Oil Adhesion Research Articles

The Tethered Fibrillar Hydrogels Brushes for Underwater Antifouling

The development of antifouling surfaces to prevent bioattachment is an urgent demand for marine coating and biomedical applications. In this paper, two types of anionic and zwitterionic gel fibers are synthesized based on anodic aluminum oxide (AAO) substrate and their antifouling properties against oil and algal attachment are systematically investigated. To begin with, gel surfaces exhibit underwater superoleophoic property and extremely low oil adhesion. The effect of electrolyte on underwater wetting behavior is studied. It is shown that the adhesion of oil droplets on gel fibers significantly increase upon immersing in electrolyte solutions and ionic surfactants, which could be attributed to electrostatic screening effect of salt solution and ion‐pairing interaction. Notably, in regard to Dunaliella tertiolecta and Navicula sp., almost 90% and 95% decrease of fouling algae density are achieved for P(AA/SPMA) and P(AA/SBMA) gel fibers, respectively, comparing with AAO substrate for control. The excellent antifouling property and high structural stability of gel fibers make them effective antifouling surfaces.

A flexible, robust and antifouling asymmetric membrane based on ultra-long ceramic/polymeric fibers for high-efficiency separation of oil/water emulsions.

Polymeric and ceramic asymmetric membranes have dominated commercial membranes for water treatment. However, polymeric membranes are prone to becoming fouled, while ceramic membranes are mechanically fragile. Here, we report a novel concept to develop asymmetric membranes based on ultra-long ceramic/polymeric fibers, with the combined merits of good mechanical stability, excellent fouling resistance and high oil/water selectivity, in order to meet the stringent requirements for practical oil/water separation. The ultra-long dimensions of ceramic nanofibers/polymeric microfibers endow this novel membrane with mechanical flexibility and robustness, due to the integrated and intertwined structure. This membrane is capable of separating oil/water emulsions with high oil-separation efficiency (99.9%), thanks to its nanoporous selective layer made of ceramic nanofibers. Further, this membrane also displays superior antifouling properties due to its underwater superoleophobicity and ultra-low oil adhesion of the ceramic-based selective layer. This membrane exhibits high water permeation flux (6.8 × 104 L m-2 h-1 bar-1) at low operation pressures, which is attributed to its 3-dimensional (3D) interconnected fiber-based structure throughout the membrane. In addition, the facile fabrication process and inexpensive materials required for this membrane suggest its significant potential for industrial applications.

The impact of low-surface-energy functional groups on oil fouling resistance in membrane distillation

Recent progress in developing anti-fouling membranes suggests that integrating low-surface-energy functional groups into a hydrophilic matrix can generate a robust fouling resistant surface that not only mitigates the attachment, but also facilitates the detachment, of hydrophobic foulants. Excellent anti-fouling performance with such surfaces with heterogeneous surface energy has been reported in pressurized membrane processes. However, the impact of low-surface-energy functional groups on the membrane fouling resistance in membrane distillation (MD) has not been investigated and is the goal of the current study. In this study, we compared the fouling behaviors between a reference hydrophobic polyvinylidene fluoride (PVDF) membrane and three composite membranes with chitosan based hydrogel surface but different amount of perfluoroalkyl functional groups. We first fabricated and characterized the three composite membranes, then challenged them in MD experiments with a crude-oil-emulsion as the feed solutions, and finally conducted force spectroscopy to probe the interaction between an oil droplet and the three composite membranes as well as the reference PVDF membrane. The results from MD fouling tests and force spectroscopy suggest that incorporating perfluoroalkyl functional groups into the hydrogel matrix did significantly improve the anti-fouling performance and reduce oil adhesion onto the membrane surface as long as they were not excessive on the surface.

