Oil Contact Angle Research Articles

Underwater superoleophobic GO-PEI-SiO2-Hal quaternary sphere-rod nacre-inspired mesh by LBL self-assembly for high-efficiency oil-water separation

The easy preparation of robust superwetting materials for oily wastewater disposal still remains a challenge. Inspired by the self-cleaning and mechanical properties of natural nacre underwater, herein, we have successfully developed sphere-rod quaternary artificial nacre-inspired meshes (named GO-PEI-SiO2-Hal) via interfacial self-assembly using 2D graphene oxide nanosheets, hyperbranched polyethyleneimine, SiO2 nanospheres, and hollow halloysite nanotubes (Hal) as the building blocks. The nacre-like “brick-and-mortar” layered microstructure was successfully formed and tightly coated to the mesh, showing excellent mechanical properties with Young's modulus up to 19.7 ± 2.6 GPa. Compared to the ternary structures, the quaternary sphere-rod morphology improved the surface roughness, and these four organic/inorganic building blocks are all hydrophilic, which together resulted in the superhydrophilic and underwater superoleophobic characteristics. The effects of building block concentration, dipping number, and mesh size on wettability and oil-water separation performance were studied in detail. The optimal (GO-PEI-SiO2-Hal-1)15@Fe300 mesh showed an underwater oil contact angle of 159o for 1,2-dichloroethane, low oil adhesion, and excellent separation efficiency up to 99.8% at an ultrahigh flux up to 195,038 L m−2 h−1. This nacre-like mesh exhibited excellent salt tolerance, acid-alkali resistance, recycling ability, and mechanical properties for practical oily wastewater treatment.

Hyper cross-linked poly(ionic liquid)s with special anions as “smart materials” for switchable oil-water separation

Smart materials with superhydrophobic-superlipophobic switchability can selectively penetrate one phase (oil or water) through the surface, and the other is trapped. In this study, several super wetting materials were fabricated based on the modulation of Friedel–Crafts alkylation and ion exchange on hyper cross-linked poly(ionic liquid)s (HCPILs) properties. They showed high oil-water separation efficiency in different complex environments. These synthetic HCPILs exhibit different hydrophilicity or lipophilicity when containing various anions. In particular, the HCPIL with a hexafluorophosphate (HCPIL-PF6) or a bis(trifluoromethylsulfonyl)imide (HCPIL-TF2N) possesses a switchable super wetting property due to its unique surface structure and chemical composition. They can be freely switched between hyperhydrophilicity and hyperlipophilicity according to the corresponding solvent changes and are suitable for separating many oil-water mixtures, especially the emulsions. The respective separation flux of the oil-water mixture or lotion is up to 9450 L/m2·h and 800.32 L/m2·h. Besides, they have strong durability and stability in harsh environments such as high concentrations of salt, acid, and basic solutions. After dozens of cycles, they can maintain efficient oil-water separation efficiency and exhibit a high underwater oil contact angle or underoil water contact angle. Such smart materials have great potential in various practical applications, providing a significant idea for future continuous production.

Design and synthesis of low surface energy anhydride-based polyacrylic resin

Surfaces with micro–nano roughness and reduced surface energy owing to long-chain fluorocarbon oligomers are critical for developing superamphiphobic surfaces. Here, a series of anhydride-based polypropylene (MPA) resins with different substituents (R) in their side chains were synthesized by the radical polymerization of (meth) acrylates, styrene, and maleic anhydride. Static-oil and water contact angle tests were conducted on the MPA film, which demonstrated that the longer the carbon chain in the side chain substituent, the stronger the hydrophobicity of the coating, and the higher the fluorine content in the side chain, the higher the oleophobicity. The MPA coating with long-chain alkane side chains (R = C18H37) exhibited the greatest hydrophobicity (water contact and sliding angles of 130° and 65°, respectively). However, the MPA coating with long-chain alkanes showed poor oil repellency to non-polar solvents (oil phase). When (R) = C8F17, the coating exhibited high oleophobicity but poor friction resistance. Based on these results, a low surface energy MPA coating was designed by combining long-chain alkane groups with fluorocarbon groups. The optimized coating with a 0.8:0.4 molecular ratio of stearyl methylacrylate to 1H,1H,2H,2H-heptadecafluorodecyl acrylate exhibited both water and oil repellency (water and oil contact angles of 135° and 95°, respectively) and adequate mechanical properties.

