Superoleophilic Surface Research Articles

Environmentally friendly SLIPS coating based on flexible sponge: A novel approach to antifouling for ships

To mitigate the attachment of fouling organisms, Slippery Liquid-Infused Porous Surfaces (SLIPS) hold tremendous potential as a green and broad-spectrum antifouling solution, capable of replacing traditional antifouling coatings. However, the complexity of current preparation methods and the limited lifespan of lubricating oils constrain their widespread application in marine antifouling for vessels. In this study, melamine sponge (MS) was used as a substrate, and modifications were made by introducing superhydrophobic silica nanoparticles (SiO2 NPs), a biocompatible adhesive (ethyl cyanoacrylate, ECA), and a highly stretchable polymer (poly-ε-caprolactone, PCL). By combining natural surface microstructures with additional nanomaterials, we successfully obtained a superoleophilic surface, effectively capturing liquid lubricants and maintaining their long-term stability. The sponge substrate possesses distinctive contractility, with the lubricant stored in the grid spontaneously compensating for the loss of surface lubricant, thereby effectively enhancing its durability. This study provides a straightforward fabrication method with reduced manufacturing costs for environmentally friendly marine anti-fouling coatings. The approach demonstrates a prolonged cyclic anti-fouling effect, effectively advancing the development of SLIPS for anti-fouling applications in shallow marine environments.

Attaining superhydrophobic and superoleophilic bronze surface by picosecond laser texturing and post-heat treatment

As a bearing material, bronze has high strength and hardness but is poor in anti-adhesion property. In this study, we propose a method to prepare a superhydrophobic and superoleophilic bronze surface by combining laser surface texturing and post-heat treatment. A picosecond laser was employed to produce pore arrays with varying spacings and depths on the bronze surface, which exhibited micro-nano hierarchical structures. A further post-heat treatment of the laser-textured sample at 150 °C in the ambient led to the formation of a superhydrophobic surface with a maximum water contact angle of 158° and with superoleophilicity. It was found that pore spacings played a significant role in forming the surface hierarchical structures, which were covered with the laser-ablated micro-nano particles. The pore depth, however, showed little influence on the surface wettability. Analysis of the surface chemical compositions by X-ray photoelectron spectroscopy (XPS) indicates that the C element mainly exists in the form of the C–C(H) group, which reduces the surface energy and leads to superhydrophobicity. It was also verified that the wettability transition of the bronze surface before and after heating was independent of the oxide transition. Rubbing tests were conducted to evaluate the durability of the surface hierarchical structure. Anti-icing and self-cleaning functions were demonstrated showing the potential of the developed method for preparing a superhydrophobic and superoleophilic surface.

A bioinspired vine-like hierarchically structured PET/CA composite nanofibrous membrane with superhydrophobic and superoleophilic surface for high-efficiency cooking fumes capture

Indoor air pollution, especially from cooking oil fumes (COFs), has become a serious issue that affects human health. Obtaining filters that can offer high efficiency, high air permeability and good reusability and stability for COFs removal remains a challenge. Herein, a bioinspired vine-like polyethylene terephthalate/cellulose acetate (PET/CA) composite nanofibrous membrane with high filtration performance, high air permeability and enhanced flame retardancy for COFs removal is achieved via a one-step co-electrospinning process. The nanofibrous membrane consists of hierarchically branched nanofibers to offer small pore size (0.48 μm), high porosity (94.75 %) and low packing density (0.22 g m−3), as well as surface superhydrophobicity (water contact angle of 154°) and superoleophilicity (vegetable oil wetting time of 0.21 s). The nanofibrous filter demonstrates high-efficiency COFs removal (>99.5 %), low air resistance (<70 Pa) and good reusability and stability for actual COFs purification. By virtue of the simple fabrication technique and the superiorities in COFs capture, the bioinspired vine-like hierarchical structured nanofibrous membranes have promising applications for oily fumes filtration and air purification in the catering industry.

