Robust Surfaces Research Articles

Eco-friendly synthesis of robust bioinspired cotton fabric with hybrid wettability for integrated water harvesting and water purification

The super-wettability surfaces have attracted tremendous attention as multifunctional materials for the increasing shortage of water resources. Although the bioinspired patterned superhydrophobic-hydrophilic surfaces have been used for water collection, its practical applications are seriously restricted by the complicated or pollution-carrying fabrication methods, the poor durability, and the specific application. It is highly desirable to synthesize the versatile robust surfaces with special wettability for synergistic water harvesting and water purification. In this work, the “one-for-all” robust cotton fabric with hybrid wettability for integrated water harvesting and water purification was prepared by the facile, non-fluorinated, and eco-friendly method. The performance of durability, oil/water separation, self-cleaning and antibacterial of superhydrophobic cotton fabric (SHC) was investigated. Experiment results indicated that the unique three-dimensional (3D) isotropic structure and extraordinary intrinsic properties of tetrapod-shaped ZnO (T-ZnO) enhanced the comprehensive performance of SHC as compared to those incorporated with conventional fillers. The excellent antibacterial activities against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were still retained even after serious mechanical damage. Moreover, the superhydrophobic-hydrophilic patterned cotton fabrics were achieved after SHC covering with different masks under UV irradiation. By regulating the droplet coalescence and transportation during water harvesting, the as-prepared patterned fabric exhibited the enhanced water collection rate (WCR) up to 208.3 mg cm−2·h−1, which was 3 times higher than that of the superhydrophilic or superhydrophobic cotton fabrics. Therefore, this simple strategy to achieve cotton fabric with hybrid wettability shows a promising application in integrated water treatment.

Preparation of Stable Superhydrophobic Coatings on Complex‐Shaped Substrates

AbstractSuperhydrophobic surfaces have potential applications in many fields, but are seriously hindered by their complicated preparation methods and low mechanical stability. Thus, novel strategies for efficient preparation of robust superhydrophobic surfaces on various substrates are highly desired. Here, the preparation of stable superhydrophobic coatings on complex‐shaped substrates by the combination of phase separation and dip‐coating is reported. The coatings show excellent superhydrophobicity for both water and other frequently used liquids, superior impalement resistance, and high stability. Moreover, this strategy can make diverse complex‐shaped substrates superhydrophobic, outperforming the conventional methods. The strategy also has many other merits such as simple, fast (<1 min), scalable (50 kg stock solution per batch and large superhydrophobic samples), and low cost (7.8 CNY m−2 or 1.2 UDS m−2). The superhydrophobic coatings may find applications in many fields including anticorrosion and antiicing, and the findings here will inspire straightforward preparation of robust superhydrophobic coatings on diverse substrates.

A potential method to induce hydrophobicity on glass surface while retaining its anti-reflective abilities

Fabrication of anti-reflective and hydrophobic glass surfaces has been an active area of research. It has been reported that most of the coatings developing methods produces fragile and thin coatings which consequently have limited practical usage because of their abrasion-sensitivity. However, with thicker coatings, transparency of glass gets compromised, rendering it inoperable to be used in applications requiring transparency. To overcome the problem there is a need to have a solution that can practically produce glass substrates having hydrophobic properties without significant loss in transmittance, making them useful in anti-reflective hydrophobic applications. The presented work focuses on utilizing the effects of surface roughness and surface chemistry on commercial grade glass substrates to produce robust hydrophobic surfaces without appreciable compromise on transmittance. Metal Assisted Chemical Etching (MACE) was used to develop controlled structured surface roughness on the glass substrate whereas the surface chemistry was modified via silane treatment. The results demonstrated surface roughness and surface chemistry are both equivalently important to achieve an optimum surface having hydrophobic properties without any major transmittance lost. Successful implementation of the silver (Ag) particle assisted MACE process and chemistry modification of the glass surface resulted in contact angles above 100° with nearly 2–3% transmission lost in reference to the transmittance of parent glass substrates.

