Oil-water Interfacial Tension Research Articles

Constructing a viscoelastic film for enhanced oil recovery via self-adsorption of amphiphilic nanosheets at oil-water interface

Immiscible liquid-liquid interfaces have widespread applications in drug delivery, oil-water separation, oil recovery, emulsion and foam stability, etc. Here, a dense viscoelastic interface film is constructed via the self-adsorption of amphiphilic molybdenum disulfide nanosheets at the oil-water interface, which has significant implications for enhanced oil recovery. The microscopic dispersion characteristics of amphiphilic nanosheets in water phase are characterized using Cryo-EM, and the adsorption regularities of amphiphilic nanosheets in horizontal and vertical directions of oil-water interface are also revealed. Besides the mechanical response and rheological properties of interface adsorption film are systematically studied. Experimental results demonstrate that the amphiphilic nanosheet can self-curl to form a single amphiphilic nanosheet with a size of 30 nm in the water phase as the amphiphilic nanosheets concentration is lower than 50 mg/L. When the amphiphilic nanosheets concentration reaches 100 mg/L, obvious water-phase aggregation behaviors happen. The amphiphilic nanosheets can reduce the oil-water interfacial tension from 18.47 mN/m to 0.27 mN/m by forming multilayer adsorption at the oil-water interface. The adsorption ratio of amphiphilic nanosheets from bulk phase to oil-water interface can reach 97.50 %. In addition, the oil-water interface adsorption film exhibits excellent elastic properties and higher strength because the amphiphilic nanosheets can form a planar network structure at the oil-water interface which can be also directly observed in microfluidic pores. The storage modulus and interface shear viscosity of interface adsorption film are 1.65 Pa and 1.38 mN·s/m, respectively. In theory, the required desorption energy of a single amphiphilic nanosheet from oil-water interface to bulk phase is deduced to be 587 KBT. This work is expected to provide amphiphilic molybdenum disulfide nanosheet as an effective candidate for enhanced oil recovery.

Preparation and Performance Evaluation of Amphiphilic Polymers for Enhanced Heavy Oil Recovery.

The continuous growth in global energy and chemical raw material demand has drawn significant attention to the development of heavy oil resources. A primary challenge in heavy oil extraction lies in reducing crude oil viscosity. Alkali-surfactant-polymer (ASP) flooding technology has emerged as an effective method for enhancing heavy oil recovery. However, the chromatographic separation of chemical agents presents a formidable obstacle in heavy oil extraction. To address this challenge, we utilized a free radical polymerization method, employing acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, lauryl acrylate, and benzyl acrylate as raw materials. This approach led to the synthesis of a multifunctional amphiphilic polymer known as PAALB, which we applied to the extraction of heavy oil. The structure of PAALB was meticulously characterized using techniques such as infrared spectroscopy and Nuclear Magnetic Resonance Spectroscopy. To assess the effectiveness of PAALB in reducing heavy oil viscosity and enhancing oil recovery, we conducted a series of tests, including contact angle measurements, interfacial tension assessments, self-emulsification experiments, critical association concentration tests, and sand-packed tube flooding experiments. The research findings indicate that PAALB can reduce oil-water displacement, reduce heavy oil viscosity, and improve swept volume upon injection into the formation. A solution of 5000 mg/L PAALB reduced the contact angle of water droplets on the core surface from 106.55° to 34.95°, shifting the core surface from oil-wet to water-wet, thereby enabling oil-water displacement. Moreover, A solution of 10,000 mg/L PAALB reduced the oil-water interfacial tension to 3.32 × 10-4 mN/m, reaching an ultra-low interfacial tension level, thereby inducing spontaneous emulsification of heavy oil within the formation. Under the condition of an oil-water ratio of 7:3, a solution of 10,000 mg/L PAALB can reduce the viscosity of heavy oil from 14,315 mPa·s to 201 mPa·s via the glass bottle inversion method, with a viscosity reduction rate of 98.60%. In sand-packed tube flooding experiments, under the injection volume of 1.5 PV, PAALB increased the recovery rate by 25.63% compared to traditional hydrolyzed polyacrylamide (HPAM) polymer. The insights derived from this research on amphiphilic polymers hold significant reference value for the development and optimization of chemical flooding strategies aimed at enhancing heavy oil recovery.

