Surfactant Adsorption Research Articles

Geochemical Analysis of Hardness on the Adsorption of Surfactants in Carbonates Under Severe Thermodynamic Conditions: Surface Complexation Modeling Approach

Abstract Several core-flooding-based experimental studies demonstrated the effect of calcium and magnesium ions and it is found that these hard ions have detrimental effects on oil recovery during chemical-enhanced oil recovery operations. However, studies regarding the coupled effect of hard ions and surfactant adsorption are very limited. Thus, this study aims to present a novel approach that can capture mineral-brine, brine-oil, and brine-surfactant interactions in the presence of hard ions (Ca2+ and Mg2+). Also, we introduced four oil-surfactant-based surface complexation geochemical reactions (SCGR) in the presence of hard ions for the first time to analyze the oil-surfactant interactions. The developed thermodynamic-based geochemical model is compared and validated with recent core-flooding data. Our results illustrate that the use of oil-surfactant SCGR is important and should be captured for detailed surfactant adsorption. Thus, we observed that in the presence of hard ions, surfactant adsorption increases with the increase in temperature, which is due to the surge in kinetic energy. We also observed that a reduction in hardness reduces the adsorption of surfactants. Additionally, increasing surfactant concentration led to a minor increase in the adsorption of surfactant with a significant increase in its concentration in the discharge/effluent. Therefore, the hard ions (Ca2+ and Mg2+) concentration has a substantial negative effect, as they reduce the solubility of surfactant and increase its adsorption. Furthermore, the lowest level of surfactant adsorption was accomplished by injecting ten times diluted water (<0.070 mg/g).

Interactions between fluorocarbon surfactant and coal dust at macro, meso and molecular scales and their applications in coal dust control

Surfactants play an important role in the field of coal dust prevention, among which fluorocarbon surfactants have the advantages of low surface tension and have the potential to become mine dust suppressants. In this study, the wettability of fluorocarbon surfactant (OBS) on coal dust was studied from macro experiments, meso dust mist coupling and micro molecular simulation. The results showed that the surface tension of 0.06% OBS was as low as 17.6 mN/m, and the median particle size of coal dust reached 60.25 μm after wetting coal dust. Coal dust particles are easier to bond with each other into large particles, thus promoting settlement; During the meso collision between droplets and coal dust particles, OBS droplets showed excellent wetting and spreading effect, and the droplet state was stable, and the optimal spraying velocity was determined to be 20–30 m/s; At the molecular level, the diffusion coefficient of water molecules in the OBS system is minimally 0.46 Å2/ps, indicating a strong ability to constrain water molecules. The strength and energy of the hydrogen bonds formed with water molecules were greater than those of hydrocarbon surfactants, resulting in the best adsorption of water molecules. Additionally, it was found that the law of attractive and competitive adsorption of different surfactants in wetting coal dust is based on the difference in positive and negative electrostatic potential, where the greater the difference, the stronger the interaction. This provides a theoretical reference for judging the wetting performance of different surfactants at the molecular level.

Screening of Chemicals to Enhance Oil Recovery in a Mature Sandstone Oilfield in Kazakhstan: Overcoming Challenges of High Residual Oil