Nanocomposite PVDF Membrane for Battery Separator Prepared via Hot Pressing

Polyvinylidene fluoride (PVDF) is one of the materials most commonly used in membrane separators. The structures of pristine PVDF and PVDF nanocomposite films were processed via hot pressing at 140 °C, 170 °C, and 185 °C at a pressure of 2 tons for 15 min. According to a surface investigation using scanning electron microscopy (SEM), the spherulitic character of the PVDF nanocomposite films was preserved up to a pressing temperatures of 140 °C. The cross-sectional SEM images confirmed that higher pressing temperatures (170 °C) caused the structures to be compacted into monolithic films, and a pressing temperature of 185 °C caused the melting of the PVDF matrix and its recrystallization into thin films (21–29 μm). An average crystallinity value of 51.5% was calculated using differential scanning calorimetry (DSC), and this decreased as the pressing temperature increased. Fourier transform infrared (FTIR) measurements confirmed the presence of a dominant γ phases in the PVDF nanocomposite films, whose nanofillers consisted of vermiculite particles (ZnO_V and ZnO_V_CH) and mixed α + γ phases. The percentage of the electroactive γ phase (approximately 79%) was calculated via a FTIR analysis, and the ratio between the β phase and the α phase was determined from the Raman spectra. A hydrophilic surface with contact angles ranging from 61 to 84° was demonstrated for all the PVDF nanocomposite membranes. The superoleophilic surface was measured using poly(dimethylsiloxane) with contact angles ranging from 4 to 13°, and these angles reached lower values when in contact with sulfur particles.

Superhydrophobic and superoleophilic surfaces prepared by one-step plasma polymerization for oil-water separation and self-cleaning function

Efficient superhydrophobic and superoleophilic thin films for oil-water separation and self-cleaning were prepared using the atmospheric-pressure plasma polymerization of hexamethyldisiloxane (HMDSO). A dielectric barrier discharge (DBD) plasma jet with argon (Ar) was used for the deposition of the functional thin films onto several substrates. The oil-water separation membrane was synthesized by the plasma polymerization of HMDSO on fabric and offset printing paper. The superhydrophobic coatings were deposited on glass to demonstrate their self-cleaning ability. The hydrophobicity of the thin films was found to vary significantly, depending on the operating parameters such as the deposition time, applied voltage, and gas flow rate. The gaseous shield of the plasma jet also affected the hydrophobicity to a large extent. Nitrogen (N2) rather than inert gases such as Ar and He exhibited an excellent shielding effect against the interference of ambient air on the plasma jet. The wettability of the glass was completely switched from superhydrophilic to superhydrophobic with the water contact angle (WCA) reaching 165° and the sliding angle about 2°. In addition, superoleophilicity was obtained with the oil contact angle (OCA) reaching 0° under the optimal operating conditions.

Fluorine-free superhydrophobic cotton fabric for highly-efficient gravity-driven oil/water separation

Rapid urbanisation and industrialisation have imposed great environmental impact due to the discharge of oily wastewater and oil spill incidents. The application of superhydrophobic and superoleophilic surfaces in oil/water separation (OWS) has attracted much attention due to their high selectivity of oil which leads to high separation efficiency in OWS. Herein, a fluorine-free superhydrophobic cotton fabric filter was prepared by loading SiO2 onto the surface from the silica sol and followed by coating with stearic acid through facile dip coating method. The silica sol was prepared using tetraethyl orthosilicate (TEOS) where the loading was manipulated in order to study its effect on hydrophobicity. In the drying process, the effect of the drying temperature on the hydrophobicity was studied. All the pristine and modified cotton fabric samples were characterised by employing FTIR, SEM-EDX and water contact angle measurement. In the preparation process, the optimum TEOS loading was determined to be 4.5 mL. Additionally, the as-prepared superhydrophobic cotton fabric was used to perform OWS, under sole influence of gravity, by using different oil-water mixture solutions and the separation efficiency was above 99%. The results showed that higher drying temperature gives rise in hydrophobicity, and thus lead to more efficient OWS.

Biomimetic Janus photonic soft actuator with structural color self-reporting.

Soft actuators with variable signal/color play an important role in the fields of targeted locomotion, artificial phototropism, drug screening, cargo transportation, and interactive sensing. The ability to achieve rapid response, large curvature, wide bending angle, and full-color display continues to be an unresolved challenge for artificial actuating materials. Inspired by the angle-dependent structural color of broad-tailed hummingbird and the Janus wettability of the lotus leaf, a Janus photonic soft actuator (JPSA) was fabricated by integrating an underwater super-oleophilic copper micro-nano array and oil-phobic inverse opal through a Laplace channel. The JPSA exhibits unidirectional permeability to underwater oil droplets. Attractively, with the combination of a swellable super-oleophilic surface and photonic crystals, JPSAs were endowed with oil-controlled reversible bending behavior with self-reporting angle-dependent color indication. We described for the first time the directional actuating mechanism induced by underwater oil unidirectional penetration and revealed the corresponding actuating kinetics and the inner-stress distribution/transfer by using structural color. As an extension of such theory, a rapid responsive JPSA with a wide bending angle and full-color self-reporting is further fabricated. This work provides an efficient strategy for oil directional transportation and separation in aqueous media and inspires the fabrication of a soft actuator/sensor with structural color self-reporting.