Molecular-level study of hydrophobic interactions during low-rank coal particle-bubble attachment

Particle-bubble attachment is a crucial part of coal and mineral flotation processes. The attachment of two different hydrophobic low-rank coal particles to bubble surface were simulated by a non-equilibrium molecular simulation method. Both particles were subjected to water film drainage resistance when approaching the bubble. Eventually, CPC (low-rank Coal Particle with mixed Collector adhered) jumped in and attached to bubble, but CP (low-rank Coal Particle) had only repulsive effect with bubble. The surface water film of CPC generated tiny hole under the entropy effect of water molecule rearrangement, and the presence of gas–water and oil–water interfacial tension promoted the rapid expansion of the hole until the water film rupture. The critical rupture thickness of the water film on CPC surface was about 1 nm and the rupture was completed in a very short time of 0.4 ns. The CPC jumped in and attached to the bubble surface under the action of oil–water interfacial tension. This suggests that the long-range hydrophobic force originates from the combined action of various interfacial tensions. Our results demonstrate the important role of interfacial tension in the attachment of hydrophobic particle to bubble, and contribute to the connection between microscopic and macroscopic mechanism of particle-bubble attachment.

Experimental and model analysis of membrane permeance in cross-flow multi-channel membrane emulsification

Membrane emulsification has many applications in food emulsions, cosmetics, controlled release systems for pharmaceuticals, and the preparation of nanoparticles. Membrane permeance is a key parameter that directly determines the design and processing capacity of the system. However, establishing an accurate model to describe the relationship between membrane permeance and related factors remains challenging. Herein, the variation pattern of membrane permeance in a cross-flow multi-channel membrane emulsification system under emulsifier-free conditions was investigated through experiments and a model. Membrane permeance strongly depended on the membrane pore size, transmembrane pressure, and oil–water interfacial tension. A prediction model of the membrane permeance for the cross-flow multi-channel membrane emulsification process was established based on the empirical model with a relative error of ±10 %. The established model can be used to predict the optimal membrane pore size for a given membrane permeance under different operating conditions.

Complex bio-nanoparticles assembled by a pH-driven method: environmental stress stability and oil-water interfacial behavior.

Protein-based nanoparticles have gained considerable interest in recent years due to their biodegradability, biocompatibility, and functional properties. However, nanoparticles formed from hydrophobic proteins are prone to instability under environmental stress, which restricts their potential applications. It is therefore of great importance to develop green approaches for the fabrication of hydrophobic protein-based nanoparticles and to improve their physicochemical performance. Gliadin/shellac complex nanoparticles (168.87 ~ 403.67 nm) with various gliadin/shellac mass ratios (10:0 ~ 5:5) were prepared using a pH-driven approach. In comparison with gliadin nanoparticles, complex nanoparticles have shown enhanced stability against neutral pH, ions, and boiling. They remained stable under neutral conditions at NaCl concentrations ranging from 0 to 100 mmol L-1 and even when boiled at 100 °C for 90 min. These nanoparticles were capable of effectively reducing oil-water interfacial tension (5 ~ 11 mNm-1 ) but a higher amount of shellac in the nanoparticles compromised their ability to lower interfacial tension. Moreover, the wettability of the nanoparticles changed as the gliadin/shellac mass ratio changed, leading to a range of three-phase contact angles from 52.41° to 84.85°. Notably, complex nanoparticles with a gliadin/shellac mass ratio of 8:2 (G/S 8:2) showed a contact angle of 84.85°, which is considered suitable for the Pickering stabilization mechanism. Moreover, these nanoparticles exhibited the highest emulsifying activity of 52.42 m2 g-1 and emulsifying stability of 65.33%. The findings of the study revealed that gliadin/shellac complex nanoparticles exhibited excellent resistance to environmental stress and demonstrated superior oil-water interfacial behavior. They have strong potential for further development as food emulsifiers or as nano-delivery systems for nutraceuticals. © 2023 Society of Chemical Industry.