Micro/nano structured oleophobic agent improving the wellbore stability of shale gas wells

Through embedding modified nano-silica particles on the surface of polystyrene using the method of Pickering emulsion polymerization, a kind of nano/micro oleophobic agent named OL-1 was developed. The effects of OL-1 on the rock surface properties and its performance in inhibiting the oil phase imbibition into the rock were explored. The performance and mechanisms of OL-1 in improving the wellbore stability of shale gas wells were evaluated and analyzed. OL-1 could absorb on the surface of the shale core to form a membrane with a micro-nano two-stage roughness, making the surface energy of the core decrease to 0.13 mN/m and the contact angle of the white oil on the core surface increase from 16.39° to 153.03°. Compared with the untreated capillary tube, when immersed into 3# white oil, the capillary tube treated by OL-1 had a reversal of capillary pressure from 273.76 Pa to -297.71 Pa, and the oil imbibition height inside the capillary tube decreased from 31 mm above the external liquid level to 33 mm below the external liquid level. The amount of oil invading into the rock core modified by OL-1 decreased by 64.29% compared with the untreated one. The shale core immersed into the oil-based drilling fluids with 1% OL-1 had a porosity reduction rate of only 4.5%. Compared with the core immersed in the drilling fluids without OL-1, the inherent force of the core treated by 1% OL-1 increased by 24.9%, demonstrating that OL-1 could effectively improve the rock mechanical stability by inhibiting oil phase imbibition.

PDMS/PVDF Electrospinning Membranes for Water-in-Oil Emulsion Separation and UV Protection.

With industry development, the separation of oily wastewater is becoming more critical. Inspired by organisms such as lotus leaves, biomimetic superhydrophobic surfaces with micro-nano structures have shown great potential in this regard. In this work, PDMS/PVDF oil-water separation membranes with designed microstructures were prepared by electrospinning technology. The membrane-forming effect of electrospinning with different ratios of PDMS and PVDF was studied. The study found that membranes with high PDMS content were more likely to form microspheres, and PDMS tended to concentrate on the microspheres. The results also showed that the microspheres would bring better hydrophobicity to the membrane. When the ratio of PDMS to PVDF is 1:2, the membrane has a water contact angle of up to 150° and an oil contact angle of 0°. At this ratio, the separation efficiency of the membrane for the water-in-oil emulsion is 98.7%, and it can still maintain more than 98% after ten separation cycles, which is a good candidate for oil-water separation. Furthermore, microspheres enable the membrane to achieve macroscopic uniformity and microscopic phase separation so that the membranes have both good elongation and fracture strength. In addition, the PDMS/PVDF membranes also exhibit excellent UV resistance, and their UV protection factor is greater than 185, making them a potential UV protective material.

Synthesis of reusable and anti-fouling Co-Al-Ce LDHs coated stainless steel mesh for ultrafast oil/water separation and photocatalytic degradation

Industrial sewage containing oil and dye has already aroused the concerns of cosmopolites. Nowadays, membrane technology is regarded as the spotlight and highly-efficient treatment for various wastewater from human activities. Massive efforts have been put into newly synthesis of low-cost, eco-friendly, low energy consumption, reusable and robust Co-Al-Ce LDHs coated stainless steel mesh (SSM) for wastewater treatment. The CoAlCe-LDHs SSM was fabricated by facile hydrothermal method successfully. While the pristine SSM didn't exhibit selective wettability with water contact angle (WCA) of 114.5°, the novel CoAlCe-LDHs SSM possessed superhydrophilic and underwater superoleophobic property with underwater oil contact angle (UOCA) of 158.5°. The CoAlCe-LDHs SSM was compatibly applied to the separation of oil/water mixtures with highly separation efficiency above 99.5% and ultrafast water flux of 52.2 L·m−2·s−1 under gravity. The easily-fabricated CoAlCe-LDHs SSM was qualified with recyclable, stable and anti-fouling properties, which stayed effective for the separation of oil/water mixtures under at least 30 times recycle and harsh conditions. Moreover, the bifunctional CoAlCe-LDHs SSM also showed excellent photocatalytic activity of dye degradation (with 94.2% degradation of methyl orange solution within 160 min), which can be beneficial to sewage treatment.

