Oil Wettability Research Articles

Study on the effect of oligomer silicone surfactant on the properties of drilling fluids

Due to small hole roar, most of low-permeability gas reservoirs are water wetting, and the capillary effect is very prominent, resulting in water blocking damage in the process of exploitation for natural gas. A new kind of oligomer silicone surfactant (OSSF) was developed, and the physical and chemical properties of oligomer silicone surfactant were evaluated. The experimental results indicated that the critical micelle concentration of OSSF was 0.418×10-3 mol/L, and the critical surface tension of OSSF was 20.631 mN/m. OSSF could be adsorbed directionally at the water-rock pore interface, and the cores adsorbed with OSSF should reverse from water wetting to oil wetting or gas wetting. OSSF had good compatibility with sulphonated polymer mud. OSSF could play an important role in unlocking water blocking damage to increase production and efficiency.

Toward the Replacement of Long-Chain Perfluoroalkyl Compounds: Perfluoropolyether-Based Low Surface Energy Grafted Nanocoatings

We describe a straightforward approach to fabricating perfluoropolyether (PFPE)-based nanocoatings, significantly decreasing the spreading of oil and water on coated surfaces. In the fabrication, polyglycidyl methacrylate (PGMA) is used as an anchoring layer deposited on the silicon surface before PFPE attachment. Perfluoropolyether-based polyester acid (PFPE-COOH) is then grafted to the PGMA surface to reduce its surface energy and, consequently, wettability. The grafted surface demonstrates a hexadecane contact angle of 40–46° and a water contact angle of 80–98°. The surface’s wettability strongly depends on the grafted layer thickness, where grafting of the thicker PFPE layers results in lower oil and water wettability. We expect that the employment of PFPE-based grafted nanocoatings will eliminate the health and environmental concerns of long perfluoroalkyls, which are typically used to obtain surfaces with decreased spreading of oil and water.

Synergetic adhesion in highly adaptable bio-inspired adhesive

Biologically inspired adhesives microstructure requires enough flexibility to make a conformal attachment to the surface as well as high rigidity to maintain the mechanical stability of structure against buckling. To tackle these conflicting factors for the synthetic adhesives is a challenge towards large-scale production and utilizing in practical applications. Addressing this problem, we have fabricated a honeycomb structure with a soft elastic film, partially covering the cavity of the honeycomb pattern. Honeycomb structure provides enough support to maintain the structural stability of the microstructure and soft PDMS film over the pattern provides sufficient flexibility to form a strong attachment with the target surface. Meanwhile, the resemblance of the designed structure to the octopi’s sucker generates a negative pressure resulting in suction forces. To justify this suction effect, we compared our results with other controlled honeycomb microstructures (1) without any elastic film (2) with elastic film covering the whole cavity of the honeycomb pattern. Experimental results and theoretical prediction demonstrate the synergistic role of van der Waals and suction forces in the proposed partial-film honeycomb microstructure. The synergistic role of adhesive forces makes this structure a stronger, durable, and surface adaptable adhesive. We also investigated the critical role of the viscous forces for our proposed microstructure in water and silicon oil wetting conditions which signify the contribution of capillary forces.

Silica nanofluid in low salinity seawater containing surfactant and polymer: Oil recovery efficiency, wettability alteration and adsorption studies

