Low Surfactant Research Articles

Identification of key surfactant in municipal solid waste leachate foaming and its influence mechanism

Serious foaming problems and the excessive consumption of defoamer have undoubtedly become one of the most critical problems that hinder municipal solid waste (MSW) leachate treatment efficiency and industry development. Since there is limited research penetrating the foaming mechanism and identification of the key surfactants, current defoaming and surfactant removal techniques lack pertinence and orientation. In this study, a foaming characterization device was developed and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC/MS/MS) was optimized to accurately identify the key surfactants affecting leachate foaming and offer a glimpse into their interaction mechanisms. This study collected leachate samples from 9 typical landfills and waste-to-energy facilities of various waste compositions, climatic conditions, ages, and geographical locations. The foaming problem of leachate was mainly centered on raw leachate and nanofiltration membrane concentrate (NFC). Fresh leachate performed with relatively low foaming capacity and foam stability, associated with low surfactant concentration. The pH value of the system was positively correlated with the concentration of anionic surfactants, indicating significant impacts on surfactant release in MSW. Since the distribution characteristics of linear alkylbenzene sulfonate (LAS) in leachate were consistent with the variety of foaming performances, LAS proved to be an indispensable surfactant in the leachate involved in this study, and its content proportion escalated to 92.87% in aged leachate.

A new method for measuring the dynamic interfacial tension for flowing droplets of three-phase emulsion in the channel

• We invent a method to measure dynamic interfacial tension of three-phase emulsion. • The real-time acquisition of dynamic interfacial tension in the channel is obtained. • The γ-t relationship shows the surfactant adsorption exist throughout the channel. • Ca - t images of various surfactant concentrations show different transfer mechanisms. In this work, we developed a method for measuring the dynamic interfacial tension of three-phase emulsion based on microfluidic devices. The interfacial tension of three-phase emulsion in the flow process changes rapidly and is difficult to measure, which has never been reported in the previous literature. Through the geometric analysis of the structure of three-phase emulsion, the MATLAB program is compiled to simulate the image. By combining the simulated images with the high-speed photographic images of the flowing droplet, the dynamic interfacial tension during the structural transformation of emulsion is derived. This method can obtain the interfacial tension of flowing droplets in microchannels in real time, especially for three-phase emulsion, and can calculate the instantaneous interfacial tension at an interval of 4 ms. The error range of the measured dynamic interfacial tension value is not more than 0.1 mN / m , which is relatively accurate. We also use the measured dynamic interfacial tension to draw the Ca - t image, which shows the obvious differences at high and low surfactant concentrations. This is due to the different mass transfer resistance of surfactants at high and low concentrations. In a short, this study helps us to further understand how surfactants diffuse during the flow process of three-phase emulsions, which further helps us to better regulate the emulsions.

Micellar enhanced ultrafiltration of phenol with dodecylpyridinium chloride and sodium dodecylbenzene sulfonate

AbstractMicellar enhanced ultrafiltration is a surfactant‐based separation process for wastewater treatment. The ultrafiltration of dodecyl pyridinium chloride (DPC) and sodium dodecyl benzene sulfonate (SDBS) solutions was realized with 5 kDa and 15 kDa molecular weight cut‐off ceramic membranes. Surfactant concentrations under and over the micellar critical concentration at three different pressures were studied, and their effects on permeate flux and retention are reported. It was found that an increase in pressure operation, in 0.8–1.8 bar range, causes a lower surfactant concentration in permeate by the presence of a polarization layer. These systems were studied for phenol removal. DPC/phenol system (73.5 mM/0.53 mM) reaches a 61% removal of organic solute. SDBS/phenol system (14.7 mM/0.58 mM) reaches a 25% removal, both with 5 kDa membrane at 1.8 bar. In the case of the cationic surfactant the micelle's positive charge plays a preponderant role in attracting the phenol molecules, while the SDBS does not present this electrostatic interaction.

Microemulsion Delivery Systems with Low Surfactant Concentrations: Optimization of Structure and Properties by Glycol Cosurfactants.

