Underwater Superoleophobic Surfaces Research Articles

Regulating Underwater Oil Adhesion on Superoleophobic Copper Films through Assembling n-Alkanoic Acids.

Controlling liquid adhesion on special wetting surface is significant in many practical applications. In this paper, an easy self-assembled monolayer technique was advanced to modify nanostructured copper substrates, and tunable adhesive underwater superoleophobic surfaces were prepared. The surface adhesion can be regulated by simply varying the chain length of the n-alkanoic acids, and the tunable adhesive properties can be ascribed to the combined action of surfaces nanostructures and related variation in surface chemistry. Meanwhile, the tunable ability is universal, and the oil-adhesion controllability is suitable to various oils including silicon oil, n-hexane, and chloroform. Finally, on the basis of the special tunable adhesive properties, some applications of our surfaces including droplet storage, transfer, mixing, and so on are also discussed. The paper offers a novel and simple method to prepare underwater superoleophobic surfaces with regulated adhesion, which can potentially be applied in numerous fields, for instance, biodetection, microreactors, and microfluidic devices.

Cleaning of Oil Fouling with Water Enabled by Zwitterionic Polyelectrolyte Coatings: Overcoming the Imperative Challenge of Oil-Water Separation Membranes.

Herein we report a self-cleaning coating derived from zwitterionic poly(2-methacryloyloxylethyl phosphorylcholine) (PMPC) brushes grafted on a solid substrate. The PMPC surface not only exhibits complete oil repellency in a water-wetted state (i.e., underwater superoleophobicity), but also allows effective cleaning of oil fouled on dry surfaces by water alone. The PMPC surface was compared with typical underwater superoleophobic surfaces realized with the aid of surface roughening by applying hydrophilic nanostructures and those realized by applying smooth hydrophilic polyelectrolyte multilayers. We show that underwater superoleophobicity of a surface is not sufficient to enable water to clean up oil fouling on a dry surface, because the latter circumstance demands the surface to be able to strongly bond water not only in its pristine state but also in an oil-wetted state. The PMPC surface is unique with its described self-cleaning performance because the zwitterionic phosphorylcholine groups exhibit exceptional binding affinity to water even when they are already wetted by oil. Further, we show that applying this PMPC coating onto steel meshes produces oil-water separation membranes that are resilient to oil contamination with simply water rinsing. Consequently, we provide an effective solution to the oil contamination issue on the oil-water separation membranes, which is an imperative challenge in this field. Thanks to the self-cleaning effect of the PMPC surface, PMPC-coated steel meshes can not only separate oil from oil-water mixtures in a water-wetted state, but also can lift oil out from oil-water mixtures even in a dry state, which is a very promising technology for practical oil-spill remediation. In contrast, we show that oil contamination on conventional hydrophilic oil-water separation membranes would permanently induce the loss of oil-water separation function, and thus they have to be always used in a completely water-wetted state, which significantly restricts their application in practice.

Femtosecond laser controlling underwater oil-adhesion of glass surface

This paper presents a simple and effective method to fabricate underwater superoleophobic glass surfaces with extremely controllable oil-adhesion through the femtosecond laser microfabrication. The laser-irradiated surfaces show micro-/nanoscale hierarchical structures and similar underwater superoleophobicity. By adjusting the average distance of laser pulse focus, the oil-adhesion of the as-prepared underwater superoleophobic surfaces can be controlled from ultralow to ultrahigh. This controllability of oil-adhesion is ascribed to the different wetting states for the oil droplet on the surface that results from the change of the morphology and microstructure after femtosecond laser irradiation. The as-prepared superoleophobic surfaces with ultralow oil-adhesion have the anti-oil contamination ability in water. The ultrahigh oil-adhesive superoleophobic surfaces can be used as a “mechanical hand” to transfer small oil droplets without any volume loss in water environment, endowing the controllable oil-adhesive surfaces with important applications in the fusion of oil/organic microdroplets.

Bioinspired transparent underwater superoleophobic and anti-oil surfaces

A bioinspired method to realize transparent underwater superoleophobic and anti-oil surfaces by a femtosecond laser treatment.

