Underwater Superoleophobic Surfaces Research Articles

Tribological properties of fish scale inspired underwater superoleophobic hierarchical structure in aqueous environment

Underwater superoleophobic surfaces are becoming increasingly important in regard to self-cleaning, anti-fouling, oil droplet transportation and water/oil separation. Although a great number of underwater superoleophobic surfaces have been demonstrated, their tribological properties remain impractical for the purposes of real-life applications. Herein, a two-step method of high speed wire electrical discharge machining and boiling water treatment was adopted to fabricate fish scale inspired underwater oil repellent hierarchical structure on an aluminum (Al) alloy 5083 surface. The hierarchical roughness and hydroxyl groups were obtained on the surface, and the surface exhibited the ability to prevent contact with organic fluids when submerged in water. Moreover, the tribological properties of underwater superoleophobic Al surfaces in aqueous environments were analyzed. The average friction coefficient of underwater superoleophobic surfaces was decreased compared with the polished Al surface. We believe that this research will contribute to the engineering application of underwater superoleophobic surfaces in the future.

Mechanically durable underwater superoleophobic surfaces based on hydrophilic bulk metals for oil/water separation

Despite the success of previous methods for fabricating underwater superoleophobic surfaces, most of the surfaces based on soft materials are prone to collapse and deformation due to their mechanically fragile nature, and they fail to perform their designed functions after the surface materials are damaged in water. In this work, the nanosecond laser-induced oxide coatings on hydrophilic bulk metals are reported which overcomes the limitation and shows the robust underwater superoleophobicity to a mechanical challenge encountered by surfaces deployed in water environment. The results show that the surface materials have the advantage that the underwater superoleophobicity is still preserved after the surfaces are scratched by knife or sandpaper and even completely destroyed because of the hydrophilic property of damaged materials in water. It is important that the results provide a guide for the design of durable underwater superoleophobic surfaces, and the development of superoleophobic materials in many potential applications such as the oil-repellent and the oil/water separation. Additionally, the nanosecond laser technology is simple, cost-effective and suitable for the large-area and mass fabrication of mechanically durable underwater superoleophobic metal materials.

A widely applicable method to fabricate underwater superoleophobic surfaces with low oil-adhesion on different metals by a femtosecond laser

In this paper, a one-step way to realize underwater superoleophobicity and low oil-adhesion on various metals by femtosecond laser ablation was proposed. The laser ablated aluminum surface showed hierarchical rough microstructure composed of abundant micro-holes and nano-particles. The oil contact angle on the as-prepared Al surface reached up to 157° and the oil sliding angle was just 7° to a 1,2-dichloroethane droplet in water. In addition, various oils including chloroform, hexadecane, n-dodecane, decane, liquid paraffin, and petroleum ether also showed underwater superoleophobicity on the structured aluminum surface. What’s more, other metals such as iron, copper, molybdenum, and stainless steel were ablated, respectively, through the same method. Due to the formation of rough microstructures and their intrinsic high surface energy, they all exhibited remarkable underwater ultralow oil-adhesive superoleophobicity. Such one-fit-all method with anti-oil-pollution can be a suit for an ocean of metals, which undoubtedly will be used in underwater precise instruments, such as vessels, underwater detectors, and oil–water separation device.

Fabrication and Wettability Study of WO3 Coated Photocatalytic Membrane for Oil-Water Separation: A Comparative Study with ZnO Coated Membrane

Superhydrophilic and underwater superoleophobic surfaces were fabricated by facile spray coating of nanostructured WO3 on stainless steel meshes and compared its performance in oil–water separation with ZnO coated meshes. The gravity driven oil-water separation system was designed using these surfaces as the separation media and it was noticed that WO3 coated stainless steel mesh showed high separation efficiency (99%), with pore size as high as 150 µm, whereas ZnO coated surfaces failed in the process of oil-water separation when the pore exceeded 50 µm size. Since, nanostructured WO3 is a well known catalyst, the simultaneous photocatalytic degradation of organic pollutants present in the separated water from the oil water separation process were tested using WO3 coated surfaces under UV radiation and the efficiency of this degradation was found to be quite significant. These results assure that with little improvisation on the oil water separation system, these surfaces can be made multifunctional to work simultaneously for oil-water separation and demineralization of organic pollutants from the separated water. Fabrication of the separating surface, their morphological characteristics, wettability, oil water separation efficiency and photo-catalytic degradation efficiency are enunciated.

Underwater Transparent Miniature "Mechanical Hand" Based on Femtosecond Laser-Induced Controllable Oil-Adhesive Patterned Glass for Oil Droplet Manipulation.