Extensive use of microemulsions as delivery systems raises interest in the safe ingredients that can form such systems. Here, we assessed the use of two glycols, i.e., propylene glycol and pentylene glycol, and their mixtures to manipulate the properties and structure of microemulsions. Obtained systems with glycols were extensively characterized in terms of capacity to incorporate water phase, droplet size, polydispersity, structure type, and rheological and thermal properties. The results of these studies indicate that the composition, structure, and viscosity of the microemulsions can be changed by appropriate quantification of glycols. It has been shown that the type of glycol used and its amount may favor or worsen the formation of microemulsions with the selected oils. In addition, a properly selected composition of oils and glycols resulted in the formation of microemulsions with a reduced content of surfactants and consequently improved the safety of using microemulsions as delivery systems.

Modelling of removal of surfactants from liquid solutions in a bubble column

This paper proposes a theoretical model for the separation of a surfactant from water in a bubble column. The proposed model includes both mass balance and adsorption thermodynamics of surfactants on bubble surfaces in the liquid solution (e.i. surface equations of state and adsorption isotherms). This is very important because models, found in the literature, did not consider adsorption thermodynamics. The proposed model successfully predicted the experimental results. It was found that the separation efficacy was higher at a lower surfactant concentration in the liquid than that at a higher surfactant concentration; the reason is probably that available bubble surface areas for adsorption of the surfactant were higher at a lower surfactant concentration. A higher cross-sectional area of the column led to a better separation performance due to a larger amount of generated bubble surfaces. A low gas flow rate and low liquid fraction resulted in the best separation performance.

Diffusiophoresis of a Nonionic Micelle in Salt Gradients; Roles of Preferential Hydration and Salt-Induced Surfactant Aggregation.

Diffusiophoresis is the migration of a colloidal particle in water driven by concentration gradients of cosolutes such as salts. We have experimentally characterized the diffusiophoresis of tyloxapol micelles in the presence of MgSO4, a strong salting-out agent. Specifically, we determined the multicomponent-diffusion coefficients using Rayleigh interferometry, cloud points, and dynamic-light-scattering diffusion coefficients on the ternary tyloxapol-MgSO4-water system at 25 °C. Our experimental results show that micelle diffusiophoresis occurs from a high to a low salt concentration (positive diffusiophoresis). Moreover, our data were used to characterize the effect of salt concentration on micelle size and salt osmotic diffusion, which occurs from a high to a low surfactant concentration. Although micelle diffusiophoresis can be attributed to the preferential hydration of the polyethylene glycol surface groups, salting-out salts also promote an increase in the size of micellar aggregates, ultimately leading to phase separation at high salt concentration. This complicates diffusiophoresis description, as it is not clear how salt-induced surfactant aggregation contributes to micelle diffusiophoresis. We, therefore, developed a two-state aggregation model that successfully describes the observed effect of salt concentration on the size of tyloxapol micelles, in the case of MgSO4 and the previously reported case of Na2SO4. Our model was then used to theoretically evaluate the contribution of salt-induced aggregation to diffusiophoresis. Our analysis indicates that salt-induced aggregation promotes micelle diffusiophoresis from a low to a high salt concentration (negative diffusiophoresis). However, we also determined that this mechanism marginally contributes to overall diffusiophoresis, implying that preferential hydration is the main mechanism causing micelle diffusiophoresis. Our results suggest that sulfate salts may be exploited to induce the diffusiophoresis of PEG-functionalized particles such as micelles, with potential applications to microfluidics, enhanced oil recovery, and controlled-release technologies.

Thermodynamics of Aggregation between the Cationic Surfactant and Polymer Based on Biodegradable Poly(vinyl Alcohol).