Production of crude oil from a matured oil reservoir is challenging due to the low recovery factor. Hybrid methods have demonstrated potential in oil recovery from the matured crude oil reservoir. In recent years, the low salinity water with chemicals (viz., surfactant, polymer) and nanoparticles have brought the attention of the researchers due to their ability in altering the interfacial properties of the rock-oil-water systems favorable for crude oil recovery. The current interest by industries in injection fluid (i.e., low salinity water injection) has prompted the invention of a hybrid oil recovery agent for matured crude oil reservoirs. In the current study, a novel silica-based hybrid nanofluids (NFs) of variable silica nanoparticles (NPs) concentration in low salinity seawater with anionic surfactant (AOT: dioctyl sodium sulfosuccinate) and polymer (PVP–K30: polyvinylpyrrolidone) (sometimes referred to as SMART LowSal) are used as an injection fluid in a sand-pack reactor. Oil recovery from oil saturated sand-pack reactor is observed to enhance due to NFs (hybrid) injection after secondary recovery. The characteristic study of relative permeability curves discloses that sand surface was initially water-wet and converted to strongly water-wet in the presence of NFs. A nuclear magnetic resonance (1H NMR) study reveals that adsorption of the chemical appeared on the sand surfaces, which could be the reason for wettability alteration, and thereby enhanced oil recovery. Similarly, the scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) of the sand samples before and after injection disclosed desorption of hydrocarbon from the sand surfaces after NFs injection. An additional 5–10% oil recovery is achieved after chemical flooding due to the injection of NFs. Adsorption isotherm study well agreed with the monolayer adsorption of surfactant on the sand surface.

Electrically Induced Underwater Superaerophilicity/Superaerophobicity Switching on Polypyrrole-Coated Mesh Films for Selective Bubble Permeation.

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS- ), and becomes underwater superaerophobic as the PFOS- are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices.

A molecular insight into the effect of key ions on the detachment of crude oil from calcite surface: Implication for low salinity water flooding in carbonate reservoirs

The detachment of crude oil from calcite surface plays an important role in oil recovery and wettability alteration during low salinity water flooding in carbonate reservoirs. The effects of brine salinities and key ions on the dynamic detachment process have been much of debate in the past decades in theories and experiments due to complex mechanisms behind the crude oil-calcite interactions. Herein, molecular dynamic simulation was used to study the influence of brine salinities and ion concentrations on the detachment mechanism of crude oil from calcite surface by establishing 20 brine-crude oil-calcite molecular models varying salinities and key ion concentrations in brine. Molecular configurations, concentration distribution profiles, interaction energies, H-bond numbers and center of mass (COM) distances were carefully analyzed to characterize the dynamic crude oil detachment performance. The results reveal that reducing the brine salinities and ion concentrations can significantly weaken the interaction intensity between oil and calcite and accelerate the detachment process. Therefore, the oil detachment is induced and the effect of low salinity on oil detachment process is significantly time-dependent. The concentration distribution profiles shows that the strong polar oil molecules, for example acetic acid molecules, can't be detached from calcite surface by tuning the brine salinity and key ions. The present of Mg2+ and Na+ is able to delay the detachment process of oil molecules and as a consequence, result in the impeded oil detachment process according to time-dependent dynamic molecular configurations, interaction energies and COM distances analysis. Furthermore, the present of Ca2+ is able to strengthen the interaction between oil and calcite and in consequence, hinder the detachment of oil molecules from the calcite surface according to the interaction energy, the molecular configuration and COM distances. This study should provide the molecular-scale insights into wettability alteration and enhanced oil recovery by low salinity water flooding in carbonate reservoirs.

Carbonate oil and gas source rocks wettability alteration due to influence of polymer-colloidal drilling mud

Evaluation of rock wettability is an important task, since this parameter determines the distribution of water and oil in the reservoirs and their relative and phase permeability. The reliability of evaluation the wettability of rock samples depends on the drilling-in conditions during core sampling and core sample preparation methods. The investigation of the surface properties of the core from the Orenburg oil and gas condensate field showed that using of polymer-colloidal drilling mud leads to hydrophilization of the samples' surface. To obtain information on the actual wettability values of rock samples taken from wells drilled with polymer-colloidal drilling mud a method for estimating the relative (predominant) wettability of rocks based on petrophysical and lithological studies data is proposed. The authors suggest that the extraction of oil and gas source rock samples leads to irreversible changes in surface properties that cannot be restored. Keywords: selective wettability; relative wettability; predominant wettability; polymer-colloidal drilling mud; residual gas saturation; trapped gas saturation; pore space structure; extraction.