Pickering emulsion strategy to control surface wettability of polymer microspheres for oil–water separation

Surface wettability, one of the most important parameters for oil–water separation, depends on the chemical composition and surface roughness of a material. Herein, the Pickering emulsion template method is proposed to control the surface wettability of polymer microspheres. Upon the dispersion of modified diatomite particles in the aqueous phase, a superhydrophobic surface was formed on the polymer microspheres via Pickering emulsion polymerization, with a water contact angle of 152°. When the initial dispersion location of the modified diatomite particles changed from water to oil, a hydrophilic/underwater superoleophilic surface with micro/nanoscale hierarchical structures formed on the polymer microspheres. This special wettability enabled the microsphere layer to serve as an adsorbent with underwater superoleophilicity, achieving efficient oil separation from various oil-in-water emulsions with high separation efficiency of >99.8%. Hence, this study provides a valuable strategy based on the Pickering emulsion template method to design materials with special wettability for realizing promising emulsion separation.

Nanosecond laser fabrication of superwetting surface on Cu foam for oil-water separation and oil recovery

Oily wastewater has caused adverse affects on the ecology. In contrast, how to effectively treat the wastewater and recover oil has been a challenge. Herein, we proposed a facile and cost-effective method to solve problem. A copper foam was fabricated by one-step nanosecond laser patterning for the first time and a superwetting surface was obtained. By adjusting ablation parameters, a superhydrophobic and superoleophilic surface was obtained whose water contact angle (WCA) was about 154.5° and oil contact angle (OCA) was 0° in air. In addition, surface morphology and elementary composition were characterized by scanning electron microscopy (SEM) and energy dispersive X-Ray (EDX) spectroscopy respectively. It is obvious hierarchical micro-nano structures were formed on the surface mainly caused by Cu melting and recasting during ablation. The ablated surfaces can be used not only for oil-water separation, but also for oil recovery with the recovery efficiency reaching 100%. Moreover, the surface exhibited outstanding stability which can be used for repeatable oil recovery application.

Nanosecond Laser Fabrication of Superhydrophobic and Superoleophilic Surface on Copper Foam

Nanosecond Laser Fabrication of Superhydrophobic and Superoleophilic Surface on Copper Foam

Novel superhydrophobic surface of cotton fabrics for removing oil or organic solvents from contaminated water

Surface science such as superhydrophobic and superoleophilic surfaces plays a sensitive function in a separating oil/water mixture as a result of increasing industrial oil and organic solvents drainage occurrence. In this work, copper hydroxide nanoneedles layer were synthesized onto Egyptian cotton fabrics (CF) treated with polydopamine, Ag nanoparticles (NPs) and Cu NPs via facile immersion process. Fourier transform infrared, X-ray diffraction and scanning electron microscope (SEM) were used to investigate the functionalized surface of CF with copper hydroxide layer. SEM images confirmed that the modified membranes were rougher compared with pure surface of CF. The contact angle measurement emphasized the hydrophobicity of the modified membranes and it was found that the water contact angle has a value of 168°. The absorption capacity of the modified CF membrane was 10.1 g g − 1 for diesel oil and the separation efficiency of this modified surface was higher than 99%. It was noted that the flux in the case of low viscosity solvent as n-hexane was 72,172.9 Lm− 2 h− 1, while for the viscous oil as diesel was 14,460.3 Lm− 2 h− 1.

Novel BiOCl/BiCl3Br–CTA Heterostructure Photocatalyst with Abundant Oxygen Vacancies and a Superoleophilic Surface for Promoting Selective Oxidation of Toluene

A heterostructure photocatalyst consisting of BiOCl nanoplates and a bismuth-organic hybrid layer (alias BiCl3Br–CTA) was synthesized through a one-step solvothermal process. The BiOCl/BiCl3Br–CTA heterostructures exhibited broad light absorption and enhanced electron–hole separation efficiency. Moreover, the abundant oxygen vacancies (OVs) and superoleophilic surface endowed the photocatalyst with high abilities for adsorption and activation of O2 and toluene. Therefore, the BiOCl/BiCl3Br–CTA photocatalyst showed excellent activities for the C­(sp3)–H bond oxidation of toluene under full-spectrum irradiation and visible light of simulated sunlight, which are 6.8-fold and 237.8-fold, respectively, than those of BiOCl nanoplates. The photocatalytic mechanism was revealed by a series of controlled experiments and in situ ESR detections. The selective oxidation of toluene was promoted by the synergy between the electrons in BiOCl for activating O2 and the holes in the BiCl3Br–CTA layer for activating the C­(sp3)–H bonds. This research demonstrates an effective strategy to construct high-activity photocatalysts for challenging organic transformations.