The formation of aggregates between carboxylated (PVCOOH) or neutral hydrolyzed (PVOH) poly(vinyl alcohol) and hexadecylpyridinium chloride (C16PyCl) was examined by conductimetry, turbidimetry, and isothermal titration calorimetry (ITC) in the presence of different NaCl concentrations. The interaction between the polymers and C16PyCl in pure water showed a critical aggregation concentration (cac = 0.8 mmol L-1) only for the neutral polymer. PVCOOH interacted with the surfactant through electrostatic attraction, forming macroscopic aggregates. Integral enthalpy changes for aggregate formation (ΔHagg) obtained from ITC curves varied from -0.61 (for the PVOH system in pure water) to -4.14 kJ mol-1 (for PVOH in the presence of 10.0 mmol L-1 NaCl), indicating that the formation of the aggregates was enthalpically favored. However, hydrophobic interactions drove the process for low surfactant concentration for both polymers. Saturation concentrations (C2) obtained from conductimetry were smaller than those from ITC, revealing that the binding of C16PyCl on the chain of the polymers at higher surfactant concentrations shows the same electric properties as that of free micelles on the solution. Increase of the ionic strength favored the aggregation and decreased the complexity of the ITC curves, suggesting that the reorganization of the surfactant monomers on the polymeric chain with the increase in their concentration was suppressed.

Exploring drug-surfactant interactions and their impact on the intrinsic surface properties of aqueous dissolution media

Surfactants are often used to improve the solubility of a compound for dissolution studies in aqueous media. Having observed non-linear solubility enhancement with increasing surfactant concentration, this study investigated the effect of a poorly soluble, zwitterionic, moderately lipophilic drug, Compound A, on the critical micelle concentration (CMC)of sodium lauryl sulfate (SLS) in phosphate buffer. A force tensiometer was used to measure the surface tension of the solutions over a range of surfactant concentrations. The presence of Compound A demonstrated a decrease in the CMC, suggesting that the solution favours micellisation at lower surfactant concentrations in the presence of the drug. Future studies will use a fully saturated solution of Compound A to explore this observation further. Additional experiments will also investigate micelle formation of SLS with other compounds.

Experimental Study on Alternating Injection of Silica and Zirconia Nanoparticles with Low Salinity Water and Surfactant into Fractured Carbonate Reservoirs for Enhanced Oil Recovery

Recently, the application of low salinity water (LSW), nanoparticles (NPs), and surfactants (collectively abbreviated as LNS) in carbonate formations for enhanced oil recovery (EOR) purposes has been under investigation, but relatively few studies have been performed for their implementation in fractured carbonate reservoirs (FCRs). The objective of this study is to apply the recently proposed method of alternatively injecting LNS in cycles into FCRs using silica and zirconia NPs. The cumulative oil recovered from the two coreflooding experiments performed at 3000 psi overburden pressure and 70 °C temperature is reported in this study in addition to spontaneous imbibition (SI) experiments. The experimental design is structured to depict the best industrial practice for the injected fluids in FCRs. Furthermore, this work investigates the effect of zirconia NPs on the interfacial tension (IFT) between the injected fluids and crude oil under the previously stated experimental conditions. The outcome of these experiments divulges that the alternating injection of LNS employing silica and zirconia NPs is effective and well suited for EOR applications in FCRs owing to a cumulative oil recovery of approximately 8 and 7% of the original oil in place (OOIP), respectively. This study validates the implementation of the recently proposed alternating injection of the LNS technique for FCRs and shows its performance utilizing newly acquired zirconia NPs, which is relevant for industrial application at a large scale.

Probing Molecular Interactions of Antibody Drugs, Silicone Oil, and Surfactant at Buried Interfaces In Situ.

Antibody drugs have been rapidly developed to cure many diseases including COVID-19 infection. Silicone oil is commonly used as a lubricant coating material for devices used in the pharmaceutical industry to store and administer antibody drug formulations. However, the interaction between silicone oil and antibody molecules could lead to the adsorption, denaturation, and aggregation of antibody molecules, impacting the efficacy of antibody drugs. Here, we studied the molecular interactions between antibodies and silicone oil in situ in real time. The effect of the surfactant on such interactions was also investigated. Specifically, the adsorption dynamics of a bispecific antibody (BsAb) onto a silicone oil surface without and with different concentrations of the surfactant PS80 in antibody solutions were monitored. Also the possible lowest effective PS80 concentrations that can prevent the adsorption of BsAb as well as a monoclonal antibody (mAb) onto silicone oil were measured. It was found that different concentrations of PS80 are required for preventing the adsorption of different antibodies. Both BsAB and mAB denature on silicone oil without a surfactant. However, for a low surfactant concentration in the solution, although the surfactant could not completely prevent the antibody from adsorption, it could maintain the native structures of adsorbed BsAb and mAb antibodies on silicone oil. This is important knowledge, showing that to prevent antibody aggregation on silicone oil it is not necessary to add surfactant to a concentration high enough to completely minimize protein adsorption.