Development of underwater superoleophobic surfaces has captured the imagination of researchers because of their applications; especially, oil manipulation based on such surfaces has attracted much attention. Here, we show a simple and effective way to fabricate an underwater transparent miniature "mechanical hand" based on controllable oil-adhesive patterned glass using a femtosecond laser. The underwater oil-adhesive force of the patterned glasses that compose the "mechanical hand" device can be controlled from ultralow to ultrahigh by adjusting the ratio of the untreated flat glass area to the laser-ablated rough area. These surfaces also showed favorable transparency in water. Various oils such as chloroform, hexadecane, n-dodecane, decane, liquid paraffin, and petroleum ether were tested, and their repellency against the as-prepared surfaces in water medium was confirmed. Moreover, the "mechanical hand" was used to implement oil transportation, fusion, and rapid capture, which can be applied in the construction of microfluidic devices, in situ detectors, and bioreactors.

Versatile anti-fouling surface design through nature-inspired approaches

Nature-inspired artificial anti-fouling systems, including a superhydrophobic surface, a liquid-infused omniphobic slippery surface and an underwater oleophobic surface, have been proposed and are reviewed herein. An alumina gel film was applied as a platform for a superhydrophobic and an omniphobic slippery surface to ensure mechanical durability of the surface geometry and easy processing. The alumina gel film with hierarchical micro-/nanostructure composed of flower-like texture with 20–50 nm petals over the papilla geometry with a size scale of around 1 mm was prepared using the sol–gel process. The alumina gel film was successfully modified with perfluorodecyl phosphonic acid to introduce superhydrophobicity. Infusion of fluorinated non-volatile fluid into the nanostructured alumina gel film gave omniphobic slippery surfaces for both polar and non-polar liquids. Inspired by the wetting of fish skin and the strong adhesion of mussel adhesive protein, a novel substrate-independent underwater superoleophobic surface was developed. A catechol-bearing polymer was synthesized, which showed strong underwater adhesion with various substrates. Fish skin-inspired nanostructure was then created on this polymer-coated substrate through layer-by-layer assembly of poly(ethylenimine) and a high-molecular weight poly(acrylic acid), resulting in an underwater superoleophobic surface. Upon cross-linking, the obtained oleophobic surface became quite stable in water.

Inorganic Adhesives for Robust Superwetting Surfaces.

Superwetting surfaces require micro-/nanohierarchical structures but are mechanically weak. Moreover, such surfaces are easily polluted by amphiphiles. In this work, inorganic adhesives are presented as a building block for construction of superwetting surfaces and to promote robustness. Nanomaterials can be selected as fillers to endow the functions. We adopted a simple procedure to fabricate underwater superoleophobic surfaces by spraying a titanium dioxide suspension combined with aluminum phosphate binder on stainless steel meshes. The surfaces maintained their excellent performance in regard to oil repellency under water, oil/water separation, and self-cleaning properties after even 100 abrasion cycles with sandpaper. Robust superwetting surfaces favored by inorganic adhesives can be extended to other nanoparticles and substrates, which are potentially advantageous in practical applications.

Ultradurable underwater superoleophobic surfaces obtained by vapor-synthesized layered polymer nanocoatings for highly efficient oil–water separation

Layered polymer nanocoatings synthesized by vapor phase polymerization deposition enable underwater superoleophobic surfaces with excellent oil–water separation capability and ultradurability.

Femtosecond laser induced robust periodic nanoripple structured mesh for highly efficient oil-water separation.

Marine oil spills have induced severe water pollution and threatened sea ecosystems, which also result in a loss of energy resources. To deal with this problem, much work has been done for using superhydrophobic or superhydrophilic mesh for oil-water separation. Nevertheless, there are still great challenges in the rapid fabrication of extremely durable mesh with superwetting properties, particularly considering the highly efficient oil-water separation. In this study, we present a simple, efficient method to fabricate superhydrophilic and underwater superoleophobic stainless steel mesh surfaces with one-step femtosecond laser induced periodic nanoripple structures. The as-prepared mesh shows high separation efficiency, which is higher than 99% for various oil-water mixtures. More importantly, the wettability and the separation efficiency of the fabricated mesh show no obvious change after the abrasion tests and corrosion tests, indicating that the as-prepared samples possess robust stability. This study provides an efficient route for constructing durable and highly efficient separation mesh, which can be applied in the cleanup of large-scale oil spills in the near future.

Underwater superoleophobicity, anti-oil and ultra-broadband enhanced absorption of metallic surfaces produced by a femtosecond laser inspired by fish and chameleons.