Facile approach to fabricate a high-performance superhydrophobic PS/OTS modified SS mesh for oil-water separation

Special wetting materials have been used for the oil and water separation due to their different interfacial attraction of oil and water. Herein, we successfully fabricated superhydrophobic coatings on stainless steel (SS) mesh by depositing successive layers of polystyrene (PS) and octadecyltrichlorosilane (OTS) through the dip-coating method. The as-prepared coating showed a water contact angle (WCA) of 157.5 ± 2°, a rolling angle of 6 ± 2° and an oil contact angle (OCA) of around 0°. The surface microstructure analysis of the coating revealed a regular pattern of microscale bumps with nanoscale folds on it, both of which improve the overall superhydrophobicity of the surface. The capacity of coatings to separate oil and water was examined by employing a variety of mixtures of oil and water, including petrol, diesel, kerosene, vegetable oil, and coconut oil. In case of low viscosity oil, the coated mesh demonstrated separation effectiveness of more than 97% and on the other hand, high viscosity oil demonstrated just 89% efficiency. Low viscosity oils showed a greater permeation flux through the mesh than extremely viscous oil. The mechanical strength of the coating was examined using bending, twisting, adhesive tape testing, sandpaper abrasion tests, and the findings indicated that coated mesh had exceptional mechanical resilience. In addition, the developed superhydrophobic mesh demonstrated excellent thermal stability and self-cleaning properties. Therefore, this superhydrophobic/superoleophilic mesh has a significant deal of application potential in practical.

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.

Surface activity, micellization, and application of nano-surfactants—amphiphilic carbon dots

For nano-surfactants, a new class of surfactants, the unique surface properties, micellization, and application of amphiphilic carbon dots (CDs) have been investigated carefully. Amphiphilic CDs (C12-CDs and C12-SCDs) were synthesized under mild reaction conditions. These CDs exhibit higher surface activity than conventional surfactants (APG12 and SDBS), whereas hydrophilic CDs have negligible surface activity. Above the critical micelle concentration, C12-CDs aggregate into an irregular spherical structure like micelle with an average diameter of about 100 nm, whereas C12-SCDs do not form aggregates. The surface tension of C12-CDs and C12-SCDs reaches the minimum at pH = 3, which is close to the isoelectric point of CDs. As pH increases, the water solubility of CDs increases, and thus the surface tension increases. C12-CDs can still maintain high activity at cNaCl = 250 g/L, but their resistance to CaCl2 is poor. The addition of the sulfonate groups enhances the tolerance of CDs to both NaCl and CaCl2. At cNaCl = 360 g/L and cCaCl2 = 750 g/L, C12-SCDs still have high surface activity.The removal efficiency of oil film and contact angle experiments show that compared to the traditional surfactant SDBS, C12-CDs and C12-SCDs have an excellent wettability alternation due to their abundant hydroxyl, carboxyl, amine, and sulfonate groups. Among them, the wettability alternation of C12-SCDs is better than that of C12-CDs due to their hydrophilic sulfonate groups. Furthermore, the Pickering emulsions stabilized by C12-SCDs have rapid pH and CO2 response performance. In addition, compared to the traditional surfactants SDBS and APG12, CDs have an excellent dispersion performance to MWCNTs. Different from the dispersion mechanism of cationic surfactant CPC (strong electrostatic attraction), CDs are adsorbed on the surface of MWCNTs through their hydrophobic effect and π-π stacking effect to achieve effective dispersion. Among them, because the sulfonate groups have high steric resistance and electrostatic repulsion, the dispersion performance of C12-SCDs is better than that of C12-CDs.