Insight into binding mechanism between three whey proteins and mogroside V by multi-spectroscopic and silico methods: Impacts on structure and foaming properties

In this work, the interaction mechanism, structure and foaming properties between three whey proteins (α-lactalbumin (ALa), β-lactoglobulin (BLg) and bovine serum albumin (BSA)) and Mogroside V (Mog) at pH 7.0 were systematically formulated via multi-spectroscopic analysis and silico methods. Mog quenched the fluorescence of three whey proteins in a static mode. Mog had greater binding affinity for ALa than that for BLg or BSA. Hydrogen bonds, van der Waals force and hydrophobic interaction acted as the primary driven forces in ALa/BLg/BSA-Mog system. Moreover, content of α-helix in ALa and β-sheet in BLg decreased after Mog addition, whereas there was no significant change in the secondary structure of BSA. In addition, hydrophobic crevice in ALa, “bottom of β-barrel” in BLg and interfacial region between two domains in BSA were the binding areas for Mog using molecular docking. Molecular dynamics (MD) simulation further demonstrated that the complex of ALa and Mog possessed the lowest binding free energy and most stable state. Furthermore, compared with single proteins, the foaming ability of protein/Mog complexes were improved. Especially, Ala-Mog attained the highest increase rate. Bubble morphology presented that three whey proteins containing Mog possessed compacter, smaller and even bubbles. This research could establish theoretical basis for the binding mechanism between different food proteins and low weight surfactants. Besides, whey protein-saponin complexes could be served as the novel food-grade foaming agents applied in food industry.

Intrinsic lipolysis rate for systematic design of lipid-based formulations

Lipid-based formulations (LBFs) are used by the pharmaceutical industry in oral delivery systems for both poorly water-soluble drugs and biologics. Digestibility is key for the performance of LBFs and in vitro lipolysis is commonly used to compare the digestibility of LBFs. Results from in vitro lipolysis experiments depend highly on the experimental conditions and formulation characteristics, such as droplet size (which defines the surface area available for digestion) and interfacial structure. This study introduced the intrinsic lipolysis rate (ILR) as a surface area-independent approach to compare lipid digestibility. Pure acylglycerol nanoemulsions, stabilized with polysorbate 80 at low concentration, were formulated and digested according to a standardized pH–stat lipolysis protocol. A methodology originally developed to calculate the intrinsic dissolution rate of poorly water-soluble drugs was adapted for the rapid calculation of ILR from lipolysis data. The impact of surfactant concentration on the apparent lipolysis rate and lipid structure on ILR was systematically investigated. The surfactant polysorbate 80 inhibited lipolysis of tricaprylin nanoemulsions in a concentration-dependent manner. Coarse-grained molecular dynamics simulations supported these experimental observations. In the absence of bile and phospholipids, tricaprylin was shielded from lipase at 0.25% polysorbate 80. In contrast, the inclusion of bile salt and phospholipid increased the surfactant-free area and improved the colloidal presentation of the lipids to the enzyme, especially at 0.125% polysorbate 80. At a constant and low surfactant content, acylglycerol digestibility increased with decreasing acyl chain length, decreased esterification, and increasing unsaturation. The calculated ILR of pure acylglycerols was successfully used to accurately predict the IRL of binary lipid mixtures. The ILR measurements hold great promise as an efficient method supporting pharmaceutical formulation scientists in the design of LBFs with specific digestion profiles.Graphical abstract

The suspending appearance of poly(acrylic acid)‐based rheology modifier in high‐content surfactant: The effect of polymer structure and molecular weight on the rheological properties of the complex systems