Microstructural wettability of oil and gas condensate zones of the Karachaganak field

The Karachaganak field is represented by gas condensate and oil zones, a convenient object for studying changes in microstructural wettability during the transition from one zone to another. Microstructural wettability was characterized by a hydrophobization coefficient, Ѳн, which determines the proportion of the pore surface area occupied by adsorbed hydrocarbons. It was found that Ѳн of the samples of the gas and gas condensate zones is the same (on average 0.140), the oil zone - on average 0.250. Analysis of the IR spectra of extracted hydrocarbons showed that the microstructural wettability of the oil zone contains more aromatic, aliphatic, oxidized and sulfur-containing structures and fewer branched structures than in the gas condensate zone. The microstructural wettability of carbonate reservoirs depends on the hydrocarbon composition of the adsorbed oil. Keywords: microstructural wettability; hydrophobic coefficient; hydrocarbons; spectral coefficients.

Numerical simulation of cold and hot water injection into naturally fractured porous media using the extended–FEM and an equivalent continuum model

AbstractIn this paper, a computational technique is presented for the isothermal and non‐isothermal water injection into naturally fractured oil reservoirs. A remarkable number of naturally fractured reservoirs contain relatively heavy oils that could not be extracted economically; hence, the thermal recovery methods are extensively used for such reservoirs. In this study, the effectiveness of hot water injection over cold (isothermal) water injection in oil production is quantified. The influence of long and short fractures and their alignments on oil recovery are discussed. To this end, a 2D model for two‐phase fluid flow and heat transfer is presented. The medium is assumed to be partially saturated with water as the wetting phase and oil as the non‐wetting phase. The governing equations consist of the energy balance equation together with the continuity equations of both fluid phases. To take the long (macro) fractures into account, the extended finite element method is employed by considering permeable fracture faces; accordingly, the mass and heat transfer between the fracture and the matrix are captured accurately. In addition, the network of short (micro) fractures is incorporated by an equivalent continuum model. Several numerical examples are presented to demonstrate the influence of injection temperature, initial reservoir temperature, and the long and short fractures on oil production. Furthermore, the simultaneous effect of the macro‐ and micro‐fractures along with the injection temperature are examined. The results show that the proposed computational model is a promising tool that can be used in the cold or hot water injection, and can be employed in the economic feasibility studies of recovery methods in the future.

Oil-water separation using surface engineered superhydrophobic and superoleophilic membrane for the production of clean water

Oil water separating membranes, exhibiting contrasting wetting characteristics for oil and water (superhydrophobicity, and superoleophility) were fabricated by dip coating different concentrations (5%, 10% and 20%) of trichloro(octadecyl)silane on the micro porous stainless steel mesh. The static contact angles of the fabricated surface in solid-air-water, and solid- air-oil interfaces are found to be ~152° and ~0° respectively. When trichloro(octadecyl)silane coated stainless steel membrane was used as a separating medium in the gravity driven oil water separating system, 99% oil-water separating efficiency was achieved in a single pass, and in addition to this, the fabricated membrane retained its wetting characteristics and oil water separating efficiency, even after 10 consecutive passes of oily water through the membrane. When the oily water comes in contact with the surface of the separating membrane, the water solid interface gets into Cassie-Baxter wetting state, where the air in the micro/nano structured pits renders low affinity of water on the membrane surface, whereas the surface roughness enhances the affinity of oil on the solid surface, and hence the coated surface attracts the oil phase to the pore boundaries of the mesh, and at the same time pushes the water phase to the top. The morphological characteristics and the elemental composition with FE-SEM, EDS, Elemental mapping and XPS characterizations, and the surface wettability of the coated membrane by measuring the interfacial contact angles were also carried out.