Chemical flooding, such as alkaline-surfactant (AS) or nanoparticles-surfactant (NS) flooding, is an enhanced oil recovery (EOR) technique that has been increasingly utilized to enhance the oil production rate and recovery factor while reducing chemical adsorption. The AS/NS flooding process involves the injection of a mixture of surfactant and alkali/nanoparticles solutions into an oil reservoir to reduce the interfacial tension between the oil and water phases by surfactant and lower surfactant adsorption by alkali or nanoparticles (NPs) to improve the residual oil recovery. In this study, the AS/NS flooding is evaluated for a Kazakhstani oilfield by systematically screening the chemical constituents involved. Field A in Kazakhstan, one of the oldest fields in the country, has been waterflooded for decades and has not produced even 50% of the original oil in place (OOIP). Currently, the water cut of the field is more than 90%, with a high residual oil saturation. Therefore, besides polymer flooding to control mobility, chemical EOR is proposed as a tertiary recovery method to mobilize residual oil. This study aimed to screen chemicals, including surfactant, alkali, and NPs, to design an effective AS/NS flooding program for the target field. The study focused on conducting laboratory experiments to identify the most effective surfactant and further optimize its performance by screening suitable alkaline and NPs based on their compatibility, stability, and adsorption behavior under reservoir conditions. The performance of the screened chemicals in the porous media was analyzed by a set of coreflood experiments. The findings of the study indicated that alkali agents, particularly sodium carbonate, positively affected surfactant performance by reducing its adsorption by 9–21%. The most effective surfactant combination was found, which gave Winsor type III microemulsion and the lowest interfacial tension (IFT) of 0.2 mN/m. The coreflood tests were conducted with the screened surfactant, alkali, and NPs. Both AS and NS tests demonstrated high residual oil recovery and microemulsion production. However, NS flooding performed better as the incremental oil recovery by NS flooding was 5% higher than standalone surfactant flooding and 9% higher than AS flooding. The results of this screening study helped in designing an efficient chemical formulation to improve the remaining oil recovery from Field A. The findings of this study can be used to design EOR projects for oil fields similar to Field A.

Water separation from diesel fuel using high surface area 3D-printed aerogel constructs

This work reports removal of emulsified water droplets from ultralow sulfur diesel (ULSD) fuel using high surface area aerogel filter media constructs. A synergistic combination of additive manufacturing and sol–gel chemistry is used for fabrication of the filter media constructs from high surface area (>200 m2/g) and high porosity (>90%) polyimide and syndiotactic polystyrene aerogels that are grown using sol–gel processes inside the load-bearing 3D-printed polymeric constructs of polyamide and high impact polystyrene respectively. This paper evaluates the roles of several factors on water separation efficiency, such as surface energy of polymer media on wetting, surfactant adsorption by the high surface area polymer media, and size exclusion of water droplets by smaller aerogel pores. The surfactant-stabilized water droplets in ULSD can be removed with a separation efficiency of up to 95% using these mechanically strong aerogel constructs.

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.

ATR FTIR spectroscopy of protein and surfactant adsorption to the oil-water interface

An oil-infused polyelectrolyte multilayer (PEM) immersed in aqueous solution is a valid mimic for an oil-water interface, that can be used to probe adsorption of surfactants (including co-/competitive adsorption) using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR). A PEM has been formed on an ATR internal reflection element, dried and then re-solvated with oil, then exposed to a flowing solution of protein, and subsequently a solution of surfactant. The PEM had undergone prior characterization with atomic force microscopy (AFM). The experiment was replicated using profile analysis tensiometry (PAT). The PEM displays a high degree of solvation with oil; it retains most of this oil in the presence of flowing aqueous solution. FTIR spectra confirmed adsorption of a dairy protein (β-lactoglobulin) to the medium chain triglyceride (MCT)-water interface, and the response of the adsorbed protein layer to a common food formulation surfactant (Tween 60) in the aqueous phase above the interface. The protein is observed to adsorb strongly and irreversibly to the MCT oil-water interface, and the Tween 60 molecules are seen to co-adsorb rather than displace the protein. This observation is supported by measurements of sequential co-adsorption undertaken with PAT.

Electrical dehydration performance of shale oil: From emulsification characteristics to dehydration mechanisms