Adhesion and cleaning of foods with complex structure: Effect of oil content and fluoropolymer coating characteristics on the detachment of cake from baking surfaces

The effect of surface coating on the detachment of a complex microstructured food material, was investigated using an improved version of the millimanipulation device described by Ali et al. (2015 Food & Bioproducts Processing, Vol. 93, 256–268). The test material was baked sponge cake batter, which contains approximately 27 vol% bubbles in a ‘continuous’ phase of emulsified oil in a flour/syrup suspension. Detachment in the dry state was studied for aluminium, 304 stainless steel and seven different fluoropolymer coatings. The surfaces differed in surface energy and roughness. The shear force required to detach baked cake, the work done, and the mass of residue remaining on the surface were measured. Virtually all samples detached by cohesive or mixed failure, where adhesion to the surface was stronger than or comparable with cohesive interactions within the cake. The shear force was almost independent of surface composition, energy and roughness, but strongly related to the oil content of the cake. The mass of residue was found to be linearly dependent on the calculated work of adhesion of oil to the surface in an aqueous environment. The quantitative findings are consistent with confocal microscopy images of uncooked batter contacting polar and non-polar surfaces which show very different oil spreading behaviour at the batter-substrate interface. The ability of oil to replace water from a surface is shown to be a key factor determining adhesion of these materials.

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.

Development of electrically conductive-superoleophobic micropillars for reducing surface adhesion of oil at low temperatures

Electrically conductive and superoleophobic micropillars have been developed through the construction of biomimetic micropillars using Ag-filled epoxy composites and the incorporation of FDTS on the micropillar surface. These micropillars are found to be superoleophobic with an oil contact angle of 140°, demonstrating excellent self-cleaning properties. The conductivity of micropillars allows for the Joule-heating effect to actively reduce the adhesion and even unfreeze the frozen oil droplets by passing electrical current. Electrical resistance of the composite micropillars was modulated by two orders of magnitudes by varying the contents of Ag flakes from 45wt% to 65wt%. The effectiveness of conductive micropillars for surface un-freezing was investigated by applying DC current to decrease the adhesion strength of frozen oil droplets on surfaces. The results showed a pronounced reduction of frozen oil adhesion force by 60% when the resistance increased from 7.5Ω to 877Ω after applying DC current for 2min. By continuously applying DC current for 3min, the frozen oil adhesion decreased to 0.05N, reaching zero when the surface was heated up to −10°C after applying DC current for 5min. In contrast, when the droplet was heated up to −5°C by hot air, there is still a substantial force of adhesion. The research findings demonstrate the use of constructing conductive-superoleophobic composite micropillars at surface for eliminating the frozen oil from surfaces at low temperatures.

Oleophobicity of Chitosan/Micron-alumina-Coated Stainless Steel Mesh for Oil/Water Separation

In this research, stainless steel meshes coated with chitosan and micron-alumina were prepared via a dip-coating method. The coated mesh exhibits underwater oleophobic property with low oil adhesion. The influence of different concentrations of chitosan and micron-alumina on underwater oil contact angle of the coated mesh was studied. The separation efficiencies of the coated mesh for different oil–water mixtures were also tested. The results showed that the underwater oil contact angle of the coated mesh was as high as 146° when the concentrations of chitosan and micron-alumina were 0.4 and 0.04 wt%, respectively. The coated mesh can separate different kinds of oil with an efficiency over 90 % in gravity-driven method. Furthermore, the mesh has high recyclability in the application of oil–water separations in both NaCl and weak alkaline solutions. The chitosan and micron-alumina coated mesh has potential applications in oil–water separations.

Alkaline-induced superhydrophilic/underwater superoleophobic polyacrylonitrile membranes with ultralow oil-adhesion for high-efficient oil/water separation

Traditional polymer membranes prepared by phase inversion process have the problems of low flux and serious fouling when they were used for oil/water separation. In this work, an alkaline-induced phase inversion process is developed for the superhydrophilic/underwater superoleophobic polyacrylonitrile (PAN) ultrafiltration membrane. The as-prepared PAN ultrafiltration membrane could effectively separate oil-in-H2O emulsions with a high flux up to 2270L/m2hbar and an extremely high rejection while the oil residual in filtrate after one-time separation is lower than 10ppm. Also, the PAN membrane showed ultralow oil adhesion and antifouling properties and can be easily recycled with flux recovery ratio of 85%. This new PAN membrane has a great potential for treating oily wastewater.