AbstractThe “all in one” multifunctional and concentrated daily chemical products are required by the market, such as the long‐term release of anti‐bacterial, medical, or perfume agents. These functions mainly rely on the microcapsules, which could encapsulate these functional and unstable molecules, and then release them in the long term. To stabilize these functional solid particles in a high‐content surfactant, it is necessary to add a suspending rheological modifier. The poly(acrylic acid) (PAA)‐based rheology modifier is one of the most common additives in the industry of daily chemicals, for thickening or suspending. In this paper, linear PAA, and branched PAA polymers (Carbomer 941 and Carbomer 940) were selected to study the suspending ability of PAA‐based rheology modifier in high‐content surfactant and to investigate the effect of PAA polymer structure and Mw on the complex solution's rheological properties. The yield and viscosity test of the complex solutions of linear PAA and high‐content surfactant revealed that the addition of linear PAA could lead to lower yield stress and viscosity, and failed to suspend the polystyrene (PS) model microspheres due to its smaller mean square radius of gyration. The branched PAA polymer, Carbomer 940 and Carbomer 941 were more stable than the linear PAA in these two kinds of surfactant. More specifically, Carbomer 940 with a higher Mw, would exhibit higher yield stress and viscosity than Carbomer 941 with a lower Mw in nonionic surfactant alcohol polyoxyethylene ether (AEO) solvent with content less than 5 wt%. When the content was higher than 5 wt%, Carbomer 941 presented higher yield stress and viscosity than Carbomer 940, and successfully suspended PS microspheres in the 20 wt% AEO solution. This could depend on the polymer chain's elongation state of these two PAA‐based branched rheology modifiers. The same trend happened in the appearance of Carbomer 940 and Carbomer 941 in alcohol ether sulphate (AES) solution. However, the electrostatic repulsive force between the AES and PAA‐based rheology modifier could further make the polymer chain curl up and restrain the suspending ability in a lower content surfactant solution. Therefore, this fundamental research could guide the application of the anionic polyelectrolytes in the concentrated daily chemical product for stable suspending particles.

Horseradish peroxidase-catalyzed synthesis of high-quality polyaniline in Good’s buffer ionic liquid-buffered H2O/AOT/isooctane bicontinuous microemulsion

Here, a functionalized organic salt composed of [Nk,k,k,k]+ (k = 1–4) and [MES]- (2-(N-morpholino)ethanesulfonate), i.e., Good’s buffer ionic liquid with self-buffering and biocompatible properties, was chosen as electrolyte as well as buffer to construct a H2O/AOT/isooctane bicontinuous microemulsion for enzymatic synthesis of polyaniline (PANI). Studies on the effects of the functionalized organic salt on the phase behavior indicate that [Nk,k,k,k][MES] can tune the phase inversion temperature of AOT-stabilized oil-water microemulsion system through changing the cationic alkyl chain length, exhibiting the properties of both inorganic salt and co-alcohol. More interestingly, the stability of horseradish peroxidase (HRP) solubilized in the H2O(0.1 M [N1,1,1,1][MES], pH = 4.5)/AOT/isooctane bicontinuous microemulsion is much better than that formulated with mixed surfactants AOT/SB-12 and inorganic salt. Studies on the HRP-catalyzed oxidative polymerization of aniline in the present bicontinuous microemulsion indicates that at low surfactant content and high oil-water ratio, the present microemulsion resulted in a PANI with better conductivity than the counterpart reported elsewhere. This work is of guiding significance for constructing a less-component and enzyme-compatible bicontinuous microemulsion for template-assisted biopolymerization.

Mannose-based surfactant as biofunctional nanoemulsion stabilizer

The development and implementation of new amphiphiles based on natural resources rather than petrochemical precursors is an essential requirement due to their feedstock depletion and adverse environmental impacts. In addition, the use of bio-based surfactants can provide unique characteristics and improve the properties and versatility of the colloidal systems in which they are applied, such as emulsions. Here, the emulsification properties of a synthesized biocompatible mannose-based surfactant were investigated. Its behavior was evaluated in the presence of four different natural oils (castor, sunflower, olive and soybean) as well as two different aqueous phases (pure water and phosphate-buffered saline). The results highlighted its interest as surfactant in O/W nanoemulsions for all tested oil and aqueous phases, using a low-energy preparation protocol and relatively low surfactant concentrations. Furthermore, the mannose groups present on the polar head of the surfactant and adsorbed on the surface of the emulsion droplets were shown to retain their native biological properties. The specific mannose-concanavalin A binding was observed in vitro by the designed nanoemulsions, revealing the biorecognition properties of the surfactant and its potential applicability as a nanocarrier.