Facile Fabrication of Highly Hydrophobic Onion-like Candle Soot-Coated Mesh for Durable Oil/Water Separation.

Although sundry superhydrophobic filtrating materials have been extensively exploited for remediating water pollution arising from frequent oil spills and oily wastewater emission, the expensive reagents, rigorous reaction conditions, and poor durability severely restrict their water purification performance in practical applications. Herein, we present a facile and cost-effective method to fabricate highly hydrophobic onion-like candle soot (CS)-coated mesh for versatile oil/water separation with excellent reusability and durability. Benefiting from a superglue acting as a binder, the sub-micron CS coating composed of interconnected and intrinsic hydrophobic carbon nanoparticles stably anchors on the surface of porous substrates, which enables the mesh to be highly hydrophobic (146.8 ± 0.5°)/superoleophilic and resist the harsh environmental conditions, including acid, alkali, and salt solutions, and even ultrasonic wear. The as-prepared mesh can efficiently separate light or heavy oil/water mixtures with high separation efficiency (>99.95%), among which all the water content in filtrates is below 75 ppm. Besides, such mesh retains excellent separation performance and high hydrophobicity even after 20 cyclic tests, demonstrating its superior reusability and durability. Overall, this work not only makes the CS-coated mesh promising for durable oil/water separation, but also develops an eco-friendly approach to construct robust superhydrophobic surfaces.

Preparation of fluorine- and nanoparticle-free superwetting polybenzoxazine/cellulose composites for efficient oil/water separations

Considering the dangers of spilled oil, it is important to develop economical materials for the rapid removal of oil contaminants. Herein, we report the successful synthesis of a furan-based polybenzoxazine (Fu-PBZ) and present an easy method for preparing robust superhydrophobic surfaces on a cotton fabric and filter paper, using a non-solvent-induced phase inversion method. The cured Fu-PBZ possessed unusual flexibility, low surface free energy (as low as 13.5 mJ m−2), and an extremely high glass transition temperature. The Fu-PBZ-modified cotton fabric (Fu-PBZ@CF) and Fu-PBZ-modified filter paper (Fu-PBZ@FP) both possessed superhydrophobicity and superoleophilicity. Fu-PBZ@CF exhibited excellent separation performance for versatile oil/water mixtures with permeation fluxes of up to 116,000 L m−2 h−1 and efficiency greater than 98%. Fu-PBZ@FP exhibited a permeation flux of up to 5010 L m−2 h−1 and oil purity greater than 99.96% in separating the surfactant-stabilized water-in-oil emulsions. The low surface free energy and hydrophobicity of the binder polymer provided by the self-roughness of the Fu-PBZ coating assisted the substrates in recovering their superhydrophobic property even after repeated applications, rendering our modified materials a viable candidate for practical applications.

Functionally Integrated Device with Robust and Durable Superhydrophobic Surface for Efficient, Continuous, and Recyclable Oil–Water Separation

AbstractA cost‐efficient, universal adhesive layer‐involved strategy is demonstrated for the construction of robust superhydrophobic surfaces on a variety of materials. This strategy uses recycled rubber particles (RRPs) and low‐surface‐energy coating to generate superhydrophobicity, which are fixed on the substrates by a precoated E‐44 resin (ER) adhesive layer. Benefitting from the robust ER adhesive layer and wear‐resistant rubber particles, the ER/RRPs composite coated low‐surface‐energy coating (ER/RRPs/LSEC composite) shows high robustness under various harsh conditions including repeated abrasion, sunlight radiation, and acid/basic corrosion. When evaluated as functionally integrated device for oil spill cleanup, these superhydrophobic structures show excellent oil‐absorption and oil–water separation properties. For example, the copper foam device coated with the ER/RRPs/LSEC composite shows a high oil–water separating efficiency of 95% before and after mechanical abrasion. This strategy provides a new toolbox for constructing robust superhydrophobic surfaces with oil–water separation applications and offers a novel insight into the durability of artificial superhydrophobic surfaces.