A portable electronic system for in-situ measurements of oil concentration in MetalWorking fluids

MetalWorking fluids (MWFs) are widely used to cool and lubricate machines and tools. By far, the most common MWFs are oil-in-water emulsions with oil concentration (Coil) in the range from 1% to 10%, depending on type of oil, material to be worked, etc. In order to optimize emulsion and machine performance, as well as for good waste policy, the right value of Coil should be kept (approximately) constant during the MWF’s lifecycle to compensate inevitable changes due to water evaporation, bacterial attack, oil adhesion to metal parts, etc. This, however, requires periodic measurements, often skipped because they require unhandy operations and produce inaccurate results. In this context, a new system is presented that is based on the falling ball principle, normally used for viscosity measurements, shown to be suitable also for accurate Coil measurements. In our system, the transit time of the sphere within the instrument is determined by means of inductive proximity sensors, a PT100 sensor is used for temperature whose effects on Coil are accounted for by means of an ad-hoc algorithm. A battery-operated electronic board has been designed that allows rapid and user-friendly “in-situ” measurements and a prototype of an whole portable and automatic instrument, suitable for in-situ measurements, has been fabricated.

The dynamic spreading of nanofluids on solid surfaces – Role of the nanofilm structural disjoining pressure

Nanofluids comprising nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of an aqueous film containing nanoparticles displacing an oil droplet has clearly revealed that the structural disjoining pressure arises due to the layering of the nanoparticles normal to the confining plane of the film with the wedge profile. The pressure drives the nanofluid in the wedge film and the nanofluid spreads. We observed two distinct contact lines: the inner contact line, where the structural disjoining pressure dominates the Laplace capillary pressure, and the outer contact line, given by the Laplace equation prediction extrapolated to the solid substrate where the structural disjoining pressure contribution is negligible. We report here our results of the effects of several parameters, such as the nanoparticle concentration, liquid salinity, temperature, and the substrate contact angle, on the motion of the two contact lines and their effects on the detachment of the oil droplet. We also studied the equilibrated and non-equilibrated oil/nanofluid phases, the time of adhesion of the oil droplet on the solid substrate and the drying time of the substrate. We employed the frictional model to predict the outer contact line velocity and our previous theoretical model (based on the structural disjoining pressure) to predict the inner contact line velocity. The theoretical predictions agreed quite well with the experimentally measured values of the velocities.Our experimental results showed that the motion of the inner contact line was accelerated by the increase in the nanoparticle concentration, temperature, and hydrophilicity of the substrate for the pre-equilibrated oil/nanofluid phases, which resulted in the faster detachment of the oil droplet. The speed of the two contact lines decreased upon the increase in the drying time of the substrate and the oil adhesion time on the substrate.The present results provide new insights into the complex spreading behavior of nanofluids on solid substrates.

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.

Oleophobicity of Biomimetic Micropatterned Surface and Its Effect on the Adhesion of Frozen Oil.