Constructing superhydrophobic sands layer with PTFE nanocoating for desert water storage and oil/water separation

Desert sand is one of the most abundant natural resources, its reutilization is of significance and very valuable for the sustainable development of the environment. In this work, to realize the efficient reutilization of desert sand, we developed a facile method to fabricate superhydrophobic sands based on the self-assembly of PTFE nanocoating. The as-prepared sands exhibit simultaneously superhydrophobic and superoleophilic properties with a water contact angle is ∼150° and an oil contact angle is ∼0°. Besides, the applications of the as-prepared functional sands in water storage and oil/water separation were investigated in detail. The results show that the as-prepared sands exhibit good water storage capacity compared with the raw desert sand. Additionally, the as-prepared sand layer used as an adsorbent or filter can efficiently separate both light and heavy oil/water mixtures with a separation efficiency of > 96% and separation flux of > ∼24000 L/m2h. This work provides a good alternative for achieving the reutilization of desert sand and other natural resources.

Pre-wetting of sand for high speed oil-water separation

The search for a simple, affordable, and rapid separation method for oil-water mixtures is one of the most serious challenges that the world is facing today. Superhydrophobic, or superoleophilic, materials and surfaces are promising choices for these types of separations. In the present study, a high speed gravity-driven oil–water separation method has been realized by using pre-wetting of river sand, sea sand, and desert sand. The superoleophobicity properties of these pre-wetted sand materials have been found to be good, with a maximum oil contact angle of about 141.1° for desert sand and a minimum oil contact angel of 113.8° for sea sand. Also, the relationship between the porosity of the respective sand type and the water phase separation rate was, for the first time, obtained by using the LBM Shan-Chen model and micro-CT characterization. As a result of a simple particle size screening, the highest kerosene-water separation rate for sea sand was 24.3 ± 2.4 mm/s. In fact, this is the highest oil-water separation rate that has ever been achieved for a sand material. In addition to the effect of sand particle size, other factors affecting the rate of oil-water separation (such as number of separation cycles, thickness of sand layer, temperature, pH value, salt concentration, and different oil-water mixtures) have also been investigated.

A superhydrophobic pulp/cellulose nanofiber (CNF) membrane via coating ZnO suspensions for multifunctional applications

Bio-based membranes for removing organic dye and microorganism-containing complicated oil-water effluents simultaneously are sustainable, low-cost, renewable, biodegradable, and nontoxic. Here, a robust, sustainable and molecular-level superhydrophobic Pulp/cellulose nanofiber (CNF) composite membrane (SPCCM) via crosslinking of nanofibers and coating ZnO suspensions for accomplishing this purpose is proposed. The results show that this designed SPCCM has superior superhydrophobicity (water contact angle: 163 ± 2°) and superoleophilicity (oil contact angle: 0 °), which has a great separation efficiency for separating oil-water mixture (92 %) and a high flux (1435 L·m−2·h−1·bar−1). Moreover, SPCCM showed good durability in harsh environment (such as: bending, corrosion solution, temperature, etc). It also showed that the synergistic impact of electrostatic adsorption and ZnO photocatalyst is responsible for the high degradation capacity (Degradation under visible light using 300 w xenon lamp, high degradation efficiency up to 98 %). Furthermore, the SPCCM had a high level of anti-biofouling for microorganisms. Thus, the SPCCM mainly derived from sustainable pulp fibers showed potential performance for oil/water separation and water purification.

Omniphobic carbon steel surface with good wax-repellent performance

In this report, superhydrophobic and omniphobic coatings were produced by a combination of creating a ZnO micro/nanostructure on the carbon steel surface and coating a low surface energy material. Before reducing the surface energy with 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, the steel surface was electrodeposited by a micro/nanostructured ZnO layer for a controlled deposition time. The process resulted in the steel surfaces being superhydrophobic (contact angle of 165 ± 2o) and omniphobic with white oil, diesel oil (contact angle of 135 ± 2o) and paraffin (contact angle of 127 ± 2o). The properties of superhydrophobic/omniphobic steel surfaces were then fully analysed by SEM, XRD, FTIR and contact angle measurements.