Shale oil, as a successor to ordinary crude oil, has received extensive attention. However, the high-stability shale oil emulsions are still challenging for electrical dehydration systems. In this work, the differences between shale oil and ordinary crude oil were compared in terms of emulsion droplet size, physical properties and components to clarify the emulsification characteristics of shale oil and reveal its electrical dehydration mechanism. To this end, comprehensive electrical dehydration experiments were carried out under different parameters and transformers. The results showed droplet diameters of shale oil emulsions less than 10 µm, a value much smaller than that of crude oil. Shale oils with high viscous contained lots of natural emulsifiers, promoting the formation of the rigid asphalt film and wax crystal network structure. The synergistic adsorption of surfactant and paraffin molecules and the film formation of asphaltenes promoted by resins make shale oil display lower interfacial tension and higher interfacial film pressure. The above characteristics were the main reasons behind the formation of shale oil stable emulsions. Factors, such as electric field frequency, dehydration temperature, dehydration time, and demulsifier concentration influenced the emulsification characteristics and dehydration performance of shale oils at variable degrees. The dehydration performances of high-frequency transformer (Transformer B) and ultra-high-frequency transformer (Transformer C) on shale oil emulsion SH-1 were better than that of low-frequency transformer (Transformer A) due to tensile breakup or oscillatory coalescence of droplets under different electric field conditions. Considering energy consumption and economy comprehensively, Transformer C has excellent application potential. The analyses also show that high-frequency, heating and adding demulsifier are the key and necessary factors in the electric dewatering treatment of shale oil. In sum, these results look useful for future design optimization of shale electrical dehydration devices.

Adsorption of surfactant molecules onto the surface of colloidal particles: Case of like-charged species

Mixed systems of nanoparticles and surfactants have a broad range of applications from consumer products and medicine to inkjet printing and oil recovery. The interparticle interactions can be tuned in presence of surfactants and are dependent on surface charge of both species, particle’s wettability, surfactant solubility, and solution conditions such as electrolyte concentration and pH. The case of oppositely charged particles and surfactants has been extensively examined in the literature, primarily to tune the wettability of particles. In contrast, the behavior in systems of like-charged species such as negatively charged particles and anionic surfactants remains poorly understood, with conflicting findings reported in previous studies on the adsorption of surfactants. By conducting a comprehensive investigation, in this study we shed light on the factors that influence the adsorption of surfactant onto the particle surface, both promoting and preventing it, and unravel the underlying mechanisms governing such behavior. Silica nanoparticles were used as the negatively charged particle, sodium dodecyl sulfate (SDS) was used as the surfactant and potassium nitrate was used as the salt, while the pH was adjusted by potassium hydroxide and nitric acid, to investigate the effect of surfactants on the surface characteristics of the silica nanoparticles under various operating conditions. The zeta potential of particles along with the solution conductivity were obtained via mobility measurements. Using this information, the solution’s Debye length and the particle’s surface charge density were estimated. It was found that interpreting the outcome solely based on the zeta potential data might not reveal the adsorption of SDS onto the particle surface as no supercharging effect could be detected in some cases. However, shifting the perspective to charge density shows that SDS increased the particles charge density for pH values in the range of 2–5, corresponding to the pH conditions at which vicinal and geminal silanol groups are dissociated. This effect was more pronounced at moderate total ionic strengths between 1 and 10 mM, where SDS activity was found to be higher and the Debye length was sufficiently short. The increase in the particle’s charge density was attributed to the tail-down adsorption of SDS onto the particle surface via entropically-driven interactions. These findings offer valuable insights into like-charged mixed particle/surfactant systems and bring clarity to the scientific community regarding this complex and previously inconclusive topic.

Static and dynamic adsorption of a gemini surfactant on a carbonate rock in the presence of low salinity water

In chemical enhanced oil recovery (cEOR) techniques, surfactants are extensively used for enhancing oil recovery by reducing interfacial tension and/or modifying wettability. However, the effectiveness and economic feasibility of the cEOR process are compromised due to the adsorption of surfactants on rock surfaces. Therefore, surfactant adsorption must be reduced to make the cEOR process efficient and economical. Herein, the synergic application of low salinity water and a cationic gemini surfactant was investigated in a carbonate rock. Firstly, the interfacial tension (IFT) of the oil-brine interface with surfactant at various temperatures was measured. Subsequently, the rock wettability was determined under high-pressure and high-temperature conditions. Finally, the study examined the impact of low salinity water on the adsorption of the cationic gemini surfactant, both statically and dynamically. The results showed that the low salinity water condition does not cause a significant impact on the IFT reduction and wettability alteration as compared to the high salinity water conditions. However, the low salinity water condition reduced the surfactant’s static adsorption on the carbonate core by four folds as compared to seawater. The core flood results showed a significantly lower amount of dynamic adsorption (0.11 mg/g-rock) using low salinity water conditions. Employing such a method aids industrialists and researchers in developing a cost-effective and efficient cEOR process.