Reported here is the bio-inspired and robust function of underwater superoleophobic, anti-oil metallic surfaces with ultra-broadband enhanced optical absorption obtained through femtosecond laser micromachining. Three distinct surface structures are fabricated using a wide variety of processing parameters. Underwater superoleophobic and anti-oil surfaces containing coral-like microstructures with nanoparticles and mount-like microstructures are achieved. These properties of the as-prepared surfaces exhibit good chemical stability when exposed to various types of oils and when immersed in water with a wide range of pH values. Moreover, coral-like microstructures with nanoparticle surfaces show strongly enhanced optical absorption over a broadband wavelength range from 0.2–25 μm. The potential mechanism for the excellent performance of the coral-like microstructures with a nanoparticle surface is also discussed. This multifunctional surface has potential applications in military submarines, amphibious military aircraft and tanks, and underwater anti-oil optical counter-reconnaissance devices.

Fabrication and applications of two- and three-dimensional curved surfaces with robust underwater superoleophobic properties

In this work, a method for the fabrication of two- and three-dimensional curved surfaces with robust underwater superoleophobicity is reported for the first time on light alloys (including 5083 Al and TC4 Ti alloys) through the high speed wire electrical discharge machining (HS-WEDM). The surface morphology and compositions were characterized by scanning electron microscope and energy-dispersive X-ray spectrometer. The results showed that rough structures and a layer of oxidization were created on the light alloys by HS-WEDM cutting. The two- and three-dimensional structured curved surfaces after an ethanol immersion exhibited the extreme underwater superoleophobic property with the high oil contact angle and low oil sliding angle. More importantly, the underwater superoleophobic surfaces with the three-dimensional curved features could have many new applications. In order to use the potential functions, the durability of the fabricated samples was tested and the results showed that the samples still exhibited the underwater superoleophobic property after the underwater storage and physical mechanism tests. Additionally, this method is versatile, simple, environment-friendly, and cost-effective.

Fabrication of Silica Nanospheres Coated Membranes: towards the Effective Separation of Oil-in-Water Emulsion in Extremely Acidic and Concentrated Salty Environments.

A superhydrophilic and underwater superoleophobic surface is fabricated by simply coating silica nanospheres onto a glass fiber membrane through a sol-gel process. Such membrane has a complex framework with micro and nano structures covering and presents a high efficiency (more than 98%) of oil-in-water emulsion separation under harsh environments including strong acidic and concentrated salty conditions. This membrane also possesses outstanding stability since no obvious decline in efficiency is observed after different kinds of oil-in-water emulsions separation, which provides it candidate for comprehensive applicability.

Bio-Inspired Design and Fabrication of Micro/Nano-Brush Dual Structural Surfaces for Switchable Oil Adhesion and Antifouling.

The underwater superoleophobic surfaces play a significant role in anti-oil contamination, marine antifouling, etc. Inspired by the Gecko's feet and its self-cleaning property, a hierarchical structure composed of poly (acrylic acid) gel micro-brushes is designed by the liquid-infused method. This surface exhibits underwater superoleophobicity with very low oil adhesion. It is then modified with stimuli-responsive polymer nano-brushes via surface-initiated atom transfer radical polymerization from the embedded initiator. The micro/nano-brush dual structural surfaces can switch the underwater oil adhesion between low and high while keeping the superoleophobicity. The antifouling properties against algae attachment under different mediums are also investigated to show a strong link between oleophobicity and antibiofouling property. The model surface will be very useful in directing the design of marine self-cleaning coatings to both living and non-living species.

Fabrication of Long-Term Underwater Superoleophobic Al Surfaces and Application on Underwater Lossless Manipulation of Non-Polar Organic Liquids

Underwater superoleophobic surfaces have different applications in fields from oil/water separation to underwater lossless manipulation. This kind of surfaces can be easily transformed from superhydrophilic surfaces in air, which means the stability of superhydrophilicity in air determines the stability of underwater superoleophobicity. However, superhydrophilic surfaces fabricated by some existing methods easily become hydrophobic or superhydrophobic in air with time. Here, a facile method combined with electrochemical etching and boiling water immersion is developed to fabricate long-term underwater superoleophobic surfaces. The surface morphologies and chemical compositions are investigated. The results show that the electrochemically etched and boiling-water immersed Al surfaces have excellent long-term superhydrophilicity in air for over 1 year and boehmite plays an important role in maintaining long-term stability of wettability. Based on the fabricated underwater superoleophobic surfaces, a special method and device were developed to realize the underwater lossless manipulation of immiscible organic liquid droplets with a large volume. The capture and release of liquid droplets were realized by controlling the resultant force of the applied driving pressure, gravity and buoyancy. The research has potential application in research-fields such as the transfer of valuable reagents, accurate control of miniature chemical reactions, droplet-based reactors, and eliminates contamination of manipulator components.