Effect of hydrolyzed polyacrylamide on oil droplet stability in polymer-flooding produced water: variation of oil droplets diameter and oil–water interfacial properties

Hydrolyzed polyacrylamide (HPAM) in polymer flooding leads to stable oil-in-water emulsions, making the oil removal from polymer-flooding produced water (PFPW) more difficult. To elucidate HPAM’s effects on the oil separation performance of conventional physical separation process for PFPW, the stability, and diameter of oil droplets of simulated PFPW were accurately determined using the Turbiscan LAB expert. The results demonstrated that an increase in HPAM’s molecular weight and concentration led to a significant decrease in the diameter of oil droplets in simulated PFPW. When the molecular weight of HPAM increased from 6 to 18 MDa, there was a decrease in the Turbidity Scanning Index (TSI) values from 22.5 to 8.7, along with a significant decline in the diameter of oil droplets from 72.7 to 32.6 µm after a settling period of 40 min. Furthermore, a rise in HPAM concentration inhibited the enlargement of oil droplets. As HPAM concentration increased from 0 to 500 mg/L, the diameter of the oil droplets reduced by 42.1 µm after a 40 min settling period. HPAM's effect on restricting the growth of oil droplets remained relatively constant across oil concentrations ranging from 500 to 2500 mg/L. Moreover, increasing the molecular weight of HPAM from 6 to 18 MDa led to a 41.6% increase in PFPW's viscosity and a 38.9% decrease in oil-water interfacial tension, thereby inhibiting oil droplet coalescence. Our findings provide valuable fundamental guidance for the design of innovative separation methods for PFPW treatment.

Effect of konjac glucomannan with different degrees of deacetylation on the gel behavior of transglutaminase induced soybean protein isolate emulsion gels

In this study, the effect of konjac glucomannan (KGM) with different degrees of deacetylation (DD) on the gel properties of transglutaminase induced soybean protein isolate (SPI) emulsion gel was investigated. It was found that the three kinds of KGM increased the breaking force and water holding capacity, enhanced the freeze-thaw stability of the SPI emulsion gel, while KGM with DD of 59% (DKGM1) improved these properties to the largest extent. This was because SPI-DKGM1 had the lowest oil water interfacial tension, resulting in the formation of the most uniform and the smallest oil droplets, which then led to the formation of much denser gel network. Moreover, the hydrophobic interaction and hydrogen bonding between DKGM1 and SPI were the strongest compared with that of other KGM. Besides, FTIR results showed that SPI-DKGM1 emulsion gel had higher β-sheet content, which was conductive to the formation of a stable three-dimensional network structure. However, the combination of SPI and KGM with high DD (DKGM2, DD = 92%) destroyed the gel structure to some extent and resulted in emulsion gel with weakened gel properties compared with that of DKGM1. Therefore, KGM with proper DD was conducive to the formation of more ordered and much denser gel network structure, which then resulted in SPI emulsion gel with the best gel properties.

Preparation of amphiphilic Janus nanosheets based on thermally expandable microspheres and evaluation of their physical and chemical properties

Janus nanosheets can reduce the interfacial tension of oil and water and are of great significance for improving the recovery efficiency of remaining oil. A novel strategy for preparing amphiphilic Janus nanosheets is presented in this paper. Trialkoxysilane is adsorbed on the surface of thermally expandable microspheres (TEMS), and Janus spheres (TEMS@SiO2) are obtained by sol-gel treatment. Dodecyltrimethoxysilane (DTES) is used to modify TEMS@SiO2, which is combined with the thermal expansion of TEMS and the breaking of the outer shell of Janus spheres to prepare amino/alkyl composite silicon-based amphiphilic Janus nanosheets (ASAJN). Characterization of ASAJN is carried out via FTIR, TG, SEM, TEM, and contact angle tester, with the results showing that ASAJN boasts amphiphilicity and two-sidedness, and a sheet structure with a thickness of 210 nm. The stability, wettability evaluation, emulsification properties, and interface properties of ASAJN nanofluids have been evaluated, with the results showing that ASAJN nanofluids boast good stability without delamination after 30 days. ASAJN nanofluid can convert oil-wet core slices into water-wettable ones. ASAJN nanofluid manifests excellent emulsification, with the 240-hour emulsification index of ASAJN nanofluid and silica fluid respectively at0.40 and 0.021 under ultra-low concentration (1000 mg/L). ASAJN is obviously able to reduce oil–water interfacial tension. At 1000 mg/L (60 ℃) concentration, the oil-water interfacial tension is reduced to 2.6 mN/m, while that of nano-silica at the same concentration is 15.1 mN/m. ASAJN flooding can significantly improve the recovery efficiency of low-permeability reservoirs, increasing the recovery efficiency by 32.8 % at a permeability of 7.5 × 10-3 μm2.