Preparation of superhydrophobic and superoleophilic polylactic acid nonwoven filter for oil/Water separation

Superhydrophobic and superoleophilic surfaces exhibit a remarkable feature in separation of oil from oily wastewaters. In this work, a green superhydrophobic/ superoleophilic polylactic acid (PLA) nonwoven filter was prepared via a non-solvent assisted phase separation method. The results showed addition of non-solvent endowed the PLA nonwoven filter with typical micro/nano hierarchical structures and high porosity. Moreover, the resultant filter exhibited excellent oil/water separation efficiency more than 95% for various kinds of oils or solvents. In addition, the filter maintained favorable recycle ability even after 20 separation cycles. Therefore, the PLA nonwoven filter showed a high separation efficiency and an excellent recyclability, which is potential in rapid separation of oil/water mixture for ocean pollution cleanup.

Super-hydrophobic and super-oleophilic surface based on high-density polyethylene/waste ground rubber tire powder thermoplastic elastomer

Super-hydrophobic and super-oleophilic surface based on high-density polyethylene/styrene–butadiene–styrene block copolymer/waste ground rubber tire powder thermoplastic elastomer (TPE) was successfully prepared while metallographic sandpaper was used as a template. Field emission scanning electron microscope study showed that the molded TPE surface with W7 grade sandpaper possessed the rough microstructure; moreover, the micrometer scale strips resulting from the plastic deformation of TPE matrix could be observed obviously, leading to the increasing surface roughness. Wettability tests showed that the molded TPE surfaces with series sandpapers exhibited the hydrophobic and super-oleophilic properties; moreover, the surface molded with W7 grade sandpaper showed the remarkable super-hydrophobic and super-oleophilic properties.

Facile fabrication of superhydrophobic and superoleophilic green ceramic hollow fiber membrane derived from waste sugarcane bagasse ash for oil/water separation

Green ceramic hollow fiber membranes with superhydrophobic and superoleophilic surfaces (ss-CHFM/WSBA) were successfully fabricated via facile sol–gel process using tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as precursors. In this work, silica solution was prepared using the modified Stöber method. This process was followed by dipping the pristine membranes into the sol–gel solution at various grafting times (0–90 min), grafting cycles (0–4 cycles), and calcination temperatures (400–600 °C). The wettability, surface morphology, and chemical composition of the pristine and ss-CHFM/WSBA membranes were investigated. The results showed that increasing the grafting time has increased the wettability of ss-CHFM/WSBA with high contact angle of up to 163.9°. Similarly, increasing grafting cycle has enhanced the hydrophobicity of ss-CHFM/WSBA due to the formation of hierarchical structure of grafting cycle which were more than one. The optimum calcination temperature for ss-CHFM/WSBA was identified. It was found that increasing the calcination temperature has degraded the sol template on the surface of ss-CHFM/WSBA, hence decreasing the wettability. The preliminary performance tests showed that ss-CHFM/WSBA grafted at 60 min, 3 cycles, and calcined at 400 °C showed excellent oil/water separation efficiency of 99.9% and oil flux of 137.2 L/m2h.

Dynamics of capillary flow in an open superoleophilic microchannel and its application to sensing of oil

We report the dynamics of capillary flow of oil in an open superoleophilic channel. The superoleophilic surface is fabricated by spin coating a layer of PDMS + n-hexane followed by candle sooting. The occurrence of various flow regimes, including the inertial, visco-inertial, and Lucas–Washburn regimes, are studied using analytical modelling as well as experiments. In case of a superoleophilic channel, much shorter inertial regime is observed as compared to that in an oleophilic channel due to the wicking of oil into the micro-roughness grooves ahead to moving bulk liquid meniscus. The study of the effect of channel aspect ratio $$\varepsilon$$ on the mobility parameter $$k~$$ showed that the mobility parameter $$k$$ is maximum for an aspect ratio of $$\varepsilon =1.6$$ , which is attributed to the balance between the capillary and viscous forces. Finally, we demonstrate the application of the superoleophilic channel integrated with electrodes for impedance-based sensing of oil from an oil–water emulsion.