Magnetic and luminescent properties of bifunctional composite Fe3O4@Y2O2S:Eu3+

As a kind of non-destructive testing method, magnetic particle inspection is widely used in the fields of aviation and high-speed rail. The properties of magnetic fluorescent bifunctional composites, such as fluorescence intensity and magnetic properties, have increasing demands in magnetic particle inspection. Rare earth compounds offer potential as novel materials for fluorescent magnetic bifunctional composites due to their excellent optical properties and extremely narrow emission spectra. In this work, the rare earth fluorescent material Y2O2S:Eu3+ was synthesized by solid-state reaction method. Fe3O4 nanoparticles prepared by hydrothermal method were uniformly coated on the Y2O2S:Eu3+ particles through physical adsorption of surfactants. The obtained Fe3O4@Y2O2S:Eu3+ exhibits dark red color under the ultraviolet light. In addition, X-ray diffraction, morphology, photoluminescence and hysteresis loop of Fe3O4@Y2O2S:Eu3+ were investigated. The luminescence mechanism of Y2O2S:Eu3+ is described in detail. Fe3O4@Y2O2S:Eu3+ displays good paramagnetism and has a good controllability under a magnetic field. The magnetic particle inspection of Fe3O4@Y2O2S:Eu3+ was performed using a 4-pole electromagnet and a test piece shim. The magnetic fluorescent bifunctional composite presented in this work can be applied for non-destructive testing.

Enhanced Oil Recovery by Surfactant Injection was improved during the Last 50 Years Thanks to the Multivariable HLD Formulation Equation

This report reviews the progress in Enhanced Oil Recovery (EOR) through surfactant injection over the past half century from 1974, with a specific focus on the role of the multivariable Hydrophilic-Lipophilic Deviation (HLD) formulation equation in different expressions. This equation has been instrumental in optimizing surfactant formulations for EOR, enabling the fine-tuning of surfactant types and properties to match specific reservoir conditions like brine salinity, crude characteristic, temperature and even pressure. This short assesment discusses the evolution of surfactant types, and their impact on EOR efficiency for a given reservoir specifications. It highlights the role of intramolecular and intermolecular mixing in surfactant performance, and the benefits of using a multivariable HLD equation to predict and optimize the injected formulation. Furthermore, it explores the challenges and solutions related to surfactant adsorption, aggregation, precipitation, and effect on phase behavior and interfacial tension, and how these factors have to be considered when using surfactants for EOR projects. This review aims to address the existing gaps in the literature, such as the complex effects of surfactant mixtures with insensitivity to temperature and injected composition (amphiphilic concentration and water/oil ratio) that make difficult to propose a unified approach for different petroleum reservoirs. It concludes a discussion on the state of the art and future of surfactant EOR, emphasizing the need for continued research and collaboration across academic and industrial sectors

The Interfacial Dilational Rheology Properties of Betaine Solutions: Effect of Anionic Surfactant and Polymer.