Femtosecond Laser Induced Underwater Superoleophobic Surfaces

Femtosecond laser microfabrication has been recently utilized in interface science to modify the liquid wettability of solid surfaces. Silicon surface with hierarchical micro/nanostructure is fabricated by a femtosecond laser. Similar to the fish’s scales, the laser-induced surface shows superhydrophilicity in air and superoleophobicity underwater. The oil contact angles can reach up to 159.4 ± 1° for the 1,2-dichloroethane droplets in water. Besides, the surface exhibits ultralow oil-adhesion. In the oil/water/solid three-phase system, water can be trapped in the hierarchical rough structure and forms a repulsive oil layer according to underwater Cassie’s theory. The contact area between the asprepared surface and oil droplet is significantly reduced, resulting in superoleophobicity and ultralow oil-adhesion in water. In addition, transparent underwater superoleophobic and anti-oil surfaces are achieved on silica glass surfaces by femtosecond laser ablation. This transparent property is attributed to the presence of the water environment because scattering and refraction are effectively weakened. The presented method is simple and can accurately control the processing location, which may have widely potential applications in, for instance, microfluidics, biotechnologies, and antifouling coatings.

The design of underwater superoleophobic Ni/NiO microstructures with tunable oil adhesion.

Controlling oil adhesion in water is a fundamental issue in many practical applications for surfaces. Currently, almost all studies on underwater oil adhesion control are concentrated on regulating surface chemistry on polymer surfaces, and structure-dependent underwater oil adhesion is still rare, especially on inorganic materials. Herein, we report a series of underwater superoleophobic Ni/NiO surfaces with controlled oil adhesions by combining electro-deposition and heating techniques. The adhesive forces between an oil droplet and the surfaces can be adjusted from an extremely low (less than 1 μN) to a very high value (about 60 μN), and the tunable effect can be attributed to different wetting states that result from different microstructures on the surfaces. Moreover, the oil-adhesion controllability for different types of oils was also analyzed and the applications of the surface including oil droplet transportation and self-cleaning were discussed. The results reported herein provide a new feasible method for fabrication of underwater superoleophobic surfaces with controlled adhesion, and improve the understanding of the relationship between surface microstructures, adhesion, and the fabrication principle of tunable oil adhesive surfaces.

Oil/water separation with selective superantiwetting/superwetting surface materials.

The separation of oil from oily water is an important pursuit because of increasing worldwide oil pollution. Separation by the use of materials with selective oil/water absorption is a relatively recent area of development, yet highly promising. Owing to their selective superantiwetting/superwetting properties towards water and oil, superhydrophobic/superoleophilic surfaces and underwater superoleophobic surfaces have been developed for the separation of oil/water-free mixtures and emulsions. In this Review, after a short introduction to oil/water separation, we describe the principles of materials with selective oil/water absorption and outline recent advances in oil/water separation with superwetting/superantiwetting materials, including their design, their fabrication, and models of experimental setups. Finally, we discuss the current state of this new field and point out the remaining problems and future challenges.

An underwater superoleophobic surface that can be activated/deactivated via external triggers.

Poly[(2-dimethylamino)ethyl methacrylate] (pDMAEMA) brush surfaces were prepared using a facile aqueous Activators ReGenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET-ATRP) protocol at ambient temperature without any need to purge reaction solutions of oxygen. This produced underwater superoleophobic surfaces, which exhibited high advancing (θA, 164-166°) and receding (θR, 153-165°) contact angles (CAs) and low CA hysteresis (1-11°) with a variety of oils. Both in situ spectroscopic ellipsometry and dynamic CA measurements confirmed that pDMAEMA brush surfaces responded to three different external stimuli (pH, ionic strength, and temperature) by changing their thicknesses, degree of hydration, or their chemical composition. Increasing pH resulted in the largest decrease in hydration, followed by increasing temperature, and increasing ionic strength gave the smallest change in hydration. Coincident with these structural changes, stimulus-responsive dynamic dewetting behavior with various oils was observed. Increasing pH or ionic strength drastically reduced the θR values of oil drops and increased CA hysteresis, resulting in a sticky surface on which oil drops were pinned. No noticeable changes in dynamic oleophobicity were observed with increasing temperature. In addition, when oil drops impacted onto the brush surface instead of being gently placed, surfaces did not exhibit stimulus-responsive dewetting properties, being oleophobic under all conditions.