Wettability alteration by surface adsorption of asphaltene molecular in carbonate porous media

In this study, the effect of four asphaltene samples on the wettability alteration of carbonate reservoir rock is investigated. The wettability of each core, before and after the deposition of asphaltene, is evaluated using two methods: relative permeability and contact angle. Normally, core samples got oil-wet after the asphaltene deposition, and the contact angle on the surface increased. However, the degree of wettability of each crude oil was different based on the asphaltene composition. According to the elemental analysis of asphaltene samples, the H/C index alone cannot show the asphaltene adsorption potential. The sulfur is an element that enhances asphaltene-asphaltene interaction, but weakens calcite-asphaltene interaction. The oxygen can also enhance the adsorption of asphaltene to calcite, depending on the functional group and its location in the molecule. According to the results of the FTIR spectrum of asphaltene and rock powder, there are three main mechanisms for adsorption of asphaltene to calcite surface, followed by wettability alteration. The first mechanism is the electrostatic interaction between asphaltenes and calcite, which is because of the poly-aromatic nature of asphaltene. The intensity of the electrostatic interaction between asphaltene and rock is directly related to the aromaticity and condensation index of asphaltene. The second mechanism is dispersion, in which the side alkyl chain in the aromatic rings causes asphaltene to be adsorbed into the surface of the rock. The intensity of this mechanism is also proportional to the aliphatic index and the long chain index of asphaltene. The third mechanism, which is less important than the two above-mentioned ones, is the hydrogen bond that is proportional to the ROH index, calculated from the FTIR spectrum. To study the relationship between the electrostatic property of the surface after asphaltene adsorption with surface wettability, zeta potential was used. The results showed that asphaltene, because of its acidic nature, adsorbed to the calcite surface, would make its zeta potential negative. However, more negative zeta potential will not necessarily increase the contact angle. In other words, the surface wettability and electrostatic properties of the surface are two distinct categories that do not have a clear relationship. The surface wettability is more dependent on the amount of aromaticity index of asphaltene, whereas the electrostatic property of the surface is a function of the percentage of oxygen and sulfur compounds in the asphaltene structure. Finally, the scanning electron microscopy (SEM), along with the elemental analysis, was used to investigate the dispersion of various elements at the calcite surface after wettability alteration. The calcium and oxygen are the main elements of calcite production; therefore, the elemental mapping indicated that the surface would be covered with calcium and oxygen prior to the deposition of asphaltene (CaCO3). But by asphaltene deposition on the rock surface, calcium will be observed scattered in some points. For this reason, the amount of calcium in the elemental mapping can be related to the level of surface wettability, so that the lower the percentage of calcium in the surface, the more the asphaltene is adsorbed into calcite, and the changes in the contact angle is greater.

Experimental analysis of oil displacement by hybrid engineered water / chemical EOR approach in carbonates

Fast depletion in oil reserves has steered the petroleum industry towards developing novel enhanced oil recovery (EOR) techniques. The standalone EOR methods have associated merits and demerits. For example, the chemical EOR (CEOR) methods have very limited applications in high salinity, high temperature carbonate reservoirs because of increased chemical adsorption and high project costs. In this study, hybrid approaches utilizing engineered water (EW) and CEOR were investigated for carbonate reservoirs. The synergetic effects of EW and chemicals such as polymer, alkali, and surfactant were analyzed. Phase behavior analysis, aqueous stability study, surfactant static adsorption test, and polymer rheological characterization were conducted to select the optimum alkali/surfactant/polymer formulation. To evaluate the increase in oil recovery, wettability alteration, and extent of mobility control, various EW/CEOR combinations were designed for oil displacement experiments, including EW/surfactant flooding (EWSF), EW/polymer flooding (EWPF), EW/surfactant/polymer flooding (EWSPF), and EW/alkali/surfactant/polymer (EWASP) flooding. The EWASP flooding was executed in both continuous and slug-wise injection modes, and the best hybrid EW/CEOR design was selected. 10 times diluted Caspian seawater spiked with optimized active ions was used as the EW. Based on phase behavior and static adsorption tests, 1 wt% Soloterra 113-H was used as a surfactant, while 1 wt% sodium carbonate was used as an alkali. Flopaam 5115 was employed as a polymer with an optimum concentration of 1500 ppm, as established from rheological experiments. The best combination in terms of oil recovery, stability of polymer and surfactant, and chemical consumption was the hybrid EWASP flooding in slug-wise injection mode. This injection scheme resulted in 36% OOIP incremental recovery, 7% higher than the EWPF and EWSPF scenarios and 3% higher than hybrid EWASP flooding in continuous injection mode. Hybrid designs proved to be more effective in recovering residual oil because of better mobility control, reduced capillary trapping, wettability modification, lower surfactant adsorption, and ultra-low interfacial tension (IFT). Our studies showed that the application of hybrid EW/CEOR for carbonate formations, as a novel approach, can expand the application envelope of chemical methods to challenging carbonate formations by making the EOR projects technically and economically viable.