Sustainable nanocomposite coating for moulded pulp with enhanced barrier properties for food packaging applications

AbstractDue to poor barrier properties and high sensitivity to moisture, the applications of paper‐based food packaging remain limited. While gaining high barrier performance and surface durability, laminating papers with binders and other materials often leads to reduced recyclability and sustainability. Herein, we present a promising approach to improve the barrier properties and surface oil resistance of bagasse moulded pulp while preserving its green profile. A bio‐nanocomposite layer, combining nanocellulose and shellac (natural polyester), was coated on the surface of moulded pulp. This nanocomposite coating layer provides excellent gas barrier and water barrier performance simultaneously, thanks to the ester modification of nanocellulose to improve its hydrophobicity. With a good compatibility and dispersion in the shellac matrix phase, the modified nanofibrillated cellulose demonstrated an improved barrier performance compared with the unmodified nanofibrillated cellulose. Oxygen transmission rate and water vapour transmission rate of the coated pulps were in the range 60–300 cm3 m−2 day−1 and 10–30 g m−2 day−1, respectively, comparable to those of conventional food packaging materials. The surface resistance of the coated pulps was also greatly improved, indicated by the water contact angle, oil contact angle, Kit test and oil resistance test in a bowl model. The nanocomposite was able to enhance the tensile strength of the moulded pulp by 23%. In summary, the current sustainable nanocomposite coating layer demonstrated great potential in converting paper‐based materials to high barrier and sustainable food packaging. © 2022 Society of Industrial Chemistry.

Synthesis and Optimization of Superhydrophilic-Superoleophobic Chitosan-Silica/HNT Nanocomposite Coating for Oil-Water Separation Using Response Surface Methodology.

In this current study, facile, one-pot synthesis of functionalised nanocomposite coating with simultaneous hydrophilic and oleophobic properties was successfully achieved via the sol–gel technique. The synthesis of this nanocomposite coating aims to develop a highly efficient, simultaneously oleophobic-hydrophilic coating intended for polymer membranes to spontaneously separate oil-in-water emulsions, therefore, mitigating the fouling issue posed by an unmodified polymer membrane. The simultaneous hydrophilicity-oleophobicity of the nanocoating can be applied onto an existing membrane to improve their capability to spontaneously separate oil-in-water substances in the treatment of oily wastewater using little to no energy and being environmentally friendly. The synthesis of hybrid chitosan–silica (CTS-Si)/halloysite nanotube (HNT) nanocomposite coating using the sol–gel method was presented, and the resultant coating was characterised using FTIR, XPS, XRD, NMR, BET, Zeta Potential, and TGA. The wettability of the nanocomposite coating was evaluated in terms of water and oil contact angle, in which it was coated onto a polymer substrate. The coating was optimised in terms of oil and water contact angle using Response Surface Modification (RSM) with Central Composite Design (CCD) theory. The XPS results revealed the successful grafting of organosilanes groups of HNT onto the CTS-Si denoted by a wide band between 102.6–103.7 eV at Si2p. FTIR spectrum presented significant peaks at 3621 cm−1; 1013 cm−1 was attributed to chitosan, and 787 cm−1 signified the stretching of Si-O-Si on HNT. 29Si, 27Al, and 13H NMR spectroscopy confirmed the extensive modification of the particle’s shells with chitosan–silica hybrid covalently linked to the halloysite nanotube domains. The morphological analysis via FESEM resulted in the surface morphology that indicates improved wettability of the nanocomposite. The resultant colloids have a high colloid stability of 19.3 mV and electrophoretic mobility of 0.1904 µmcm/Vs. The coating recorded high hydrophilicity with amplified oleophobic properties depicted by a low water contact angle (WCA) of 11° and high oil contact angle (OCA) of 171.3°. The optimisation results via RSM suggested that the optimised sol pH and nanoparticle loadings were pH 7.0 and 1.05 wt%, respectively, yielding 95% desirability for high oil contact angle and low water contact angle.