Solid lipid nanoparticles and nanostructured lipid carriers of dual functionality at emulsion interfaces. Part I: Pickering stabilisation functionality

Solid lipid nanoparticles and nanostructured lipid carriers are two types of lipid nanoparticulate systems, that have been primarily studied for their capability to function as active carriers, and only more recently utilised in Pickering emulsion stabilisation. Unveiling the factors that impact upon the lipid particle characteristics related to their Pickering functionality could enable the development of a liquid formulation with tailored microstructure and potentially the capacity to display a two-fold performance. In part I, this work investigates how certain formulation characteristics, namely solid-to-liquid lipid mass ratio and presence of unadsorbed surfactant in the aqueous carrier phase, affect the structural properties of the lipid particles, and in turn how these influence their Pickering stabilisation capacity. The effect of the formulation parameters was assessed in terms of the wettability and physicochemical properties of the lipid particles, including particle size, crystallinity and interfacial behaviour. Lipid particles fabricated with higher liquid lipid content (70% w/w) were shown to be more hydrophilic and have lower surfactant decoration at their surface compared to particles containing lower or no liquid lipid in their crystalline matrix. The emulsion stabilisation ability through a Pickering mechanism was confirmed for all types of lipid particles using polarised microscopy. Increasing liquid lipid content and removal of excess surfactant did not compromise the particle stabilisation capacity, though emulsion droplets of larger sizes were initially acquired in the latter case. The particle-stabilised emulsions maintained their physical integrity, with particles retaining close association with the emulsion interface over a storage period of 12 weeks.

Comparison of the Performance of Different Bile Salts in Enantioselective Separation of Palonosetron Stereoisomers by Micellar Electrokinetic Chromatography.

Bile salts are a category of natural chiral surfactants which have ever been used as the surfactant and chiral selector for the separation of many chiral compounds by micellar electrokinetic chromatography (MEKC). In our previous works, the application of sodium cholate (SC) in the separation of four stereoisomers of palonosetron (PALO) by MEKC has been studied systematically. In this work, the parameters of other bile salts, including sodium taurocholate (STC), sodium deoxycholate (SDC), and sodium taurodeoxycholate (STDC) in the separation of PALO stereoisomers by MEKC were measured and compared with SC. It was found that all of four bile salts provide chiral recognition for both pairs of enantiomers, as well as achiral selectivity for diastereomers of different degrees. The structure of steroidal ring of bile salts has a greater impact on the separation than the structure of the side chain. The varying separation results by different bile salts were elucidated based on the measured parameters. A model to describe the contributions of the mobility difference of solutes in the aqueous phase and the selectivity of micelles to the chiral and achiral separation of stereoisomers was introduced. Additionally, a new approach to measure the mobility of micelles without enough solubility for hydrophobic markers was proposed, which is necessary for the calculation of separation parameters in MEKC. Under the guidance of derived equations, the separation by SDC and STDC was significantly improved by using lower surfactant concentrations. The complete separation of four stereoisomers was achieved in less than 3.5 min by using 4.0 mM of SDC. In addition, 30.0 mM of STC also provided the complete resolution of four stereoisomers due to the balance of different separation mechanisms. Its applicability for the analysis of a small amount of enantiomeric impurities in the presence of a high concentration of the effective ingredient was validated by a real sample.