Research on imbibition effect of surfactant fracturing fluid in offshore reservoirs with low permeability and high temperature

Surfactant imbibition can effectively improve the development effect of fracturing technique. In order to enhance oil recovery, a temperature resistant surfactant was selected using interfacial tension and contact angle testers based on the offshore reservoir conditions of high temperature and low permeability. Experiments on spontaneous and forced imbibition with artificial columnar cores were performed to optimize parameters of imbibition processes during fracturing in high temperature and low permeability reservoirs. Results show that among the three surfactants, amphoteric Gemini surfactant had a stable molecular structure with non-compressible hydrophobic groups which significantly reduced oil-water interfacial tension, enhanced rock wettability, and demonstrated good resistance to high temperatures The maximum recovery increase during amphoteric Gemini surfactant imbibition is 16.22%. The higher the core permeability, the higher the core inside pressure, and the longer the well shut-in time, the greater the forced imbibition effect. A proper well shut-in time and injection volume should be considered when using surfactant solution as fracturing liquid.

Enhancing oil recovery by alkane-modified molybdenum disulfide nanosheets with the optimum alkyl chain length: The balance between dispersity and hydrophobicity to achieve high interfacial activity

Alkane-modified molybdenum disulfide (AM-MoS2) nanosheets have attracted widespread interest as oil displacement agents for enhancing oil recovery due to their unique oil-water interfacial properties. However, the relationship between the interfacial activity and alkyl chain structure of AM-MoS2 is not comprehensively understood. In this study, 3AM-MoS2 nanosheets were prepared with MoS2 and alkylamines to study the effect of alkyl chain length on the oil-water interfacial activity of AM-MoS2 nanosheets under different salinity conditions. The AM-MoS2 nanosheets prepared with octylamine, dodecylamine, and octadecylamine were referred to as AM8-MoS2, AM12-MoS2, and AM18-MoS2, respectively. AM18-MoS2, which possesses the longest alkyl chain among all the samples, exhibited the highest oil-water interface adsorption ratio within the experimental concentration and salinity ranges. However, the changes in oil-water interfacial tension (IFT) did not agree with the changes in the interface adsorption ratio of nanosheets. AM18-MoS2 exhibited the best interfacial activity, and the IFT was lower than that of MoS2, AM8-MoS2 and AM12-MoS2 when the salinity was no more than 5000 mg/L, while AM12-MoS2 and AM8-MoS2 exhibited the best interfacial activity and the lowest IFT when the salinity reached 10,000 mg/L and 20,000 mg/L, respectively. Considering that the interface adsorption ratio of AM18-MoS2 was higher than that of the other samples under all the experimental conditions, the change in IFT and interfacial activity could be attributed to the change in the morphology of the adsorption layer of nanosheets. The decreased charge repulsion and the increased hydrodynamic size of nanosheets, which resulted from increased salinity, had positive and negative effects, respectively, on the morphology of the adsorption layer. The competition between the two effects resulted in the inflection point in the relationship between the IFT and salinity of AM-MoS2. The AM-MoS2 nanosheets with the optimum alkyl chain length balanced the dispersity and hydrophobicity, which contributed to achieving the best interfacial activity at a certain salinity.