The relationship between the oleophobicity of micropatterned surfaces and the reduction of oil adhesion at low temperatures was explored by using siloxane elastomer surfaces as a model system. Polydimethylsiloxane (PDMS) surfaces were fabricated with varying oleophobicity from oleophilic to superoleophobic by combing the blending of trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FDTS) into PDMS with the construction of bioinspired micropillars. The oil contact angles of micropillars were >130°, with the largest contact angle measured to be 146°. The micropillared surface showed remarkable self-cleaning properties; the contact angle hysteresis was <15°. The transparent oil droplets on PDMS surfaces of varied oleophobicity were frozen into a white-colored solid at -25 °C with the aid of a cooling system. Adhesion forces of the frozen oil droplets were obtained from the knock-off tests, showing that the adhesion forces dropped with the increased oleophobicity. The largest adhesion force was observed on the oleophilic flat surface, while the lowest adhesion force was on the highest oleophobic micropillared surface. The relative effectiveness of chemical and physical modifications on adhesion strength reduction was studied in terms of FDTS and micropillars, respectively. The results showed that a reduction of adhesion strength by 4% was reached by blending FDTS into flat PDMS, while a much more pronounced reduction of frozen oil adhesion strength by 60% was achieved by blending FDTS into PDMS micropillars; these results suggested a possible synergic effect of the FDTS chemistry and micropillar on the reduction of adhesion strength of frozen oil droplets.

Potential application of oil-suspended particulate matter aggregates (OSA) on the remediation of reflective beaches impacted by petroleum: a mesocosm simulation.

This paper presents the oil-suspended particulate matter aggregate (OSA) resulted from the interaction of droplets of dispersed oil in a water column and particulate matter. This structure reduces the adhesion of oil on solid surfaces, promotes dispersion, and may accelerate degradation processes. The effects of the addition of fine sediments (clay + silt) on the formation of OSA, their impact on the dispersion and degradation of the oil, and their potential use in recovering reflective sandy beaches were evaluated in a mesoscale simulation model. Two simulations were performed (21days), in the absence and presence of fine sediments, with four units in each simulation using oil from the Recôncavo Basin. The results showed that the use of fine sediment increased the dispersion of the oil in the water column up to four times in relation to the sandy sediment. There was no evidence of the transport of hydrocarbons in bottom sediments associated with fine sediments that would have accelerated the dispersion and degradation rates of the oil. Most of the OSA that formed in this process remained in the water column, where the degradation processes were more effective. Over the 21days of simulation, we observed a 40% reduction on average of the levels of saturated hydrocarbons staining the surface oil.

PH-Manipulated Underwater-Oil Adhesion Wettability Behavior on the Micro/Nanoscale Semicircular Structure and Related Thermodynamic Analysis.

Controlling oil of wettability behavior in response to the underwater out stimulation has shown promising applications in understanding and designing novel micro- or nanofluidic devices. In this article, the pH-manipulated underwater-oil adhesion wetting phenomenon and superoleophobicity on the micro- and nanotexture copper mesh films (CMF) were investigated. It should be noted that the surface exhibits underwater superoleophobicity under different pH values of the solution; however, the underwater-oil adhesion behavior on the surface is dramatically influenced by the pH value of the solution. On the basis of the thermodynamic analysis, a plausible mechanism to explain the pH-controllable underwater-oil adhesion and superoleophobic wetting behavior observed on a micro- and nanoscale semicircular structure has been revealed. Furthermore, variation of chemistry (intrinsic oil contact angle (OCA)) of the responsive surface that due to the carboxylic acid groups is protonated or deprotonated by the acidic or basic solution on free energy (FE) with its barrier (FEB) and equilibrium oil contact angle (EOCA) with it hysteresis (OCAH) are discussed. The result shows that a critical intrinsic OCA on the micro- and nano- semicircular texture is necessary for conversion from the oil Cassie impregnating to oil Cassie wetting state. In a water/oil/solid system, the mechanism reveals that the differences between the underwater OCA and oil adhesive force of the responsive copper mesh film under different pH values of solution are ascribed to the different oil wetting state that results from combining the changing intrinsic OCA and micro-/nanosemicircular structures. These results are well in agreement with the experiment.