Interfacial dilational rheology is one of the important means to explore the interfacial properties of adsorption films. In this paper, the interfacial rheological properties of the mixed system of sulfobetaine ASB with a linear alkyl group and two anionic surfactants, petroleum sulfonate (PS) and alkyl polyoxyethylene carboxylate (AEC), were investigated by interfacial dilational rheology. The effect of the introduction of polymer hydrophobically modified polyacrylamide (HMPAM) on the interfacial properties of the mixed system was analyzed. In this experiment, the surfactant solution was used as the external phase and n-decane was used as the internal phase. A periodic sinusoidal disturbance of 0.1 Hz was applied to the n-decane droplets, and the changes of parameters such as droplet interfacial tension and interfacial area were monitored in real time with the help of a computer. The results show that the betaine ASB molecule responds to the dilation and compression of the interface through the change of ion head orientation, while the feedback behavior of petroleum sulfonate PS and AEC molecules embedded with oxygen vinyl groups in the molecule is diffusion and exchange between the interface and the bulk phase. Therefore, the interface film formed by ASB alone is higher, and the film formed by PS and AEC molecules alone is relatively lower. After adding two kinds of anionic surfactants to the betaine system, the ionic head of PS or AEC molecules will be attached to the positive center of the hydrophilic group of ASB molecules by electrostatic attraction and no longer adsorb and desorb with the interface deformation. The interfacial rheological properties of the compound system are still dominated by betaine, with higher dilational modulus and lower phase angle. When a small amount of HMPAM is added, or the content of hydrophobic monomer AMPS in the bulk phase is low, the intermolecular interaction at the interface is enhanced, the slow relaxation process is intensified, and the interfacial film strength is increased. As the content of AMPS further increases, hydrophobic blocks and surfactant molecules will form interfacial aggregates similar to mixed micelles at the oil-water interface, which will regulate the properties of the film by affecting the adsorption of surfactants at the interface. As long as the interfacial tension is the same, the properties of the interfacial film are the same. Based on the colloid interface science and the background of enhanced oil recovery, this study provides a reference for the field application of chemical flooding formulations.

Effect of Polyethyleneimine Cationic Surfactant on Morphology and Corrosion Resistance of Electrodeposited Ni-Co-SiC Composite Coatings

Ni-Co-SiC composite coatings were prepared by modified watt-type plating solution with 40 nm SiC particles. The effects of polyethyleneimine (PEI) on the dispersion of SiC nanoparticles and the hardness and corrosion resistance of Ni-Co-SiC coatings were studied. The electrode reaction process was measured by cyclic voltammetry. The results showed that when the PEI concentration was 0.06 g/L, the peak current was the highest. SiC distribution in Ni-Co-SiC coatings was relatively uniform and the coating was flat and dense. With the increase in PEI concentration, the hardness and corrosion resistance showed a trend of increasing first and then decreasing. The hardness and corrosion resistance were at their best with 0.06 g/L PEI. Pretreatment effectively avoided the competitive adsorption of surfactant and other additives on the surface of SiC particles. PEI was preferentially adsorbed on the surface of SiC particles by pretreatment. Steric resistance was formed, which inhibited the agglomeration of nanoparticles and make SiC particles more evenly dispersed into the coating. The hardness was significantly increased by 119.26 Hv, and the corrosion resistance improved accordingly.

Adsorption of a photoresponsive surfactant at the water–quartz interface: The role of UV irradiation and cucurbit[7]uril

It is a challenge to develop a method of controlling the adsorption of small molecules at different interfaces. Here, we report the photocontrolled adsorption of a surfactant containing an azobenzene group (AZO) at the aqueous solution–quartz interface. The adsorption of the surfactant decreases at the interface and the corresponding adsorption layer becomes more rigid after UV irradiation. In addition, the adsorption of the surfactant at the interface is also decreased by addition of cucurbit[7]uril (Q[7]) due to the host–guest interaction between Q[7] and the surfactant. Adsorption of surfactant is stronger at the aqueous solution–quartz interface than at the aqueous solution–air one. The aqueous solution–quartz interfacial tension (γsl) of the surfactant is decreased by using UV irradiation or Q[7]. The adsorption mechanisms of the surfactant were investigated. Our study provides the methods to control the adsorption of the small molecules at the aqueous solution–solid interface.

The influence of divalent cations on the dynamic surface tension of sodium dodecylbenzenesulfonate solutions