One-step fabrication of biodegradable superhydrophobic PLA fabric for continuous oil/water separation

Various types of functional materials incorporating superhydrophobic components have been rapidly developed for efficient oil/water separation. The post-processing of these used separated materials remains a challenging problem due to their non-biodegradable characteristics in natural environments, thus easily contributing to secondary contamination. Herein, we report a biodegradable superhydrophobic PLA fabric with hierarchical coral-like micro/nano structures by a one-step spraying method. The as-prepared PLA fabric was found to be both superhydrophobic and superoleophilic with a static water contact angle of 161 ± 2° and an oil contact angle of 0°. In addition, the as-prepared PLA nonwoven fabrics also revealed efficient continuous oil separation efficiency (>97.5%) and tiny water droplet collection efficiency, as well as high oil flux ranging from 2239 L·m−2·h−1 to 59,713 L·m−2·h−1. Furthermore, these fabrics retained their inherent wetting property and oil separation ability in a variety of acidic and basic solutions, 3.5 wt% NaCl solution, hot (100 °C), and freezing (0 °C) temperatures. This study provides a novel and environmentally friendly method for preparing biodegradable oil–water separation materials with green post-treatment characteristics when compared to the non-biodegradable separation materials, indicating potential applications in the fields of green water treatment and petroleum refining.

Interfacial properties and antioxidant capacity of pickering emulsions stabilized by high methoxyl pectin-surfactant-pea protein isolate-curcumin complexes: Impact of different types of surfactants

In the present study, high methoxyl pectin-surfactant-pea protein isolate-curcumin (HMP-surfactant-PPI-Cur) complexes were used as stabilizers for Pickering emulsions. The impact of different types of surfactants in the complexes, including rhamnolipid (Rha), tea saponin (TS) and ethyl lauroyl arginate hydrochloride (LAE), on the interfacial properties and antioxidant capacity of Pickering emulsions was investigated. The pH for the fabrication of complexes with desirable wettability of both aqueous and oil was determined by turbidimetric titration and contact angle measurement. The results showed that the pH of 3.2 was an optimal value to fabricate the complexes. Among these complexes, the HMP-Rha-PPI-Cur complex exhibited the optimal emulsifying property, since it exhibited a relatively low initial interfacial tension of 38.99 mN/m. Moreover, the result of the interfacial tension measurement indicated that the HMP-Rha-PPI-Cur complex could be rapidly adsorbed on droplets, and the adsorbed protein fraction was 99%. Furthermore, after 30 days of storage, the emulsion stabilized by the HMP-Rha-PPI-Cur complex exhibited the lowest serum index of 9.86% and peroxide value of 47.52 mmol/L. In summary, the interfacial properties, stability and antioxidant capacity of emulsions could be more effectively enhanced in the presence of Rha in the complex.

Preparation of polyoxypropylene surfactant-based nanoemulsions using phase inversion composition method and their application in oil recovery