Camelina oil derivatives and adhesion properties

Camelina (Cannabis sativa) is an emerging low-input and stress-tolerant non-food oilseed feedstock in the USA. The seed contains 36–47% oil with 90% unsaturated fatty acids, which means it may be suitable for making oleochemicals and biopolymers. This paper describes the synthesis of several oleo derivatives from camelina oil (CO) and the development of polymers through UV polymerization for pressure-sensitive adhesive (PSA) applications. CO was converted into epoxidized camelina oil, then to partially acrylated epoxidized camelina oil, and finally to di-hydroxyl acrylated epoxidized camelina oil, an acrylic polyol with 1 acrylate functionality and a hydroxyl value of 293mgKOH/g. These oil derivatives were characterized using Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, rheometry, and differential scanning calorimetry. The acrylic polyol was copolymerized with 2-ethylhexyl acrylate (2-EHA) to form tacky viscoelastic polymers. Glass transition temperature of the polymers increased as increasing ratio of acrylic polyol to 2-EHA. A bio-based PSA with a good balance of peel strength (3.86N/in), tack (5.2N/in), and shear resistance (>30,000min) was achieved with equal amounts of acrylic polyol and 2-EHA and a moderate amount of rosin ester added as a tackifier. Frequency sweeps indicated positive correlations between the adhesion performances and viscoelastic responses of PSAs.

The effect of ionic strength on oil adhesion in sandstone--the search for the low salinity mechanism.

Core flood and field tests have demonstrated that decreasing injection water salinity increases oil recovery from sandstone reservoirs. However, the microscopic mechanism behind the effect is still under debate. One hypothesis is that as salinity decreases, expansion of the electrical double layer decreases attraction between organic molecules and pore surfaces. We have developed a method that uses atomic force microscopy (AFM) in chemical force mapping (CFM) mode to explore the relationship between wettability and salinity. We functionalised AFM tips with alkanes and used them to represent tiny nonpolar oil droplets. In repeated measurements, we brought our “oil” close to the surface of sand grains taken from core plugs and we measured the adhesion between the tip and sample. Adhesion was constant in high salinity solutions but below a threshold of 5,000 to 8,000 ppm, adhesion decreased as salinity decreased, rendering the surface less oil wet. The effect was consistent, reproducible and reversible. The threshold for the onset of low salinity response fits remarkably well with observations from core plug experiments and field tests. The results demonstrate that the electric double layer force always contributes at least in part to the low salinity effect, decreasing oil wettability when salinity is low.

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.

Design of honeycomb structure surfaces with controllable oil adhesion underwater

We fabricate honeycomb-like poly acrylic acid (PAA) surfaces and achieve oil adhesion regulation underwater by changing the pore size and the solution pH, which affect triple-phase contact line (TCL) continuity and the negative pressure in the pores.

Polymer porous interfaces with controllable oil adhesion underwater

Porous montmorillonite (MMT)/poly acrylic acid (PAA) composite surfaces with different oil adhesions were achieved by controlling the MMT arrangement in the pore wall.

Ultrafiltration Membranes with Structure‐Optimized Graphene‐Oxide Coatings for Antifouling Oil/Water Separation

Fouling of ultrafiltration (UF) membranes in oil/water separation is a long‐standing issue and a major economic barrier to their use in a broad range of applications. Currently reported membranes typically show severe fouling, resulting from the strong oil adhesion on the membrane surface and/or oil penetration inside the membranes. This greatly degrades their performance and shortens service lifetime. Here, the use of graphene oxide (GO) as a novel coating material for the fabrication of fully recoverable, UF membranes with desired hierarchical surface roughness is accomplished by a facile vacuum filtration method for antifouling oil/water separation. The combination of ultrathin, “water‐locking” GO coatings with the optimized hierarchical surface roughness, provided by the inherent roughness of the porous supports and the corrugation of the GO coatings, minimizes underwater oil adhesion on the membrane surface. Cyclic membrane performance evaluation tests revealed approximately 100% membrane recovery by facile surface water flushing, establishing their excellent easy‐to‐recover capability. The novel GO functional coatings with optimized hierarchical structures may have broad applications in oil‐polluted environments.