Resilient moth-eye nanoimprinted antireflective and self-cleaning TiO2 sputter-coated PMMA films

Moth-eye nanostructures are amongst the most remarkable surfaces in nature because of their multi-functionality including antireflection, self-cleaning and bactericidal ability. Moth-eye surfaces consist of subwavelength arrays of tapered nanostructures, which are challenging to reproduce artificially. Nanoimprint lithography is probably one of the most suited technologies for this purpose. However, the poor mechanical resilience and durability of the polymeric nanocones when exposed to the environment, hinders their use in actual applications. To overcome these limitations, this work demonstrates the use of a thin oxide coating over the polymer moth-eye features imprinted on poly methyl methacrylate (PMMA) films. Particularly TiO2 conformal thin film coatings are deposited by unipolar pulsed dc magnetron sputtering over the antireflective nanopatterns acting as encapsulant. The coating, while preserving the antireflective properties, protects the nanostructures against mechanical scratching and improves substantially their thermal stability to over 250 °C. Furthermore, the TiO2 layer provides additional photoinduced self-cleaning functionality and at the same time it protects the matrix from UV photodegradation. The robust and durable antireflective surfaces developed here may find application on solar cells covers, flat panel displays or on optical components.

Design of Robust Lubricant-Infused Surfaces for Anti-Corrosion.

A lubricant-infused surface such as an oil-impregnated porous surface has great potentials for various applications due to its omniphobicity. However, the drainage and depletion of the lubricant liquid oil remain practical concerns for real applications. Here, we investigate the effect of a specially designed bottle-shaped nanopore of anodic aluminum oxide, which has a smaller pore diameter in the upper region than the lower one, on the oil retentivity and anti-corrosion efficacy. The effects of the viscosity and volatility of the lubricant oil were further investigated for synergy. Results show that the bottle-shaped pore helps to stably immobilize the lubricant oil in the nanostructure and significantly enhances the robustness and anti-corrosion efficacy, compared to the conventional cylindrical pores with straight walls as well as the hybrid one featured with additional pillar structures. Moreover, the enlarged oil capacity in the bottle-shaped pore allows the oil to cover the underlying metallic surface effectively at cracks, enhancing the damage tolerance with a unique self-healing capability. The oil with a higher viscosity further enhances the benefits so that the bottle-shaped pore impregnated with a higher-viscosity oil shows greater anti-corrosion efficacy. It suggests that the combination of the geometric features of nanopores and the fluid properties of lubricant liquid can lead to a maximized longevity and anti-corrosion efficacy of the liquid-infused surfaces for real applications.

Environmentally friendly preparation of robust superhydrophobic surfaces on stainless steel mesh

In this work, a robust surface with superhydrophobic properties was prepared on stainless steel mash by electrodeposition combined with low surface energy modification method. The wettability, phase composition, morphology and properties of the coating were characterized and tested using dynamic contact angle measuring instrument, X-ray diffraction (XRD), scanning electron microscopy (SEM) and other techniques. The experimental results show that the synergistic effect of dense petal-like micro-nano rough structures and stearic acid modification on the surface of stainless steel mesh endow the mesh with good superhydrophobicity, so the contact angle is even up to 170.3°. In addition, it had good performances of self-cleaning, anti-friction and oil-water separation. Its water contact angle was above 150.0° even after 230 cm friction distance. Its oil-water separation efficiency did not significantly decrease after 10 times of repeated use.

Robust and durable liquid-repellent surfaces.