Experimental study on countercurrent imbibition in tight oil reservoirs using nuclear magnetic resonance and AFM: Influence of liquid–liquid/solid interface characteristics

Countercurrent imbibition of the fracturing fluid is of much significance for enhancing oil production in tight oil reservoirs during the shut-in period after hydraulic fracturing. The addition of enhanced imbibition agents such as surfactants and nanoparticles into the polymer-based fracturing fluid is conducive to oil production. How different types of imbibition agents affect oil recovery and the applicable conditions for different imbibition agents, however, still need to be clarified. In this article, we used low-field nuclear magnetic resonance (NMR) to measure the one-dimensional (1D) oil signal profiles along the imbibition direction during the countercurrent imbibition process and determine the imbibition distance and water saturation of different imbibition agents including polymer, surfactant, nano-silica (NS) and NS-surfactant complexes. Moreover, by measuring oil–water interfacial tension (IFT), and the adhesion forces between alkanes and the hydrophobic surfaces before/after the imbibition agent treatments by atomic force microscope (AFM), the IFT reduction and wettability alteration abilities of these agents were evaluated. After the NS-surfactant complexes treatment, the adhesion force which represents the force required to pull off oil from the rock surface became the lowest (15.81 pN), merely a quarter of that of NS (73.48 pN) and surfactant (70.01 pN), indicating a superior capability of NS-surfactant to improve wettability. The imbibition efficiency of the four systems in terms of imbibition distance and oil recovery was: NS-surfactant complexes: 38.43 mm 13.2 % > nonionic surfactant: 32.15 mm 9.0 % > NS: 25.88 mm 7.6 % > polymer: 17.64 mm 4.9 %. NS-surfactant nanofluid displayed the longest imbibition distance and highest water saturation, thus possessing the highest imbibition oil recovery. Nonionic surfactant with an IFT of 4.19 mN/m could greatly reduce the IFT compared with NS (35.98 mN/m), but the recovery enhancement induced by IFT reduction was not significant. In contrast, the increase in oil recovery by wettability alteration was distinctly higher than that by IFT reduction, as indicated by the recovery difference between NS-surfactant complexes and surfactant. Accordingly, wettability alteration is the primary mechanism to enhance imbibition oil recovery when ultralow IFT cannot be achieved. This research provides guidance on which type of imbibition agent should be selected to improve imbibition efficiency.

Design of Novel Knot-like Structures Based on Ovotransferrin Fibril-Gum Arabic Complexes: Effective Strategies to Stabilize Pickering Emulsions.

This work aimed to clarify the effects of gum arabic (GA) on the morphology and properties of ovotransferrin fibrils (OVTFs). By constructing OVTF-GA complexes and exploring the dispersion stability, turbidity and the ζ-potential of the complexes, the optimum mass ratio of OVTFs to GA and pH for complex formation were confirmed as being 1:1 and pH 4.6, respectively. The interaction between OVTFs and GA was determined to be predominantly driven by electrostatic attraction. The OVTF-GA complexes exhibited a knot-like structure when observed using atomic force microscopy. Then, OVTFs and OVTF-GA complexes were compared in terms of contact angle, surface hydrophobicity and dynamic interfacial tension. The combination of OVTFs and GA decreased the contact angle of OVTFs from 80.85° to 70.36°. In comparison with OVTFs, OVTF-GA complexes reduced the oil-water interfacial tension to a lower level (8.14 mN/m). Furthermore, the capacities of OVTF-GA complexes in stabilizing emulsions were explored. OVTF-GA complex-stabilized oleogel-based Pickering emulsion (OGPE) was constructed, and OVTF-stabilized oleogel-based Pickering emulsion (OPE) was used as the control. OGPE had a higher emulsified phase volume fraction (EPVF) and stability index (SI). The EPVF of OGPE was 100.0% and 99.4% before and after one-month storage, respectively, compared with 98.3% and 95.7% of OPE. This work can provide some useful references for the design of biopolymers with novel structures composed of protein fibrils and polysaccharides, which may also help to construct and apply protein fibril-polysaccharide complexes under specific needs.