Superhydrophilic and underwater superoleophobic titania nanowires surface for oil repellency and oil/water separation

Superhydrophilic and underwater superoleophobic titania nanowires (TNWs) films on Ti substrates were fabricated via a facile low temperature and short time-consuming route. The hierarchical one-dimension nanowires morphology with considerable roughness of the films led to the water permeation in air and oil repellency in water. Not only in pure water, the as-prepared TNWs films also exhibited excellent underwater superoleophobicity in corrosive aqueous media, including highly saline, acidic and alkaline solutions. Importantly, the surface of the TNWs films may keep the wetting properties and morphologies after immersed into corrosive solutions for 168h, indicating the good environmental stability. The TNWs film prepared on Ti mesh showed good oil/water separation ability with a separation efficiency of high up to 99.7%. During the oil/water separation process, water passed through the mesh rapidly by gravity, while oils stayed above the mesh due to its superoleophobicity. We envision that the TNWs films with good underwater superoleophobicity may provide a candidate not only for oil/water separation but also in many other potential applications such as underwater oil manipulation, self-cleaning, bioadhesion control and fluidic devices.

Designing Bioinspired Anti-Biofouling Surfaces based on a Superwettability Strategy.

Anti-biofouling surfaces are of high importance owing to their crucial roles in biosensors, biomedical devices, food processing, the marine industry, etc. However, traditional anti-biofouling surfaces based on either the release of biocidal compounds or surface chemical/physical design cannot satisfy the practical demands when meeting real-world complex conditions. The outstanding performances of natural anti-biofouling surfaces motivate the development of new bioinspired anti-biofouling surfaces. Herein, a novel strategy is proposed for rationally designing bioinspired anti-biofouling surfaces based on superwettability. By utilizing the trapped air cushions or liquid layers, Lotus leaf inspired superhydrophobic surfaces, fish scales inspired underwater superoleophobic surfaces, and Nepenthes pitcher plants inspired omniphobic slippery surfaces have been successfully designed as anti-biofouling surfaces to effectively resist proteins, bacteria, cells, and marine organisms. It is believed that these novel superwettability-based anti-biofouling surfaces will bring a new era to both biomedical technology and the marine industry, and will greatly benefit human health and daily life in the near future.

Recent Development of Durable and Self-Healing Surfaces with Special Wettability.

Artificial special wetting surfaces have drawn much interest due to their important applications in many fields. Nevertheless, tremendous challenges still remain for the fabrication of wetting surfaces with durable and self-healing properties. Here, recent progress of durable, self-healing wetting surfaces is highlighted by discussing the fabrications of several typical wetting surfaces including superhydrophobic surfaces, superamphiphobic surfaces, underwater superoleophobic surfaces, and high hydrophilic antifouling surfaces based on expertise and related research experience. To conclude, some perspectives on the future research and development of these special wetting surfaces are presented.

Preparation of durable underwater superoleophobic Ti6Al4V surfaces by electrochemical etching

Underwater superoleophobic Ti6Al4V surfaces were fabricated successfully via electrochemical etching. The morphologies, chemical compositions and crystal structures of the prepared titanium alloy surfaces were characterised by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction, respectively. The relationship between the etching time and oil wettability in water was investigated and the formation mechanism of hierarchical micro/nano rough structures on titanium alloy surfaces was also carefully analysed. Further, a series of exposure, immersion and abrasion tests were conducted to evaluate durability, corrosion resistance and abrasion resistance of the fabricated titanium alloy surfaces under harsh conditions. The results show that the prepared surfaces exhibit good underwater superoleophobicity, whose oil contact angle for dichloromethane in water is 158.9° ± 1.7° and corresponding sliding angle is 6.4° ± 1.4°. Our approach is simple, efficient and may broaden the potential applications of superoleophobic titanium alloy surfaces in underwater self-cleaning and anti-oil pollution fields.

Underwater superoleophobic carbon nanotubes/core–shell polystyrene@Au nanoparticles composite membrane for flow-through catalytic decomposition and oil/water separation

A hierarchical composite membrane with underwater superoleophobic surface and underlying catalytic microspheres is fabricated to achieve simultaneous flow-through catalytic decomposition and oil/water separation.

Magnetic field actuated manipulation and transfer of oil droplets on a stable underwater superoleophobic surface.

The transport of fluids at functional interfaces, driven by the external stimuli, is well established. The lossless transport of oil-based fluids under water remains a challenge, however, due to their high stickiness towards the surface. Here, a superhydrophilic and underwater superoleophobic tri-phase water/oil/solid nanoarray surface has been designed and prepared. The unique tri-phase surface exhibits underwater superoleophobic properties with an extremely low stickiness towards oil-based fluids. The magnetic-field-driven manipulation and transport of oil-based magnetic fluids are demonstrated under water, which opens up a new pathway to design flexible and smart devices for the control and transfer of liquid droplets by using tri-phase systems.