Liquid-repellent surfaces, such as superhydrophobic surfaces, superoleophobic surfaces, and slippery liquid-infused surfaces, have drawn keen research interest from the communities engaged in chemical synthesis, interfacial chemistry, surface engineering, bionic manufacturing and micro-nano machining. This is due to their great potential applications in liquid-proofing, self-cleaning, chemical resistance, anti-icing, water/oil remediation, biomedicine, etc. However, poor robustness and durability that notably hinders the real-world applications of such surfaces remains their Achilles heel. The past few years have witnessed rapidly increasing publications that address the robustness and durability of liquid-repellent surfaces, and many breakthroughs have been achieved. This review provides an overview of the recent progress made towards robust and durable liquid-repellent surfaces. First, we discuss the wetting of solid surface and its generally-adopted characterisation methods, and introduce typical liquid-repellent surfaces. Second, we focus on various evaluation methods of the robustness and durability of liquid-repellent surfaces. Third, the recent advances in design and fabrication of robust and durable liquid-repellent surfaces are reviewed in detail. Fourth, we present the applications where these surfaces have been employed in fields like chemistry, engineering, biology and in daily life. Finally, we discuss the possible research perspectives in robust and durable liquid-repellent surfaces. By presenting such state-of-the-art of this significant and fast-developing area, we believe that this review will inspire multidisciplinary scientific communities and industrial circles to develop novel liquid-repellent surfaces that can meet the requirements of various real-world applications.

Design of robust superamphiphobic surfaces with enlarged area fractions: the considerable role of Laplace pressure in dynamics of contact lines.

Superamphiphobic surfaces have attracted widespread attention because of their great potential for applications in biotechnology, optoelectronics, water/oil separation, etc. Re-entrant curvatures are widely reported to provide a metastable Cassie state for superamphiphobicity. For high contact angles, re-entrant surfaces with a small area fraction (f) are designed according to the Cassie equation. However, this will make the surfaces take high local pressures under a mechanical force and thus suffer from frangibility. Robustness and high repellency are seemingly mutually exclusive. Herein, contrary to Cassie's equation, we show that high contact angles (>150°) with a large f (69.4%) of water and oleic acid can be achieved by utilizing a large upward Laplace pressure with narrow and parallel channel geometries. We deeply studied the effect of Laplace pressure on superamphiphobicity and suppose that the larger upward Laplace pressure stops the droplet earlier and pins the contact line at a higher position, providing a higher contact angle. The similar effect of viscous force well supports our explanation. These findings enable us to obtain robust and durable superamphiphobic surfaces with an enlarged area fraction and simple re-entrant microstructures. Our work may open up design strategies for robust superamphiphobic surfaces with practical applications.

Robust yet flexible slippery layered composite surfaces with a programmable pressure-resistance response under extreme environmental conditions

We present a universal strategy to produce robust yet flexible layered slippery surfaces. Based on these surfaces, the fabricated sensors possess outstanding stability in extreme working environments.

Facile fabrication of hierarchical textures for substrate-independent and durable superhydrophobic surfaces.

On account of their wide range of applications in self-cleaning, anti-icing, frost suppression, etc., superhydrophobic surfaces have attracted considerate attention. However, most of the superhydrophobic surfaces can only be prepared on the surfaces of specific materials and are easily damaged in the case of friction. In this work, we propose a facile method to achieve superhydrophobicity on various substrate surfaces. By femtosecond laser direct processing, micron-level grooves and protrusions are constructed on substrates to form a protective layer. Then, the substrates covered by polytetrafluoroethylene (PTFE) were scanned to make the surfaces of the substrates superhydrophobic. Since the PTFE micro-nano-particles are evenly distributed on the grooves and protrusions, the surfaces exhibit robust superhydrophobicity with excellent anti-friction performance that is independent of the substrate properties. This work provides an efficient and environmentally friendly path for achieving robust superhydrophobic surfaces on various substrates.