Underwater oleophobic-super hydrophilic strontium-MOF for efficient oil/water separation

The oil spill clean-up from water bodies is a major challenge in recent years because of the rise in pollution due to human activities. To tackle these environmental issues, we report the use of the Strontium Metal-Organic Framework (Sr-MOF) for the application of oil–water separation. Herein, the separation is carried out through underwater oleophobic-super hydrophilic properties of the MOF. The Sr-MOF was successfully synthesized using a strontium metal source ([Sr(NO3)2]) and 1,4-benzenedicarboxylic acid (H2BDC) as the organic linker. The MOF showed an excellent separation efficacy of different oils with above 99 % oil rejection driven by gravity. Also, the underwater oil contact angle (UWOCA) of various oils was greater than 132° for Sr-MOF which obeys Cassie-Baxter's theory, due to which the MOF showed excellent oil separation. Interestingly, the flux was dependent on the kind of material the MOF is placed over i.e., for cotton bedding, the flux is above 500 Lm−2h−1 and for steel mesh bedding the flux is above 5000 Lm−2h−1. We have also demonstrated their reusability tests with the least number of 20 cycles which shows a constant rejection of oils. Due to the super-wetting properties, the MOF is stable through several cycles indicating that the Sr-MOF possesses an excellent potential for separating an oil–water mixture. This unique feature of Sr-MOF provides an interesting platform for the applications of MOFs for oil–water separation applications.

Fabrication of superhydrophilic/underwater superoleophobic functionalized-nanoparticles/PVDF-supported thin film composite polyamide membranes for efficient water purification

For water treatment, membrane-based separation methods are very essential owing to long-term efficiency, high mechanical stability and durability. The filtration process with polymer-inorganic and organic composite is an outstanding strategy that enhances the properties of both inorganic materials such as thermal and mechanical stability and organic material including flexibility and processability of the membranes. Therefore, the surface wettability of the membranes is vital for pollutants separation. Here, the high hydrophobic behavior of polyvinylidene fluoride (PVDF) membranes is altered to superhydrophilicity and underwater superoleophobicity via single-step coating. This PVDF membrane has high molecular separation due to the ultrathin thickness and good controllable interlayer. In this study, the PVDF membrane was by interfacial polymerization coated with a polyamide (PAm) layer, modified alumina nanoparticles (Al-NPs), (aminopropyl)triethoxysilane (APTES), and folic acid (FA) through a chemical grafting reaction. The influence of the PAm and Al-APTES-FA content on the morphology, structure, antifouling, and superhydrophilicity of the PVDF-g-PAm@Al-APTES-FA membrane has been investigated which has enhanced the oil and salt rejection as well as filtration performance. Fourier Transform Infrared (FTIR) spectroscopy showed the specific functional groups from the obtained results indicating the successful preparation. Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX), and AFM (Atomic Force Microscope) techniques were conducted to observe the membrane surface morphology, roughness, and elemental adsorption after the filtration process. Furthermore, this modified PVDF membrane exhibited an excellent superoleophobicity with underwater oil contact angle (OCA~145°), and superhydrophilic visualization with water contact angle (WCA ~ 0°) after being functionalized. Additionally, the parameters of membrane performance such as permeate flux, heavy metal ions, oil and salts rejection, were assessed. The modified material on the PVDF membrane enhanced the membrane efficiency under high operating pressure of 10 bar with 53 LMH (L.m−2 h−1, while it is ≈0 for PVDF membrane), permeate flux, over 90 % salt rejection, and almost 100 % hydrocarbons and heavy metal ions rejection, owing to membrane surface changes, hydrophilicity, and roughness. This research will provide new insights on porous surface transformation to improve the separation and antifouling properties of PVDF membranes used in water purification.