Superhydrophobic and superoleophilic surfaces prepared by spray-coating of facile synthesized Cerium(IV) oxide nanoparticles for efficient oil/water separation

In this work, we report the preparation of superhydrophobic and superoleophilic surfaces on stainless steel meshes by spray-coating of Cerium(IV) oxide (CeO2) nanoparticles obtained by a co-precipitation method. The synthesized particles and the coated meshes were characterized using advanced techniques. Scanning electron microscopy images showed the particles to be present in distinct lumps; merged with each other on calcination to give a homogeneous structure. Transmission electron microscopy analyses showed the agglomeration of individual particles to form the clusters. Contact angle measurements revealed the superhydrophobic and superoleophilic nature of the modified mesh surface in air. Fourier transform infra-red analyses of the synthesized particles showed the characteristics peaks of CeO2 found in commercial samples. X-ray photoelectron spectroscopy of the glass coated with ceria confirmed the predominant presence of Ce4+ that also explained the wetting behavior. Oil-water separation studies using a simple gravity-driven setup showed high separation efficiency of an oil water mixture. An analytical model is discussed in detail to account for the wetting behavior and efficacy of the prepared surfaces in separating the two fluids. To summarize, this work presents a very simple and effective route for oil-water separation with high efficiency.

One-step method for fabrication of superhydrophobic and superoleophilic surface for water-oil separation

A superhydrophobic and superoleophilic surface with micro-nano-binary scale structure and low surface energy coating was fabricated via one-step anodization process based on bare copper wire mesh. The water contact angle and water sliding angle of the prepared surface were 153° and 7.5° respectively, and the oil contact angle was 0°, the prepared surface showed excellent water repelling ability and superior absorption capacity for oil. Moreover, the prepared surface exhibits good resistance to saturation and corrosion. Furthermore, the prepared surface could separate many kinds of oil-water mixture efficiently. Even after 10 cycles, the separation efficiency still could reach above 87%. This study provided a low-cost and facial route to fabricate the surface which had high water-oil separation efficiency and excellent durability. Therefore this method had a promising application prospect.

Nanofibrous polystyrene membranes prepared through solution blow spinning with an airbrush and the facile application in oil recovery

Polystyrene (PS) dissolved in dichloromethane was spun to prepare the nanofibrous polystyrene membranes (NPS) through solution blow spinning with a commercialized airbrush. The influences of spinning conditions on the membrane morphology, density, and porosity were investigated. Through varying the PS concentration (8%, 9%, 10%), gas pressure (0.1, 0.2, 0.3 MPa), and acceptance distance (10, 12, 15, 18 cm), NPS with diameters of 200–1400 nm were prepared. The membranes had high porosity of 83.9%, and super-hydrophobic and super-oleophilic surface. The oil absorbency to motor oil, peanut oil, diesel oil, and heavy oil was 29.35, 27.27, 21.81, and 22.80 g/g, respectively, while that of the commercialized nonwoven polypropylene was 9.34, 9.17, 7.09, and 7.79 g/g, respectively. NPS could separate oil from water surface in several seconds. It was easy to prepare the membrane in situ on the surface of an oil/water mixture and remove the oil while peeling off the membrane, indicating NPS is potential as oil recovery material in large-area oil pollution environment.

One-step fabrication of robust superhydrophobic and superoleophilic surfaces with self-cleaning and oil/water separation function

Superhydrophobic surfaces have great potential for application in self-cleaning and oil/water separation. However, the large-scale practical applications of superhydrophobic coating surfaces are impeded by many factors, such as complicated fabrication processes, the use of fluorinated reagents and noxious organic solvents and poor mechanical stability. Herein, we describe the successful preparation of a fluorine-free multifunctional coating without noxious organic solvents that was brushed, dipped or sprayed onto glass slides and stainless-steel meshes as substrates. The obtained multifunctional superhydrophobic and superoleophilic surfaces (MSHOs) demonstrated self-cleaning abilities even when contaminated with or immersed in oil. The superhydrophobic surfaces were robust and maintained their water repellency after being scratched with a knife or abraded with sandpaper for 50 cycles. In addition, stainless-steel meshes sprayed with the coating quickly separated various oil/water mixtures with a high separation efficiency (>93%). Furthermore, the coated mesh maintained a high separation efficiency above 95% over 20 cycles of separation. This simple and effective strategy will inspire the large-scale fabrication of multifunctional surfaces for practical applications in self-cleaning and oil/water separation.