The kinetics of surfactant adsorption at interfaces is crucial in many industrial settings. Maximum bubble pressure tensiometry allows accessing the adsorption at time scales of tens of ms to uncover the initial stages of surfactant diffusion to the interface. This method was used to investigate electrolyte solutions of sodium dodecylbenzenesulfonate (SDBS), specifically targeting how the presence of small amounts of divalent cations (Mg2+, Ca2+, Sr2+ and Ba2+) influenced the adsorption kinetics and equilibrium. The dynamic surface tensions revealed that the adsorption of SDBS was strongly influenced by the presence of divalent cations due to strong interactions with the anionic surfactant. In addition, the type (i.e. size) of cations played a role. The strong divalent cation-surfactant interactions lead to distinct lowering of surfactant diffusion coefficients, calculated using the short-time approximation solution of the Ward-Tordai equation. The diffusion coefficients were slightly and similarly lowered for all types of divalent cations when the surfactant concentration was increased up to the critical micelle concentration (CMC). Above CMC, the diffusion coefficients increased steadily depending on the divalent cation. It was speculated that this could be due to differences in structure and aggregation numbers of micelles and slower disassembly of micelles to supply monomers for adsorption. Furthermore, CMC of SDBS was reduced according to the Hofmeister series in the presence of divalent cations.

Chromatographic behavior of polar compounds in the transition between reversed-phase and submicellar/micellar liquid chromatography

Micellar liquid chromatography (MLC) is a reversed-phase liquid chromatography (RPLC) mode employing a surfactant, typically sodium dodecyl sulfate (SDS), which is biodegradable, in an aqueous or aqueous-organic mobile phase above its critical micellar concentration (CMC). Under these conditions, substantial alterations in retention, selectivity and peak profile occur in comparison to RPLC using conventional hydro-organic mobile phases. These changes arise from the presence of micelles in the mobile phase and the adsorption of surfactant on the stationary phase. In this work, the chromatographic performance of polar compounds of diverse nature is investigated using mobile phases containing SDS below and above its CMC in the presence of acetonitrile. Three nucleosides, four diuretics, and four sulfonamides, all of biomedical and pharmaceutical significance and possessing distinct acid-base characteristics, were chosen as probe compounds. Modifications in retention and peak shape were investigated using experimental conditions that enable the transition from submicellar to micellar conditions. A comparison was also made with conventional RPLC. Analysing the polar compounds with RPLC under low submicellar or micellar conditions significantly decreases the consumption of organic solvent in comparison to hydrophilic liquid chromatography (HILIC).

Adsorption of poly(oxyethylene) and hydroxyl group-containing nonionic surfactants on silica particles in NH4OH solution and its effect on the interaction force with Si surface

In the semiconductor manufacturing processes, surface cleaning is one of the most critical steps because particle contamination directly affects device yield. In addition, surface etching and oxidation should be minimized during the particle removal process. In this study, the dissolved oxygen concentration (DOC) in an NH4OH solution was reduced to suppress oxidation of Si. Additionally, nonionic surfactants were added to the solution to suppress the Si surface roughening and improve the particle removal efficiency in the NH4OH solution. Nonionic surfactant molecules were adsorbed on the Si surface, preventing the Si surface from attack by OH-. In addition, they were also adsorbed on the silica particle surfaces, producing repulsive hydration and osmotic forces between the adsorbed surfaces of the Si and silica particles while reducing the adhesion force between them. As a result, more than 95 % of particle removal efficiency and less than 0.6 nm of surface roughness were obtained when the particle-contaminated Si surface was treated with a low-DOC NH4OH solution containing a nonionic surfactant.

Results of modelling the effect of temperature on the thickness of the surfactants layer