Emulsification using phase inversion composition (PIC) was achieved by changing the composition of surfactants at a constant temperature. The method has great potential to scale up applications due to the ease in the formation of nanoemulsions and the relatively low energy involved. Surfactants containing composition-sensitive polyoxyethylene (POE) chains are widely used to prepare nanoemulsions using the PIC method. It is, therefore, anticipated that surfactants containing composition-sensitive polyoxypropylene (POP) chains can also be used to prepare nanoemulsions using the PIC method. The POP surfactant D230-2OA, containing short POP chains, was obtained from the electrostatic interactions between hydrophilic POP diamine (D230) and hydrophobic oleic acid (OA). The synthesized D230-2OA was used as an emulsifier in the preparation of the n-dodecane-in-water nanoemulsion using the PIC method. The effects of D230-2OA concentration, oil-to-surfactant weight ratio, and NaCl concentration on the droplet size of the nanoemulsions was investigated using dynamic light scattering (DLS). The morphology of the nanoemulsion was characterized using cryogenic transmission electron microscopy (cryo-TEM). The wettability of the crude oil–saturated quartz plate before and after treatment with nanoemulsions was obtained using contact angle measurement. A core flooding experiment demonstrated the efficiency of the diluted nanoemulsion in enhanced oil recovery, with an additional recovery of 21.30%. The nanoemulsion prepared with the POP surfactant as the emulsifier using the PIC method has wide application in petroleum recovery.

Assessment of low salinity waterflooding in carbonate cores: Interfacial viscoelasticity and tuning process efficiency by use of non-ionic surfactant

Hypothesis. A large number of papers discuss merits and mechanisms of low salinity waterflooding. For each mechanism proposed, there are counter examples to invalidate the stated mechanism. The effect of wettability from low salinity water, which is predominantly stated in literature as the dominant mechanism, may not be valid. We introduce a direct correlation between oil-brine interfacial viscoelasticity and oil recovery from waterflooding.Experiments. The oil recovery is investigated in carbonate rocks for three light crude oils, by injection of a wide range of aqueous phases, ranging from deionized water to very high salinity brine of 28 wt%, and low concentration of a non-ionic surfactant at 100 ppm. The oil-brine interfacial viscoelasticity is quantified and supplementary measurements of interfacial tension and wettability are performed.Findings. In our experiments, oil recovery is higher from high salinity water injection than from low salinity water injection. A strong relationship is observed between interface elasticity and oil recovery for different concentrations of salt in the injected brine as well as for ultra-low concentration surfactant. An elastic oil-brine interface results in high oil recovery. The surfactant molecule we have selected prefers the oil–water interface despite high solubility in the oil phase and makes ultra-low concentration of 100 ppm in injection water very effective. Contrary to widespread assertions in the literature, we find no definitive correlation between oil recovery and wettability.

High-hydrophobic ZIF-8@PLA composite aerogel and application for oil-water separation

Herein, a hierarchical porous ZIF-8@PLA composite aerogel was prepared by combining metal–organic skeleton ZIF-8 nanoparticles with polylactic acid (PLA) aerogel matrix by physical blending and thermally induced phase separation with the assistance of water. By changing the ZIF-8 ratio in the aerogel, the pore size, pore surface roughness, and specific surface area of the aerogel can be controlled and adjusted successfully. Compared with pure PLA aerogels, the prepared ZIF-8@PLA aerogels have higher oil wettability and significantly improved mechanical properties. The morphology, wettability, adsorption capacity, circulating oil–water separation capacity, and oil adsorption capacity of the composite aerogels were thoroughly investigated. The results show that ZIF-8@PLA aerogel with 1 wt% ZIF-8 exhibits the highest oil wettability, the largest specific surface area, the highest oil–water separation performance, and good reusability in oil–water separation. The tensile strength and breaking elongation of ZIF-8@PLA aerogel with 1 wt% ZIF-8 are raised to 0.257 MPa and 23%, while those of pure PLA membranes are 0.135 MPa and 13%, respectively. The ZIF-8@PLA aerogel has been proved to be an ideal material for efficient oil–water separation due to the rapid oil wetting capacity, pore roughness, and synergistic adsorption of ZIF-8 porous nanoparticles.