Per-fluorinated chemical free robust superhydrophobic copper surface using a scalable technique

Robust superhydrophobicity is of immense practical interest in a wide range of applications including self-cleaning, anti-icing, anti-corrosion, atmospheric water harvesting, desalination, condensation, and oil-water separation. However, biohazard associated with the prevalent use of per-fluorinated synthetic chemicals in making these surfaces and the gradual loss of superhydrophobicity have been major roadblocks. Here we develop an environment-friendly and industrially scalable superhydrophobic copper surface using a combination of electrochemical deposition and Lauric acid functionalization. We optimized the synthesis process for ensuring the robustness of these superhydrophobic surfaces. The surface exhibits contact angles as high as 158° with excellent droplet rebounding, self-cleaning, anti-icing, and dropwise condensation abilities. Thermal stability in the range of −15°C to 150°C, mechanical robustness against abrasion, chemical stability under aqueous, acidic, and basic medium, and the excellent plastron layer stability under long-time underwater immersion attest to the high quality of superhydrophobic surfaces for large-scale applications. These coatings when implemented on the curved surface of a copper tube demonstrated appreciable improvement in condensation behavior. Our method provides a sustainable approach for suitable technological interventions in energy and potable water applications requiring robust environment-friendly superhydrophobic surfaces.

One-step zwitterionization and quaternization of thick PDMAEMA layer grafted through subsurface-initiated ATRP for robust antibiofouling and antibacterial coating on PDMS

In this work, we demonstrate the grafting of thick poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA) layer on PDMS via subsurface-initiated atom transfer radical polymerization (SSI-ATRP). The self-migration of DMAEMA monomers into the subsurface of PDMS is proven to be the dominant factor for the success of SSI-ATRP. The as-prepared thick microscale graft layer on PDMS shows much better abrasion resistance than nanoscale graft layer obtained by conventional surface-initiated atom transfer radical polymerization (SI-ATRP) under identical condition. Taking advantage of the tertiary amines of PDMAEMA, the simultaneous zwitterionization and quaternization of the PDMAEMA thick layer is realized through a facile one-step process. The effect of zwitterionization and quaternization degree on the antibiofouling and antibacterial properties is investigated. The results show that a relatively high zwitterionization degree (75 mol%) and a low quaternization degree (25 mol%) exhibit a good well-balanced effect on both fouling repellence and bactericidal activity. This work may lead to the development of robust bifunctional antibiofouling and antibacterial surfaces via SSI-ATRP strategy.

Fabrication of Self-Healable, Robust Superhydrophobic Surfaces Using UV-Crosslinked Nanocomposite Films.

Studies on fabricating robust superhydrophobic surfaces by a low-cost method have been rare, despite the recent demand for nature-inspired superhydrophobic surfaces including self-healing ability in various industrial applications. Herein, we propose a fabrication method for self-healable, robust superhydrophobic nanocomposite films by facile solution-processed spray coating and UV curing. The components of the coating solution include functionalized hydrophobic silica nanoparticles for producing high roughness hierarchical textured structures with low surface energy, and UV-crosslinkable v-POSS and bi-thiol hydrocarbon molecules to improve the film stability. As a result of the synergetic effect of the hydrophobic nanoparticles and UV-crosslinked polymeric compounds, the spray-coated and UV-cured nanocomposite films possess excellent superhydrophobicity (water contact angles > 150º) and high stability, in addition to self-healing abilities.

Layer-by-layer assembly of nanofilms from colloidally stable amine-functionalized silica nanoparticles