Superhydrophobic and Superlipophilic Low Density Polyethylene/Styrene–Butadiene Rubber Thermoplastic Vulcanizate Film for Pressure‐Responsive Continuous Oil–Water Separation

AbstractIn recent years, with the continuous discharge of wastewater, which has caused serious environmental pollution, it is a task to separate oil or water from wastewater. Therefore, an efficient and low‐cost oil–water separation method is needed to separate the oil–water mixture. Here, a superhydrophobic/superoleophilic low density polyethylene/styrene‐butadiene rubber (LDPE/SBR) thermoplastic vulcanizate (TPV) film (oil contact angle of 0° and water contact angle of 161.1° ± 1.7°) is prepared using an etched aluminum foil as a template and applied to a laboratory‐assembled oil–water separation device, which is a new method for oil–water separation via a pressure response valve. The LDPE/SBR TPV film is rolled up and stuffed into the through‐valve, and the gap between the films is used as the pressure response channel for oil and water separation, thus achieving oil and water separation. When the film gap is 25 or 50 µm, the separation efficiency of TPV film is greater than 99% with the variation of external pumping force, indicating that this method can achieve complete oil–water separation under a suitable external pumping force. This functional TPV film has good recyclability, environmental stability, chemical stability, mechanical durability, as well as thermal stability, which makes it have great application potential.

Transforming hydrophobicity of high-density polyethylene surface to hydrophilicity and superoleophobicity by surface grafted with polyvinyl alcohols for oil contaminants cleanup

High-density Polyethylene (HDPE) is widely used in industrial processes due to its excellent mechanical properties, solvent resistance and chemical stability. However, its surface usually shows high hydrophobicity and lipophilicity, which makes it ineffective in resisting contamination by oil pollution. In this study, Polyvinyl alcohols (PVA) were grafted onto the surface of the glycidyl methacrylate (GMA) grafted HDPE to improve the surface hydrophilization, furthermore, the surface structure of the PVA@GMA-HDPE and the factors affecting its hydrophilic modification were investigated. The introduction of the GMA in HDPE surface results in a large number of reactive sites on the inert surface of HDPE, which allows for further grafting of PVA onto the HDPE surface. Most importantly, the addition of PVA improves the water wettability, which reduced the water contact angle from 87.82° to 23.33° in the air and increased the oil contact angle from 107.30° to 156.90° under water. With the help of the significant improvements in resistance to oil contamination, the grease on the surface of the modified HDPE can be easily removed by washing with water after many repetitions. The low cost, simple manufacture and versatility of the PVA@GMA-HDPE with superior hydrophilicity and submerged superoleophobicity have significant application value for sewerage pipes and membranes.

One-step rapid co-deposition of oxidant induced mussel-polyphenol coating on PVDF substrate for separating oily water

Inspired by mussels and plant polyphenols, surface-coated membranes for oil-in-water emulsion separation have attracted extensive attention recently. Here, a one-step rapid co-deposition strategy was proposed to fabricate membranes for separating oily water by oxidation reaction of tannic acid and polydopamine. The polyphenol cross-linked network was formed and quickly co-deposited on the surface of polyvinylidene difluoride (PVDF) membrane. The developed hydrophilic membrane was able to efficiently separate different oil-in-water emulsions. FTIR-ATR, XPS and SEM characterization methods were used to investigate the chemical composition and surface morphology of the modified membranes. Water contact angle, underwater oil contact angle, emulsion permeability, and oil rejection were measured. The experimental results showed that the permeability of pure water and the isooctane-in-water emulsion using PVDF-0.1/0.4/0.2 membrane were 15,713 L∙m−2∙h−1∙bar−1 and 14,552 L∙m−2∙h−1∙bar−1, respectively. The oil rejection reached 99.3%. After five cycles, the initial permeability and the oil rejection were 12,849 L∙m−2∙h−1∙bar−1 and 98.6%, respectively. The developed PVDF-0.1/0.4/0.2 membrane still maintained excellent underwater oleophobicity after being treated in acid, base and salt solutions for 30 days. Furthermore, the time for membrane fabrication was shortened to only 1 h. The proposed membrane modification strategy would have potential application prospects in the efficient separation of oily wastewater.