Problem. Earthmoving machines operate under high loads, so their tribo-joints periodically operate under unsteady load conditions, which leads to their increased wear and, as a result, a rapid decrease in the residual service life of the units and the reliability of the machines in general. Under unsteady load conditions, friction in the joints of hydraulic drive elements occurs under the boundary lubrication regime. This lubrication mode occurs at high contact loads, high temperatures in the contact zone, and relatively low sliding speeds of the mating surfaces. The combination of boundary lubrication and high dynamic loads often leads to partial destruction of the boundary layer. This leads to direct contact of individual micro-irregularities of the friction surfaces, which is accompanied by a wear process. Hence the importance of the quality of both the parameters of the surface layer of friction surfaces and the parameters of the applied lubricant (oils, working fluids) on the strength and wear resistance of hydraulic drive elements. Goal. The aim of this work is to determine the effect of temperature and radius of curvature of a microroughness on the thickness of the layer of surface-active substances adsorbed on it. Methodology. The solution of the tasks involved the formation of a model of adsorption-desorption equilibrium in the system "working fluid - micron-surface", taking into account the ambient temperature, and its application to determine the dependence of the thickness of the adsorbed surfactant layer under conditions of temperature change. Results. The thickness of the adsorption layer depends mainly on the size of the adsorbing surface field and the energy of thermal vibrations of molecules. It decreases with increasing PP and increases with increasing radius of curvature of the micron roughness. The change in the thickness of the adsorption layer of surfactant molecules on the surface of the micron roughness with a change in the temperature of the RS is not uniform. With an increase in the PP temperature within 300...400 K, the thickness of the adsorption layer of surfactant molecules on the surface of the micron roughness decreases by ~24 %. With an increase in the temperature of the PP in the range of 400...450 K, the thickness of the adsorption layer of surfactant molecules on the surface of the microroughness decreases by ~76 %. The formation of a surfactant adsorption layer on the surface of the microroughness at a temperature above 443 K stops. Originality. A model of the formation of a surfactant adsorption layer on the surface of a separate microroughness on the basis of adsorption-desorption equilibrium in the system "working fluid - microroughness surface" was proposed, taking into account the ambient temperature, which allows us to analyse the nature of the temperature effect on the thickness of the adsorbed surfactant layer. Practical value. The use of the proposed mathematical model makes it possible to estimate the parameter of the surfactant adsorption layer on the surfaces of microroughnesses and rough friction surfaces based on the ambient temperature and the geometry of individual microroughnesses.

O/D emulsions stabilized by quaternary ammonium gemini surfactants together with alumina nanoparticles

AbstractOil‐in‐dispersion (O/D) emulsions are the focus in many fields due to their new microstructures and new functions. Herein, O/D emulsions were successfully prepared using series of cationic gemini surfactants 12‐s‐12 (s = 2, 3, and 6) and alumina nanoparticles. The microstructures and type of emulsions were identified using optical microscopy, zeta potential and contact angle methods. Gemini surfactants with two head groups carry more charges than that of conventional surfactants when adsorbed at the oil–water interface. The O/D emulsions can be stabilized at lower surfactant concentrations compared with the conventional single‐headed surfactants. In the presence of 0.1 wt% alumina nanoparticles, gemini surfactants 12‐s‐12 (s = 2, 3, and 6) can stabilize emulsions at the concentration of 3 × 10−4 mM (1.84 × 10−5 wt%), 6 × 10−4 mM (3.76 × 10−5 wt%) and 1 × 10−3 mM (6.68 × 10−5 wt%), respectively. Addition of excessive organic salts such as sodium salicylate and sodium p‐methylbenzenesulfonate shielded the head group charges of gemini surfactants, leading to gemini surfactants to behave as nonionic surfactants Adsorption of surfactants at the alumina nanoparticles occurred, resulting in the transformation from the O/D emulsions to Pickering emulsions. This work shows the advantages of preparing O/D emulsions using gemini surfactants and also provides a new methods of emulsion type transformations by adding excessive oppositely charged organic salts.

Highly efficient recovery of viscous oil through nondispersive solvent extraction using polydopamine modified PVDF Janus membrane

Viscous oil separation and its highly efficient recovery is a great challenge in oil/water separation applications. Membrane separation was considered as a prospective strategy for oil/water separation, but membrane contamination caused by the oil droplets restricted its applications significantly. We here propose a nondispersive solvent extraction strategy to efficiently recover viscous lubricant oil from emulsions via a polydopamine modified PVDF Janus membrane. The incorporated thin polydopamine layer facilitates the adsorption and diffusion of surfactant stabilized oil droplets through the membrane. We studied the influence of polydopamine coating time, the flow rate on both feed and extraction sides, the weight content of lubricant oil on the recovery of oil. The optimized membrane exhibited a 10 h accumulative flux (1595 g·m−2) for viscous lubricant oil in water emulsion, which was 70 % higher than the contrast PVDF membrane. The current study might significantly advance application of this novel method for highly efficient separation and recovery of viscous oils from oil/water mixtures.