Renewable non-edible oils derived long chain (C24.1) bio-based zwitterionic surfactant with ultralow interfacial tension between crude oil and formation brine

A new ultra-long chain monounsaturated 4-(N-nervonicamidopropyl-N,N-dimethylammonium) butane sulfonate (NDAS) zwitterionic surfactant with ultralow interfacial tensions was developed through the modification of nervonic acid derived from renewable non-edible seed oils by a simple and effective method. Its structure was characterized by ESI-HRMS, 1H NMR, and 13C NMR. NDAS surfactant exhibited a strong interfacial activity (∼10−4 mN/m) between the crude oil and the formation brine at a very low surfactant dosage (0.05 g/L) and at high salinity conditions, which is equivalent to 2% (w/w) of dosage of the most traditional surfactants used in the enhanced oil recovery field. Meanwhile, at a very low concentration (0.05 g/L), NDAS demonstrated strong NaCl compatibility up to 100 g/L, Ca2+ ions compatibility up to 200 mg/L, and temperature stability up to 90 °C. The surface tension, emulsification, and biodegradability parameters were also evaluated. This work consolidates our hypothesis that increasing the hydrophobic chain length of a surfactant certainly contributes to the high interfacial activity and good compatibility of salts and temperatures. Hence, it will facilitate the design of a sustainable alternative to petroleum-based chemicals to develop bio-based surfactants and extend the domain of bio-based surfactants to new applications such as in enhanced oil recovery (EOR).

Impact of salinity on fluid/fluid and rock/fluid interactions in enhanced oil recovery by hybrid low salinity water and surfactant flooding from fractured porous media

Wettability alteration of the porous medium from oil-wet (OW) to neutral-wet or even water-wet (WW) is proposed as one of the main mechanisms behind the enhanced oil recovery (EOR) by the Low Salinity Water Flooding (LSWF). However, our recent studies for a specific crude-oil/brine/rock of the oil reservoir in the Middle East, shows that LSW (diluted sea water) is not that much effective, neither to change the wettability of the surface nor to significantly increase the oil recovery factor. This obstacle becomes more challenging when we deal with fractured formations, where the imbibition of injected fluid from fracture into matrix and its propagation within the matrix, is the main macroscopic mechanism of the EOR. Chemical EOR, in which the chemical additive is added to the injecting brine, is one of the hybrid techniques which can boost oil recovery in such cases. In this study, CTAB as a cationic surfactant was added to brine solutions with different ionic strengths (i.e., sea water (SW), 10 times diluted sea water (10dSW) and 2 times concentrated sea water (2cSW)). Contact angle, zeta potential of both fluid/fluid and fluid/rock surfaces, and IFT tests were conducted to shed insight on interactions in crude oil/brine and rock/brine interfaces and the role of ionic strength. Finally, dynamic micromodel tests were performed in oil-wet fractured porous media to observe the impact of the added surfactant along with different ionic strength on displacement mechanisms and oil recovery.Experimental results show that neither electrical double layer expansion nor multiple ion exchange mechanisms cannot justify the observed detachment of oil droplets from the oil-wet substrates in the presence of the CTAB. Surfactant are absorbed on the oil/brine interface by the embedment of their hydrophobic tails in oil. Both surfactant molecules and the non-polar oil components (that are attracted to hydrophobic tail of surfactant molecules), are attracted to the solution via the hydrophilic parts of the surfactants. The effectiveness of this mechanism is dependent on both the concentration of the surfactant and concentration of the ions in brine.In the case that the aforementioned mechanism is adequately dominant and effective, the small droplets of oil will be detached from continuous oil bulk, resulting in oil to be broken to smaller droplets which enhances the detachment of the oil bulk from oil-wet substrates. This fluid/fluid interaction mechanism also promotes the imbibition of the aqueous phase into the matrix and also its propagation within the matrix.

Surfactant-Assisted Assembly of Dipeptide Forming a Broom-like Structure.

Understanding the influence of surfactants on the assembly of peptides has a considerable practical motivation. In this paper, we systematically study the anionic surfactant-assisted assembly of diphenylalanine (FF). FF forms broom-like structures in a concentration of sodium cholate (NaC) around the CMC, and assembles into linear and unidirectional rods in the presence of low and high surfactant concentrations. FF’s improved hydrogen bonding and controlled assembly rates are appropriate for other anionic surfactants. At this stage, the use of FF as the simplest protein consequence can be helpful in the investigation of further protein–surfactant interactions.