Performance evaluation of silica nanofluid for sand column transport with simultaneous wettability alteration: An approach to environmental issue

The most promising method to improve chemical oil recovery via wettability alteration is associated with colloidal solution such as nanofluid. However, nanofluids show limitations due to nanoparticle agglomeration which may result into pore blockage during its injection in a porous media. The unsuccessful recovery of injected nanoparticles has increased their footprints, which is becoming a serious environmental issue. Therefore, this study reports the use of a co-stabilizer i.e. TiO2 (0.05 and 0.1 wt%) that not only reduces nanoparticle agglomeration in silica nanofluid (SiO2, 0.5 wt%) but also improves its wetting property and oil recovery from synthetic sand-packs of porosity = ∼29–33% and permeability = ∼700–800 mD. In nanofluid synthesis, polymer polyacrylamide was used as base fluid and surfactant [anionic: sodium dodecylsulfate and nonionic: triton x 100] was used to find improvements in wettability alteration, interfacial tension reduction, and oil recovery results of nanofluid. With surfactant, the wetting property of STN (SiO2–TiO2 nanofluid) was found superior (strong water-wet) as confirmed by maximum (67%) reduction in contact angle. Also, interfacial tension of crude oil reduced by ∼91% which increased the chemical oil recovery by ∼78% from sand-pack. Importantly, nanofluid use in porous media is associated with environmental concern. Therefore, each nanofluid was repetitively (3 times) flooded through sand-pack and NP retention was examined using three different characterization methods (contact angle, ultraviolet visible, and field emission scanning electron microscopy) and suitably compared to find least nanoparticle retention in porous media. For surfactant treated nanofluids, nanoparticle retention of 0.03–0.07 wt% was determined while its value was significantly higher (0.31 wt%) for conventional SiO2 nanofluid. Finally, this study suggests that nanoparticle retention of conventional silica nanofluid can be reduced through the selection of a proper co-stabilizer that may help to protect subsurface from pore blockage and other associated environmental issues.

Towards a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellent Perfluoropolyether-Based Polyurethane Oligomers

Original perfluoropolyether (PFPE)-based oligomeric polyurethanes (FOPUs) with different macromolecular architecture were synthesized (in one step) as low-surface-energy materials. It is demonstrated that the oligomers, especially the ones terminated with CF3 moieties, can be employed as safer replacements to long-chain perfluoroalkyl substances/additives. The FOPU macromolecules, when added to an engineering thermoplastic (polyethylene terephthalate, PET) film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. The best performing FOPU/PET films have reached the level of oil wettability and surface energy significantly lower than that of polytetrafluoroethylene, a fully perfluorinated polymer. Specifically, the highest level of the repellency is observed with an oligomeric additive, which was made using aromatic diisocyanate as a comonomer and has CF3 end-group. This semicrystalline oligomer has a glass transition temperature (Tg) well above room temperature, and we associate the superiority of the material in achieving low water and oil wettability with its ability to effectively retain CF3 and CF2 moieties in contact with the test wetting liquids.

Graphene-bentonite supported free-standing, flexible membrane with switchable wettability for selective oil–water separation

In this work, we synthesized a novel, free-standing, flexible sodium-bentonite-fabricated graphene (SBG) composite membrane. The prepared SBG membrane was successfully employed for the selective separation of oil and water. SBG-fabricated filter paper and cotton cloth membranes were easily prepared using simple vacuum filtration and coating methods. The SBG composite membrane exhibited switchable wettability properties, which rendered it capable of switching the surface into either hydrophilic/oleophobic or hydrophobic/oleophilic with the selective treatment of water or oil/organic solvent, respectively. The prepared SBG composite was characterized using X-ray diffraction, thermo-gravimetric analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The as-prepared membrane has high efficiency (>98%) to separate oil–water mixtures, a good recyclability (96% efficiency after 10 cycles), a high flux of 625 Lm−2h−1, and a good oil rejection ratio (>97%). The SBG composite can easily be scaled to separate the oil–water mixture for industrial applications. Furthermore, the advantages of the membrane are its easy preparation, self-cleaning property, switchable wettability property (hydrophilic/oleophobic to hydrophobic/oleophilic and vice versa), high flux and excellent recyclability for the selective separation of oil/organic solvents and water from their mixtures.