The assembly of uniform thin films with functional silica nanoparticles (FSNPs) by the layer-by-layer (LbL) technique has been studied to provide rough, robust, and functional surfaces. Initially, monodisperse silica nanoparticles (SNPs) have been synthesized by the reverse microemulsion method. Then SNPs have been functionalized using amino silane coupling agents with various chain lengths and amine positions such as (3-aminopropyl)trimethoxy silane (APS), N-[3-(trimethoxysilyl)propyl]-N,N,N-trimethylammonium chloride (NPC), N -(6-aminohexyl)aminopropyltrimethoxy silane (AHAPS), and 3-aminopropyl(dimethyl)ethoxy silane (APDMES). The amine-functionalized silica nanoparticles have been characterized using zeta potential, Fourier Transform-Infrared Spectroscopy (FT-IR), and 1 H Nuclear Magnetic Resonance (NMR) spectroscopy to prove the existence of amine groups on the silica surface. Scanning electron microscopy (SEM) images have revealed that the LbL assembled thin film coatings of FSNPs are uniform and monodisperse. The thickness measurements of the coatings have been conducted by spectroscopic ellipsometry. Water contact angle measurements were performed to analyze the alteration of surface features with functional groups. The roughness, topography, and elastic modulus of the assembled thin-film coatings were probed by atomic force microscopy (AFM). The dispersion of AHAPS-FSNPs has indicated superior colloidal stability than other FSNPs because of their secondary amines creating steric hindrance. Moreover, AHAPS-FSNPs film exhibited the lowest coating thickness and the highest elastic modulus comparing with the other FSNPS because of their crosslinking and hydrogen-bonding ability. Briefly, in this work, LbL assembly of the amine FSNPs was established by an extensive investigation to form rough and functional surfaces for many demanding applications.

Making nanostructured materials from maize, milk and malacostraca

Nano-structured materials are used in electronics, diagnostics, therapeutics, smart packaging, energy management and textiles, areas critical for society and quality of life. However, their fabrication often places high demands on limited natural resources. Accordingly, renewable sources for the feedstocks used in their production are highly desirable. We demonstrate the use of readily available biopolymers derived from maize (zein), milk (casein) and malacostraca (crab-shell derived chitin) in conjunction with sacrificial templates, self-assembled monodisperse latex beads and anodized aluminium membranes, for producing robust surfaces coated with highly regular hyperporous networks or wire-like morphological features, respectively. The utility of this facile strategy for nano-structuring of biopolymers was demonstrated in a surface based-sensing application, where biotin-selective binding sites were generated in the zein-based nano-structured hyperporous network.

Facile preparation of robust superhydrophobic ceramic surfaces with mechanical stability, durability, and self-cleaning function

Superhydrophobic surfaces have aroused considerable attention because of their extensive potential applications, but such surfaces are mechanically weak which is a major limitation hindering their practical applications. Herein, we develop a facile strategy for fabricating robust superhydrophobic surfaces on zirconia ceramic substrates. The robust micro/nanostructured superhydrophobic surfaces are obtained via the direct ablation using a femtosecond laser without extra chemical modification. The experimental results demonstrate that the superhydrophobicity results from the special micro/nanostructures and the adsorbed chemical compounds from the air. Notably, these surfaces can retain their superhydrophobicity after being rubbed with an 800# grit sandpaper for 8 m at a contact pressure of 4.4 kPa, indicating superior mechanical stability. Moreover, the durability and self-cleaning functions of the obtained surfaces are also demonstrated. We envision that this work not only provides a facile and environmentally friendly approach for constructing robust superhydrophobic surfaces with excellent mechanical stability, but also inspires new applications of zirconia ceramics, especially in various extreme environments.

Recoverable underwater superhydrophobicity from a fully wetted state via dynamic air spreading

SummaryMaintaining the superhydrophobicity underwater offers drag resistance reduction, antifouling, anti-corrosion, noise reduction, and gas collection for boat hulls and submarine vehicles. However, superhydrophobicity typically does not last long underwater since the Cassie state is metastable. Here, we report a reversible and localized recovery of superhydrophobicity from the fully wetted state via air bubble spreading. Composed of sparse fluorinated chained nanoparticles, the submerged surface shows super-low energy barrier for bubble attachment. Especially the recovered plastron exhibits excellent longevity. Based on a simplified, truncated nanocone model, the dynamic spreading of bubbles is analyzed considering two basic parameters, i.e., surface geometric structure and surface energy (which appeared as intrinsic water contact angle). Numerical simulation results via COMSOL confirms the effect of geometric structure on bubble spreading. This investigation will not only offer new insights for the design of robust recoverable superhydrophobic surfaces but also broaden the applications of superhydrophobic coatings.