Insight into functional groups of salt compounds on the performance of viscoelastic surfactant-based fluids

Clean fracturing fluids (CFFs) hold great potential for the development of unconventional reservoirs due to their characteristics (e.g., fracturing-oil expulsion integration and low formation damage). Organic salts, as adjuvants, play a significant role in regulating the performance of CFFs. In this work, four CFFs containing different organic salts were prepared to investigate the impact of functional groups in organic salts on the CFF performance. Results show that the functional groups markedly influence the rheological properties, temperature resistance and drag reduction performances of CFFs through inducing the micelle formation and thus enhancing the micelle network strength. Sodium 4-vinylbenzenesulfonate (SV) with vinyl endowed the CFF with the stronger micelle network. Furthermore, the functional groups were found to impact the adsorption of surfactants at interface, which affects the oil–water interfacial tensions and regulates the spontaneous imbibition performance of CFFs. SV enables a higher imbibition efficiency of 25.6 % after 90 h. Density functional theory (DFT) calculation results confirmed that the functional groups of salts are capable of manipulating the interactions between salt anions and surfactant, ultimately determining the CFF performance. This work provides guidance for the selection of salt additives to improve the CFF performance.

Pore-scale investigation on the flow behavior and oil displacement of ultralow IFT surfactant flooding based on CFD simulation

In order to investigate the flow behavior and oil displacement of ultralow interfacial tension (IFT) surfactant flooding, the experimentally validated computational fluid dynamics simulation model is constructed by coupling the Navier-Stokes equations and the Cahn-Hilliard equation. The mixed surfactant solution is prepared using the ionic liquid surfactant and the nonionic surfactant, and the fluid parameters are measured experimentally. Due to the reduced oil-water IFT, the low pressure drop in porous medium and the decreased oil viscosity, ultralow IFT surfactant contributes to increasing the mobility ability of the fluid front in pores, and its optimal injection velocity is 0.01 m/s. In addition, the sweep area of surfactant flooding in oil-wet porous medium is significantly larger than that of brine flooding because of wettability alteration. Finally, for different porosity models, the residual oil content and the pressure drop of surfactant flooding show a 66.7% and 71.4% decrease than those of brine flooding, respectively, proving its better displacement performance.

Analysis of the Influencing Factors on the Extraction of Residual Oil through the Gel Foam Flooding of Underground Reservoirs in the Tahe Oilfield.

Fractured-vuggy reservoirs are mainly composed of three types: underground rivers, vugs, and fractured-vuggy structures. Based on the similarity criterion, a 3D model can truly reflect the characteristics of the multi-scale space of a fractured-vuggy reservoir, and it can reflect fluid flow laws in the formation. Water flooding, gas flooding, and gel foam flooding were carried out in the model sequentially. Based on gas flooding, the enhanced recovery ratio of gel foam flooding in the underground river was approximately 12%. By changing the injection rate, the average recovery ratio of nitrogen flooding was 6.84% higher than that of other injection rates at 5 mL/min, and that of gel foam flooding was 1.88% higher than that of other injection rates at 5 mL/min. The experimental results showed that the gel foam induced four oil displacement mechanisms, which selectively plugged high-permeability channels, controlled the mobility ratio, reduced oil-water interfacial tension, and changed the wettability of rock surfaces. With different injection-production methods, gel foam flooding can spread across two underground river channels. Two cases of nitrogen flooding affected one underground river channel and two underground river channels. By adjusting the injection rate, it was found that after nitrogen flooding, there were mainly four types of residual oil, and gel foam flooding mainly yielded three types of remaining oil. This study verified the influencing factors of extracting residual oil from an underground river and provides theoretical support for the subsequent application of gel foam flooding in underground rivers.