Substrate‐Independent Underwater Superoleophobic Surfaces Inspired by Fish‐Skin and Mussel‐Adhesives

Substrate-independent underwater superoleophobic surfaces are designed by combining two bio-inspirations: the remarkable oil-repellence of fish skin and the versatile anchoring ability of mussel-adhesive proteins. A mussel-inspired polymer is synthesized, showing strong underwater adhesion to various substrates. A fish-skin inspired top layer is then assembled on this polymer coating through a layer-by-layer process.

Wood-based microhaired superhydrophobic and underwater superoleophobic surfaces for oil/water separation

Wood-based microhaired superhydrophobic and underwater superoleophobic surfaces capable of effective oil/water mixtures separation are fabricated using a scalable replication technique.

Bioinspired underwater superoleophobic surface with ultralow oil-adhesion achieved by femtosecond laser microfabrication

A method to fabricate superoleophobic silicon surface with ultralow oil-adhesion using a femtosecond laser.

Nacre-Inspired Design of Mechanical Stable Coating with Underwater Superoleophobicity

Because of the frequent oil spill accidents in marine environment, stable superoleophobic coatings under seawater are highly desired. Current underwater superoleophobic surfaces often suffer from mechanical damages and lose their superoleophobicity gradually. It remains a challenge to fabricate a stable and robust underwater superoleophobic film which can endure harsh conditions in practical application. Nacre is one of most extensively studied rigid biological materials. Inspired by the outstanding mechanical property of seashell nacre and those underwater superoleophobic surfaces from nature, we fabricated a polyelectrolyte/clay hybrid film via typical layer-by-layer (LBL) method based on building blocks with high surface energy. 'Bricks-and-mortar' structure of seashell nacre was conceptually replicated into the prepared film, which endows the obtained film with excellent mechanical property and great abrasion resistance. In addtion, the prepared film also exhibits stable underwater superoleophobicity, low oil adhesion, and outstanding environment durability in artificial seawater. We anticipate that this work will provide a new method to design underwater low-oil-adhesion film with excellent mechanical property and improved stability, which may advance the practical applications in marine antifouling and microfluidic devices.

A facile approach for fabrication of underwater superoleophobic alloy

Superoleophobicity developed by creating roughness at multiple scales or lowering the surface energy has drawn extensive attention for technological applications. Currently, most methods for fabrication of superoleophobic surfaces employ either the complicated manufacture of micro/nano structures or delicate chemical decorations. Here, the sharp wetting transition from an oleophilic state to an oleophobic one has been practically realized, and the mechanism successfully interpreted. The underwater superoleophobic surfaces are newly realized and successfully controlled by subtly tuning the surface morphology of the alloy by practical corrosion plus a naturally obtained, stable, high-energy inorganic coating layer which induces the sharp wetting transition from oleophilic state to oleophobic state. The contact angle (CA) variations are quantitatively analyzed based on the wetting model by employing a roughness geometrical structure and a corrosion mechanism, which agree well with the measured results. Additionally, the dependence of the roughness on the corrosion procedure is modeled microscopically. Our method uncovers a facile fabrication protocol for optimum underwater superoleophobic surfaces by modifying the microstructures of alloy surfaces in the manufacturing process, which furthermore offers significant insights into the design and creation of other novel antifouling materials.

An underwater pH-responsive superoleophobic surface with reversibly switchable oil-adhesion

An underwater pH-responsive superoleophobic surface successfully demonstrated a reversible switch of oil-adhesion on a nanostructured poly(acrylic acid) (PAA) surface by changing the environmental pH values. At low pH, intramolecular hydrogen bonding of PAA is formed, and results in high oil-adhesion. As for high pH, the oil droplets can easily roll off due to the intermolecular hydrogen bonding between PAA and surrounding water.