agents or regenerating topographic structures. Finally, the challenges and future perspectives in developing super durable bioinspired superhydrophobic surfaces by structure design and chemistry control are discussed. The innovative points provided in this mini-review will provide deep fundamental insight for prolonging the lifetime of the superhydrophobic surfaces and enable their practical applications in the near future.