Impact of mixing energy and dispersant dosage on oil dispersion and sedimentation with microplastics in the marine environment

Recently, the fate of spilled oil in the presence of microplastics (MPs) in the sea has attracted attention of researchers. Merey crude oil and polyethylene terephthalate (PET) were used as the experimental materials in this study. The effects of mixing energy and dispersant dosage on oil dispersion and sedimentation in the presence of MPs in the water column were investigated by laboratory experiments simulating actual sea conditions. The increase of mixing energy showed a promoting effect on oil dispersion. When the oscillation frequency increased from 140 rpm to 180 rpm, the oil dispersion efficiency (ODE) ranged from 2.1 %–3.7 % to 17.4 %–30.8 %, and the volumetric mean diameter (VMD) of the suspended oil droplets/MPs-oil agglomerates (MOA) decreased from 99.9–131.4 μm to 76.6–88.2 μm after 2 h oscillation. The application of chemical dispersant led to an increase in both the quantity and size of the formed sunken MPs-oil-dispersant agglomerates (MODA). At the dispersant-to-oil ratio (DOR) of 1:5, the ODE declined from 77.7 % to 62.6 % when the MPs concentration increased from 0 to 150 mg/L, while the oil sinking efficiency (OSE) rose from 3.4 % to 15.6 % when the MPs increased from 25 to 150 mg/L; the maximum size of the sunken MODA reached 13.0 mm, and the total volume of the MODA formed per unit volume oil reached 389.7 μL/mL oil at the MPs concentration of 150 mg/L. Meanwhile, the results showed that the presence of MPs inhibited the oil dispersion by increasing the oil-water interfacial tension. The outcomes of this work may provide assistance in predicting the transport of spilled oil and developing emergency measures.

Pore-scale study of dynamic surfactant adsorption under immiscible displacement in porous media: effect of wetting conditions

Surfactant flooding is one of the most effective methods of enhanced oil recovery, because it helps to reduce oil-water interfacial tension and mobilize the residual oil. Surfactant molecules can be adsorbed on the particle surface. This paper presents a systematic study of the dynamic adsorption of a water-soluble surfactant during flooding of oil-saturated porous media. The novelty lies in the study of dynamic adsorption with multiphase flows in porous media, which provides new trends. The main goal is to reveal the effect of wetting angle, interfacial tension, flow rate, and adsorption rate constant on the adsorbed amount in the immiscible displacement. Lattice Boltzmann simulations are used to study this problem. The flow regions are represented by digital images of granular porous structures. A map characterizing the adsorbed amount of surfactant versus wetting angle and interfacial tension has been presented. The results showed that increasing the wetting angle positively affects the adsorbed amount, while increasing interfacial tension suppresses the adsorbed value. Different patterns of dynamic adsorption in dependence on flow rate and adsorption rate constant have been identified. At low adsorption rates, regardless of the wetting angle and interfacial tension, a decrease in the flow rate contributes to an increase in the adsorbed amount. At high adsorption rates, the adsorbed amount is determined by the displacement efficiency. The obtained tendencies have been validated by performing a series of simulations on a group of porous structures. It has been found that the prediction reliability of the adsorbed amount increases with increasing wetting angle and capillary number.

Nonequilibrium Colloids: Temperature-Induced Bouquet Formation of Flower-like Micelles as a Time-Domain-Shifting Macromolecular Heat Alert.

Climate change requires enhanced autonomous temperature monitoring during logistics/transport. A cheap approach comprises the use of temperature-sensitive copolymers that undergo temperature-induced irreversible coagulation. The synthesis/characterization of pentablock copolymers (PBCP) starting from poloxamer PEO130-b-PPO44-b-PEO130 (poly(ethylene oxide)130-b-poly(propylene oxide)44-b-poly(ethylene oxide)130) and adding two terminal qPDMAEMA85 (quaternized poly[(2-dimethylamino)ethyl methacrylate]85) blocks is presented. Mixing of PBCP solutions with hexacyanoferrate(III)/ferricyanide solutions leads to a reduction of the decane/water interfacial tension accompanied by a co/self-assembly toward flower-like micelles in cold water because of the formation of an insoluble/hydrophobic qPDMAEMA/ferricyanide complex. In cold water, the PEO/PPO blocks provide colloidal stability over months. In hot water, the temperature-responsive PPO block is dehydrated, leading to a pronounced temperature dependence of the oil-water interfacial tension. In solution, the sticky PPO segments exposed at the micellar corona cause a colloidal clustering above a certain threshold temperature, which follows Smoluchowski-type kinetics. This coagulation remains for months even after cooling, indicating the presence of a kinetically trapped nonequilibrium state for at least one of the observed micellar structures. Therefore, the system memorizes a previous suffering of heat. This phenomenon is linked to an exchange of qPDMAEMA-blocks bridging the micellar cores after PPO-induced clustering. The addition of ferrous ions hampers the exchange, leading to the reversible coagulation of Prussian blue loaded micelles. Hence, the Fe2+ addition causes a shift from history monitoring to the sensing of the present temperature. Presumably, the system can be adapted for different temperatures in order to monitor transport and storage in a simple way. Hence, these polymeric "flowers" could contribute to preventing waste and sustaining the quality of goods (e.g., food) by temperature-induced bouquet formation, where an irreversible exchange of "tentacles" between the flowers stabilizes the bouquet at other temperatures as well.

Interfacial properties, decompression, and augmented injection of amphiphilic carbon dots and surfactant mixtures

The mixing properties of amphiphilic carbon dots named C12-SCDs with a cationic surfactant (Dodecyl trimethyl ammonium bromide, DTAB) and an anionic surfactant (Sodium dodecyl sulfate, SDS) were investigated. Results indicated that surfactants DTAB and SDS show a synergistic effect in reducing surface tension with C12-SCDs. The synergistic effect of the DTAB/C12-SCDs mixture is more prominent than the SDS/C12-SCDs mixture, which may result from the electrostatic attraction between DTAB and C12-SCDs. Meanwhile, adding inorganic salts, the surface tension of these mixtures shows a trend of first decreasing slightly and then increasing. The DTAB/C12-SCDs mixture resists strong acids but not alkali environments. However, the surface tension of the SDS/C12-SCDs mixture gradually increases with the increase in pH. In addition, these mixtures have temperature-resistance properties. C12-SCDs and surfactants (DTAB and SDS) also have a synergistic effect in reducing the crude oil-water interfacial tension. Meanwhile, the DTAB/C12-SCDs and SDS/C12-SCDs mixtures have excellent wettability alternation performance. C12-SCDs and surfactants can form a mixed adsorption layer to promote the wettability alternation performance. The depressurization rates of DTAB, SDS, C12-SCDs, DTAB/ C12-SCDs mixture, and SDS/C12-SCDs mixture are 10.42 %, 11.54 %, 22.91 %, 26.32 %, and 24.75 %, respectively. The DTAB/C12-CDs and SDS/C12-CDs mixtures can effectively remove the oil film on the core surface, thus improving the channel of injected water. At the same time, these mixtures can be adsorbed on the surface of the hydrophilic core to form a hydrophobic surface, and the injection of water produces a hydrophobic slip effect. Finally, reducing the surface tension of water can also effectively reduce the injection pressure.

Dissipative Particle Dynamics-Based Simulation of the Effect of Asphaltene Structure on Oil-Water Interface Properties.

Asphaltenes are the main substances that stabilize emulsions during the production, processing, and transport of crude oil. The purpose of this research is to investigate the process of asphaltenes forming interfacial films at the oil-water interface by means of dissipative particle dynamics (DPD) and the effect of asphaltenes of different structures on the oil-water interface during the formation of interfacial film. It is demonstrated that the thickness of the interfacial film formed at the oil-water interface gradually increases as the asphaltene concentration rises and the amount of asphaltene adsorbed at the oil-water interface gradually multiplies. Both the number and type of heteroatoms in asphaltenes affect the interfacial behavior of asphaltenes. The interface activity of asphaltenes can be enhanced by increasing the number of heteroatoms in the asphaltene, and the type of heteroatom affects as well the interfacial activity of the asphaltene as it affects the aggregation behavior of the asphaltene in the system. As the number of asphaltene aromatic rings increases, the oil-water interfacial tension (IFT) trends down gradually, while the effect of alkyl side chains on the reduction of IFT of asphaltenes is different, and asphaltenes with medium length alkyl side chains can reduce IFT more efficiently.